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Electrical Structure from O to 30 Kilometers 1 (a) INTRODUCTION WOLFGANG GRINGEL Universitat Tubingen JAMES M. ROSEN and DAVID ]. HOFMANN University of Wyoming This chapter deals with the electrical structure of the lower atmosphere, i.e., the troposphere and the portion of the stratosphere below about 30 km. Here the princi- pal observing platforms (not including surface measure- ments) are balloons. Their limited height range, rather than other physical considerations, is the main reason that the electrical structure above 30 km will be dis- cussed separately in the following chapter. For better understanding of the electrical phenomena taking place in the lower atmosphere and the coupling between them, the concept of a "global circuit" will be briefly touched on a complete discussion is presented by Roble and Tzur (Chapter 15, this volume). The discovery of the atmospheric conductivity raised a question concerning the origin of the electric fields and the electric currents that were known to exist and flow continuously in the atmosphere. According to the classi- cal picture of the global circuit (Dolezalek, 1972), the total effect of all thunderstorms acting at the same time can be regarded as the global generator, which charges the ionosphere to several hundred kilovolts with respect to the Earth's surface. This potential difference drives the air-earth current downward from the ionosphere to the ground in the nonthunderstorm areas through the concluctive atmosphere. The value of this air-earth cur 166 rent density varies according to the ionospheric poten- tial and the total columnar resistance between iono- sphere and ground. Finally the local atmospheric electric field must be consistent with this current flow- ing through a resistive medium, i.e., the atmosphere. In addition to the global generator there also exist ef- fective local generators such as precipitation, convec- tion currents (charges moved by other than electrical forces), and blowing snow or dust. The latter create their own local current circuits and electric fields super- imposed on parts of the global circuit. Generators can be regarded as local generators (Dolezalek, 1972) if the re- sistance from the upper terminal to the ionosphere is much greater than the resistance from that point to the Earth's surface along the shortest possible path and with the consequence that almost no current flows to the ion- osphere from this generator. In the following sections we discuss initially the sources of ionization in the lower atmosphere together with solar-induced and latitudinal variations. In the next section a brief review of aerosol distributions in the troposphere and lower stratosphere is presented. Varia- tions following major volcanic eruptions are empha- sized. Atmospheric conductivity, small ion concentra- tions, and ion-mobility measurements are the subject of the third section. Here the influence that solar activity or aerosols have on the conductivity, and therefore on

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS parts of the columnar resistance, are discussed. In the final section the air-earth current and electric fields in the lower atmosphere are considered. lIere the results are interpreted from a global viewpoint with perturba- tions from local generators. Examples of anthropogenic influences on the electric field near the ground are also presented and discussed briefly. ION PRODUCTION IN THE LOWER ATMOSPHERE The electric structure of the troposphere and lower stratosphere depends strongly on the ion-pair produc- tion rate and the physical properties of the ions pro- duced. Cosmic rays are the primary source of ionization in the atmosphere range under consideration. Near the Earth's surface over the continents there is an additional component due to ionization by radioactive materials exhaling from the soil. This radioactive ionization com- ponent depends on different meteorological parameters and can exceed the cosmic-ray component by an order of magnitude as discussed in Chapter 11. It decreases rapidly with increasing height, and at 1 km it is already significantly less than the contribution due to cosmic rays (Pierce and Whitson, 1964~. The ion-production rate by cosmic rays is shown in Figure 12.1 for different geomagnetic latitudes during the years of solar mini h/km ~0 _ ~ 20 ~ 10 _ Neher (1961,1967) 73\ 1965 73O> - - - 1958 35~ ~~ _ __ > q/ -3 -1 O _ 0 10 20 30 40 50 FIGURE 12.1 Profiles of the ionization rate at different latitudes in years of the minimum (1965) and maximum (1958) of the 11-yr solar sunspot cycle (Neher, 1961, 1967~. 167 mum (1965) and solar maximum (1958) based on bal- loon measurements by Neher (1961, 1967~. The exis- tence of the geomagnetic field gives rise to a pronounced latitude effect. Only at latitudes higher than about 60 can the full energy spectrum of the cosmic rays reach the Earth and the depth of penetration be limited only by the increasing atmospheric density for low-energy parti- cles. At high latitudes 100-MeV protons can penetrate to about 30 km height, for example. Moving downward to lower latitudes more and more particles with lower en- ergies are deflected by the geomagnetic field and, there- fore, are excluded. The geomagnetic equator itself can only be reached by particles with energies greater than about 15 GeV. The hardening of the cosmic-ray spec- trum with decreasing latitude is indicated in Figure 12.1 by the lowering of the height at which the maximum ionization rate occurs. Near the equator this maximum ionization rate is observed around 10 km. Furthermore, the ionization rate depends strongly on solar activity in a sense that at a particular height the ion-production rate is lower during the sunspot maxi- mum and higher during the sunspot minimum, as illus- trated in Figure 12.1. The mechanisms are not fully understood, but it appears that irregularities and enhancements of the interplanetary magnetic field tend to exclude part of the lower-energy cosmic rays from the inner solar system (Barouch and Burlaga, 1975~. The effect becomes more pronounced with increasing height and/or increasing geomagnetic latitude. At geomag- netic latitudes around 50 the reduction of the ion-pro- duction rate during the periods of sunspot maximum is about 30 percent at 20 km and about 50 percent at 30 km. More recently this solar-cycle dependence was con- firmed by measurements with open balloonborne ion- ization chambers by Hofmann and Rosen (1979~. Ana- lytical expressions for computing the ionization rates dependent on latitude and solar-cycle period are given by Heaps (1978~. Superimposed on the 11-yr solar-cycle variation are so-called Forbush decreases (Forbush, 1954), which are somehow related to solar flares and exhibit a temporary reduction of the incoming cosmic- ray flux for periods of a few hours to a few days or weeks (Duggal and Pomerantz, 1977~. On the other hand, solar proton events (SPE) can drastically increase the ion-production rate within the stratosphere and, for high-energy solar protons, some- times even near the ground. The duration of such SPEs is of the order of hours, and they are normally restricted to high-latitude regions, as discussed in more detail in the following chapters.

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168 AEROSOLS IN THE LOWER ATMOSPHERE Within the portion of the atmosphere under consider- ation in this chapter there are three primary regions of interest to atmospheric electricity: the boundary layer (approximately the first 3 to 5 km), the remaining por- tion of the troposphere, and the stratosphere. The char- acterizing aerosol parameters of central importance here are concentration, size distribution, and vertical structure. In addition, variability of the aerosol in each of these regions must be recognized. Such variations may influence electrical parameters and significantly detract from the apparent repeatability of various at- mospheric electrical measurements. The boundary layer is generally thought of as a rela- tively well-mixed region capped on the upper side by a temperature inversion. Since mixing across the inver- sion tends to be inhibited, a potential exists for the accu- mulation of aerosols within the boundary layer if a sig- nificant source is present. The buildup of aerosols is frequently of sufficient magnitude to cause a notable re- duction in visibility. Even when there is no apparent loss in visibility as observed from the surface, the upper boundary may still be apparent even to an airline pas- senger at the moment when the aircraft passes through inversion. The buildup of aerosols in the boundary layer and the capping effect of the inversion have been ob- served in a more quantitative sense by airborne lidar. The ion concentration and conductivity can be greatly affected by the aerosol buildup in the boundary layer and a dramatic change in these quantities is often ob- served at or near the altitude of the defining inversion. The size distribution of aerosols near the surface of the Earth has frequently been approximated with a power- law function (Junge, 1963~. However, it has more re- cently been suggested that the near-surface aerosol is ac- tually made up of two or three size modes that when added together approximate a power-law function over a limited range of sizes (Willeke and Whitby, 1975~. This interpretation of the size distribution seems to bet- ter reflect the physical processes affecting the aerosol concentration in the atmosphere. Some examples of typ- ical size distributions for a variety of conditions and lo- cations can be found in the work of Willeke and Whitby (1975) and Patterson and Gillette (1977~. The aerosol mixing ratio profile (and usually the con- centration profile) typically show a relative minimum in the upper troposphere for particle radii greater than about 0.1 ,um. In contrast the condensation nuclei (en) profile (corresponding to particle radii of about 0.01 ,um) is more or less constant throughout the entire tro- posphere above the boundary layer. Near the surface of the Earth the en concentration may be relatively high WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN owing to local contamination (104 per cm3 or more), but above the boundary layer the concentration ranges from about 100 to 103 per cm3 with a global average of ap- proximately 300 to 500 per cm3 (Rosen et al., 1978a, 1978b). The size distribution of aerosols in this region of the atmosphere can usually be approximated by a power- law function between about 0.01- and 10-,um particle diameter (Junge, 1963~. Below the minimum size of 0.01,um there are relatively few particles owing to coag- ulation, and above 10 ,um the particle concentration drops quickly from sedimentation effects. Thus limits of the power-law distribution must always be specified. The character of upper tropospheric aerosols can be temporarily disturbed by volcanic eruptions, forest fires, biomass burning, and large dust storms. In addi- tion periodic annual variations of concentration have also been observed (Hofmann et al., 1975~. Another im- portant temporal variation of tropospherical aerosols is associated with the so-called arctic haze events. New ev- idence suggests that these events are characterized by high particle loading throughout a large portion of the troposphere. The impact of this extensive aerosol load- ing on atmospheric electrical parameters is yet to be de- termined. Hogan and Mohnen (1979) reported the results of a global survey of aerosols in the troposphere and lower stratosphere. They found that the concentrations were more or less symmetrically distributed about the Earth. Measurements of this type could provide the basis for extrapolating local or isolated observations to character- istic worldwide values. The morphology of stratospheric aerosols is domi- nated by a persistent structure frequently referred to as the 20-km sulfate layer, or Junge layer. It is now known that the character of this layer is highly affected bY large volcanic eruptions. For several years prior to 1980, stratospheric aerosols were in a quasi-steady-state con- dition, not being under the influence of any significant recent volcanic eruptions. During that period the size distribution appeared to be consistent with a single mode log-normal distribution (Pinnick et al., 1976), al- though other types of single-mode distribution were also employed (Russell et al., 1981) with similar results. The composition was thought to be primarily sulfuric acid droplets. The appearance of the 20-km layer is not evident in the vertical profile of all particle size ranges. The en pro- file, for example, which is representative of particles with sizes in the neighborhood of O. O. l-,um radius usually shows a dramatic drop in concentration above the tro- popause and no relative maximum at the altitude of the stratospheric aerosol layer. This would be consistent

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS with a tropospheric en source and a vertical profile dic- tated by diffusion and coagulation (Rosen et al., 1978a). After a large volcanic eruption the size distribution may be greatly disturbed and highly altitude depen- dent. Following the eruption of E1 Chichon in April 1982, Hofmann and Rosen (1983a, 1983b) reported a size distribution that could be approximated by a sum of multiple log-normal distributions, each with a different mode. The source of the smallest particle mode ~ ~ 0.01 ,um) appeared to be associated with the homogeneous condensation of highly saturated sulfuric acid vapors. This production ceased a few months after the eruption, and consequently the mode disappeared A midsize mode ~ ~ 0.1 Am) was also observed, which may have resulted from coagulation and growth by condensation of the initial particles formed by the homogeneous con- densation. Another mode near 1-2,um diameter was also observed that may have formed from the condensation of sulfuric acid vapors onto the solid silicate ash particles as well as on particles already present in the strato- sphere. Further assessments of the aerosol injected by the E1 Chichon eruption have been described in a collec- tion of papers introduced by Pollack et al. (1983~. An unexpected influence of the E1 Chichon eruption was the enhancement of an annually appearing on layer near 30 km altitude. Although the phenomenon was ob- served in previous years (Rosen and Hofmann, 1983) the concentration of on associated with these event layers was enhanced by at least 2 orders of magnitude. Even though the sizes of the particles were quite small (~O.Ol-,um diameter), the concentration was large enough to measurably affect the ambient ion concentra- tion and conductivity (Gringel et al., 1984~. The event particles are thought to have formed in polar regions from highly supersaturated sulfuric acid vapors. The af- fect of this phenomenon on the various aspects of atmo- spheric electricity at high latitude has not been assessed at the time of this writing. Of particular interest would be the influence of the highly supersaturated vapors on the ambient ion mass (and therefore mobility). Careful measurements at appropriate locations may provide an unexpected means of finding supporting experimental evidence for some of the various models of ion composi- tion (and mass) that have been proposed (Arnold, 1983; Arnold and Buhrke, 1984~. Figures 12.2 to 12.4 illustrate several of the character- istics of atmospheric aerosols that have been discussed above. The long-term influence of volcanic aerosols on the stratosphere are illustrated in Figure 12.2, which compares the quasi-steady-state period with the dis- turbed conditions still observed some 18 months after the eruption of E1 Chichon. Note also the presence of the boundary layer near the surface (as evidenced by a -L I """'I ' """'I " lillIll " """I " IlIlIll 1~ . 20 - _ 50 _ ~_ o: _ ~_ An _ ~, 100 _ in: cat 200 _ 1000 35 27 SEPT 1978 21 OCT. 1983 ~""~_~` ~ (x ~ _,-" ~,_~ /, _ -- ~ __, id, c-~ _ 30 _ 25 ye _ 20 ~ to _ 15 as - 10 , , ,,,,,,1 , , ,,,,,,1 , , 1111111 1 1 ,,,,,,1 , , 1111111 O 103 lo-2 10 1 10 10 1o2 AEROSOL CONCENTRATION ( cm3) DlA. 2 .30,Lm FIGURE 12.2 A comparison of aerosol profiles (particle diameter greater than 0.30 ~m) for the quasi-steady-state period (September 27, 1978) with the decay period following the April 1982 eruption of E1 Chichon. sharp drop in concentration) and a relative minimum in the aerosol concentration occurring in the upper tropo- sphere. An example of a normal and disturbed en profile is illustrated in Figure 12.3. A significant en event layer is evident at about 30 km altitude. Both profiles show a relatively large drop in the on concentration just above the surface, a relatively constant mixing ratio through- out most of the troposphere, and a noticeable drop in concentration near the tropopause. An example of the influence of volcanic eruptions on the size distributions of stratospheric aerosols is illus- trated in Figure 12.4. As previously discussed, the size distribution during the quasi-steady-state period could be described quite well by a single-mode log-normal dis- tribution. At the time of this writing some 18 months after the eruption of E1 Chichon, the size distribution appears still to be quite disturbed.

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170 5 10 . . _ 20 _ 50 _ In `~, 100 a: 200 _ _ 500 _ _ " ""'11 ' """'1 " """1 " """1 " ""I ~ - 15 J AN . 1981 - I FEB. 1983 TROPOPAUSE _ _ - -\~ e;~ ~ %_ ma_ T 35 _ 25 _ 20 ~ lo _ 15~ ,_ _ 5 _ --~ 1000 ~ I I tl''l'1 11''''''1 1 1 l'll1~1 1 1 ''l'll1 1 1 111111 O 10 1 I00101 102 103 104 CONCENTRATION ( cm 3 ) FIGURE 12.3 A comparison of a normal on profile (January 15, 1981) with one obtained during a period of the 30-km on event. tn3 - E . ' ~ At - ~ ~ ~ ~ ~ ~ ~ I I I I 1- 1 1 1 10-1 7 En 10 _ 103 _ 104 _ Ad 105 _ ~ loo _ He at: 10 _ LLI ~ 10 _ 1 SEPT. 1983 NONVOLCANIC PE RIOD \ \ \ \ \\1 '1 .01 .1 R A D I US ( '` m ) FIGURE 12.4 A comparison of the single-mode stratospheric aerosol size distribution (solid line) typical of the quasi-steady-state period with a recently obtained distribution (dashed line) that is believed to be still under the influence of the April 1982 eruption of E1 Chichon. WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN ATMOSPHERIC CONDUCTIVITY, SMALL ION CONCENTRATION, AND MOBILITY 30 The atmospheric conductivity depends on the exis tence of positive and negative ions, whereas the contri bution of free electrons can be neglected below about 45 km. There is normally a mixture of ions and the re sulting conductivity can be expressed in terms of the number densities and mobilities of the individual species as fir= (J+ + a_ = e~ni+ki+ + e~ni ki i i (12. 1) with e the electronic charge and n and k the number densities and mobilities of the particular positive and negative ions. The ion mobility is defined by the drift velocity v of the ions in an electric field E as v = kE (12.2) and depends on the mass, the collisional cross section, and charge of the individual ions (ions are believed to be singly charged in the lower atmosphere) as well as on the density and polarizability of the surrounding gas. It is inversely proportional to the air density and can be ex pressed by the reduced mobility ho as Kohl = k pot(h) (12.3) where pO and To are STP pressure and temperature (1013 mbar, 273 K) and p and T are pressure and tem perature at height h. An empirical relationship between reduced mobility and ion mass in nitrogen is given by Meyerott et al., (1980) and shown later in Figure 12.13. In the troposphere and lower stratosphere the atmo spheric conductivity is maintained by the so-called small ions with reduced mobilities around 1.5 cm2/V see, whereas the mobilities of large ions (charged aerosol particles or large molecular clusters) are too small to contribute directly to the conductivity (e.g., Israel, 1973b). As will be discussed later, large ions as well as attachment by aerosol particles can reduce the conduc tivity significantly. The production and annihilation of small ions is shown schematically in Figure 12.5. The molecular ion and remaining electron created by the io nizing process form charged molecular clusters (the small ions) after several reactions. These small ions are annihilated by mutual recombination and neutraliza tion, or they become almost immobile by attachment to aerosol particles or large ions. Under steady-state condi tions and assuming equal densities of positive and nega tive small ions, the fundamental balance equation be comes in its most simplified form dn/dt= 0 - q - an2- hnZ, (12.4)

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS MOLECULAR SMALL ION ION ~ (a ~HMENT ~ ( ) PARTICLE COSMIC RAY / ~ / RECOMBINATION GAS ~ ) HYDRATION AND DESTRUCTION GAS MOLECULES MOLECULE in\ OF HYDRATION SHELL i' ELECTRON \ ~ ~/AT T A C H M E N T go) A E RO ISCOLLE MOLECULAR SMALL ION ION where q is the ionization rate, ax the recombination coef ficient, ~ the attachment coefficient, and Z the aerosol concentration. An expression for (r) that is relevant to stratospheric conditions has been developed by Zikmunda and Mohnen (1972) and is approximately $(r) = 2.35 X 10-4 r]-457, where r is the radius of the aerosol particle in micrometers. Recombination coeffi cients were reported by Smith and Church (1977) and experimentally derived from nearly simultaneous bal loon measurements of the ionization rate, the small ion density, and the conductivity by Rosen and Hofmann (1981a, 1981b) and Gringel et al. (1983) . The atmospheric conductivity within balloon alti tudes is measured mostly with the Gerdien condenser in/km technique (e.g., Israel, 1973a). In contrast to ion density measurements, conductivity measurements are largely independent of the airflow rate through the Ger clien tube. This seems to be the main reason for the rela tively good agreement among different conductivity profiles as reported by Meyerott et al. (1980~. A direct comparison of three different Gerdien-type sondes has shown in fact an agreement of the resulting conductivity profiles within 10 percent to 32 km height (Rosen et al., 1982~. Figure 12.6 shows a mean profile (21 soundings) of the positive polar conductivity for quiet solar conditions and a geomagnetic latitude around 50 (Gringel, 1978~. This profile can be analytically expressed by the relation 3 cr + (TO - 14 mho/m) = expti Lo aizi), (12.5) with z the altitude (in kilometers) and an = 6.363 X 10-~, al = 3.6008 X 10-~, as = -8.605 X 10-4, and as = 1.0331 X 10-~. The scattering of the mean values as shown for kilo- meter intervals is considerably below 15 km, indicating a highly variable aerosol density throughout the tropos- phere. The noticeable increase of the conductivity 171 FIGURE 12.5 Schematic representation of the production and annihilation of atmo- spheric small ions. around 13 km can also be attributed to a sharp decrease of aerosol particle concentrations, especially condensa- tion nuclei, above the tropopause. For comparison, Figure 12.6 shows the mean of three conductivity measurements conducted within 1 week following solar flares. One profile was obtained on Au- gust 8, 1972, during a period of intense solar events. The other two flights were conducted 3 and 7 days, respec- tively, after a solar flare associated with an intense type- IV radio burst on April 11, 1978. For all three flights the 30 20 10 ~-- , , , A4~_ o 1 10 100 1000 polar conductivity At active sun X quiet sun FIGURE 12.6 Profiles of the positive polar conductivity versus alti- tude (a+ = a ) during quiet and active solar conditions. Mean values and standard deviations are shown for altitude intervals in kilometers (Gringel, 1978).

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172 ionization rate was appreciably reduced by the flare- related Forbush decrease, resulting in a remarkable conductivity reduction throughout the lower strato- sphere. For the August 8, 1972, flight the conductivity reduction reached deep into the troposphere (see also Figure 12.8 below). The ratio between the values of positive and negative polar conductivity exhibit a noticeable altitude depen- dence as shown in Figure 12.7 (Gringel, 1978~. In the troposphere the negative conductivity values exceed the positive ones by about 12 percent. Between 15 and 20 km both polarities are about equal, whereas above 20 to 25 km the negative conductivity becomes 5 to 10 percent smaller than the positive on the average. Assuming equal densities of positive and negative small ions, the same can be concluded for the corresponding average small-ion mobilities. As shown by Roble and Tzur (Chapter 15, this vol- ume) the vertical columnar resistance is an important parameter within the scope of the global atmospheric electrical circuit. This columnar resistance Rc is related to the atmospheric conductivity by he Rc= ~ (CJ+ + ~ Ah (12.6) J hi and denotes the resistance of a vertical air column with a 1-m2 base between the ground and the equalization in/km ]4 ~ 12 _ JO F 8 F 6 l I A+/A 1___ 1 1 1 1 1 1 ~ 0,6 0,8 1,0 FIGURE 12.7 The ratio of positive to negative polar conductivity as deduced from 10 balloon flights (Gringel, 1978~. WOLFGANG GRINGEL. NAMES M. ROSEN and DAVID T. HOFMANN 24 he ~ :2 _ 8 ~ ~ ~ , ~ ,,,'l ,~, ', ',,, o 5 lol6 1017 Qm2 An+ ~_( ~ - 691 ) +~+ :{ A-782 RC (hi) ~ +` 5: FIGURE 12.8 Mean columnar resistance [RC(h~] between the lower-altitude hi and 60 km. The profiles Rc+ (hi) are calculated from positive polar conductivity profiles only for quiet solar conditions (A + ) and after solar flares measured on August 8, 1972 (A-691) and on April 14, 1978 (A-782. layer. From Eq. (12.6) Rc is determined mainly by the low conductivity values near the ground. Figure 12.8 shows the columnar resistance RC(h~) between the lower height hi and 60 km as function of hi under quiet solar conditions as calculated from the conductivity profile in Figure 12.6 and using the ratio between positive and negative conductivity shown in Figure 12.7. The mean value from the ground to 60 km was found to be 1.3 X 10~7 Q m2 at Weissenau (South Germany, 450 m above sea level) during fair-weather conditions. The varia- tions are on the average about 30 percent and are caused by a changing ionization from radioactive materials near the ground and by varying aerosol concentrations in the lower troposphere. The first 2 km of the atmo- sphere contribute about 50 percent and the first 13 km about 95 percent to the total columnar resistance. The right side of Figure 12.8 shows three profiles of the positive polar columnar resistance R+ as a function of the lower height hi for quiet solar conditions and two profiles following solar flares. These three profiles were calculated using only positive conductivity values and therefore show about twice the value of the actual Rc obtained from both polarities. Whereas the Forbush de- crease observed on April 14, 1978, influenced mainly the part of the columnar resistance above the tropos- phere, the enhancement reached deep into the tropos- phere on August 8, 1972, at a geomagnetic latitude of 48. The part of RC above 13 km was found to be higher by 13 and 28 percent, respectively, when compared with RC obtained under quiet solar conditions. As pro- posed by Markson (1978) this could cause a reduction of the current flowing from the top of the thunderclouds to

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS the ionosphere, resulting in a lower value for the ionos- pheric potential reported for periods of high solar activ- ity by Fischer and Muhleisen (1972~. Layers of an increased aerosol density can signifi- cantly reduce the atmospheric conductivity owing to at- tachment of small ions on these aerosol particles. Figure 12.9, as an extreme, shows a conductivity profile through a Sahara dust layer between 1.7 and 3.7 km height and 2200 km west of the West African coast (Gringel and Muhleisen, 1978~. The dust concentration Z* responsible for the conductivity decrease is also shown. The authors report a mean mass concentration of 1200 g~ 3 throughout the layer. Owing to the low alti- tude of the layer the total columnar resistance was in- creased about 30 to 50 percent within these large-scale areas of Sahara dust transport across the North Atlantic. It is estimated that about the same increase of Rc occurs 40: km I 3OI 20 n km Ascent at Pos. 16,5N, 37 W to Launching 26.11.73 14.42 Gem h 10 km 5 o . . . . . ~i/ Z~'cm3 ~i- 46 - -*/ ,' - 127 6dA ~' -140 ~,, ~ 44 Sahara dust layer . . ., , I A 50 1~14 Q~1 - 1 10 FIGURE 12.9 Polar conductivity as a function of altitude and the concentration of mineral dust particles Z* derived from the conductiv- ity decrease ^X in the main Sahara dust transport layer at 2200 km distance from West Africa (Gringel and Muhleisen, 1978~. 173 ,~ Aster (1968) I ~uti (1966) h I _~ 0 5000 Ah 10 a) ~5) ~ . . 1 0000 cm~3 ~ Kroening (1960) ~ C) Paltridga . it, /' __' 10 _ ~~i' ( 1966) :~ OCR for page 166
174 authors as reported by Riekert (1971~. The profiles show large variations among each other and differ by almost a factor of 5 at the ion density maximum near 15 km. The small-scale fluctuations shown in the profiles of Kroen ing (1960) and Paltridge (1965) have been attributed to the attachment of small ions on particles. However, it is not clear that the known stratospheric aerosol size and concentration can quantitatively account for the re quired amount of ion depletion, except under rare cir- ~ 0.2 _ cumstances. O If, on the other hand, the airflow through the Ger- OCR for page 166
ELECTRICAL STRUCTURE FROM O TO 30 KILOMETERS entire altitude range. Following these measurements a balloonborne ion-mobility spectrometer was developed and for the first time was flown successfully at Laramie, Wyoming, on June 6, 1983 (Gringel, in preparation). The spectrometer consists of a voltage-stepped Gerdien condenser with divided collector electrode, force venti- lated by a lobe pump. The maximum electric-field strength is kept well below 1 V/cm Torr in order to avoid a breakup of the weakly bonded small ions. As prelimi- nary results, the fractional abundances of positive and negative small ions with respect to the reduced mobility are shown in Figures 12.13 and 12.14 for altitudes of 26 and 24.5 km, respectively. These results indicate that most of the positive ~ ~ 78 percent) and negative ~ ~ 90 percent) ions have reduced mobilities between ~ 1 and ~2.2 cm2/V sec. The mass-mobility relation by Mey- erott et at. (1980) indicates that most of the ions of both polarities have masses between 55 and 400 emu. Whereas only 20 percent of the negative ions show re- duced mobilities larger than ~ 1.7 cm2/V see, approxi- mately 43 percent of the positive ions exceed this value and have masses smaller than about 100 emu. The re 1 ' ' x 1 x xl IX W - 204 MAY 15, 1979 30 ye ~ 20 _ c, J 10 _ x 1 ko+= ( 1.35 + 0.08 ) cm2 V Is 1 x l x Ix x1x x 1 ,` 1 x lxx I x l xx x I x xx x xx xx Xl IX x - -4 1 1 ~ 1 1 1 1 rot ~ 1 O o 1111 1.0 kO.t,(cm2 V Is I ) 2.0 FIGURE 12.13 Reduced mobilities of positive small ions versus alti- tude calculated from simultaneous measurements of small-ion density and conductivity (Gringel et al., 1983). 175 NEGATIVE IONS: 30- 25 mb _ 2 Ko ~ 1.47cm /Vs 0.4 it m 0 3 ~ as At o ~0.2 fir 0.1 o 0.1 L AR AMIE, WY JUINE 7. 1983 ~r;: 1.0 REDUCED MOBILITY ( cm 2/Vs ) 10 FIGURE 12.14 Reduced mobility spectrum of negative ions around 24.5 km (Gringel, in preparation). duced average mobility values are 1.5 cm2/V see for the negative ions and 1.8 cm2/V see for the positive ions with an accuracy range of + 10 to - 20 percent. It cannot be decided at this time whether the reduced mobilities measured in 1979 (see Figure 12.13) and 1983 are really different from present values. The negative ion-mobility spectrum shown in Figure 12.14 is quite consistent with ion mass spectrometer measurements reported recently by Viggiano et al. (1983~. These authors found that the main mass peaks of negative ions between 125 and 489 emu be- long to the main ion families NO3 (HNO3)n and HSO4H2SO4)m(HNO3)n. The heavy HSO4 core ion family was found during their flights (September/Octo- ber 1981) mainly at altitudes above 30 km. However the major volcanic eruption of E1 Chichon in early April 1982 has changed the H2SO4 content of the stratosphere dramatically, as reported among others by Hofmann and Rosen (1983a, 1983b). Their aerosol measurements as well as the negative-ion mobility spectra indicate the presence of the heavy HSO 4 core ion family well below 30 km. In contrast to negative-ion mass spectrometer mea- surements, as of this writing the presence of positive ions having masses greater than 140 emu in the lower strato

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176 sphere (e.g., Arnold et al., 1981) have not been de tected. This is not consistent with ion-mobility measure- h meets and clearly needs further investigation. AIR-EARTH CURRENT AND ELECTRIC 10 FIELDS IN THE LOWER ATMOSPHERE The atmospheric electric circuit is characterized by a difference in voltage (on the order of 300 kV) between the highly conductive ionosphere (commonly referred to as the equalization layer) and the Earth's surface, which is also a relatively good conductor. This voltage Vat is thought to be maintained principally by thunderstorms acting as the generators and the atmospheric conductiv ity acting to discharge the ionosphere through continu ous flow of current. The value of this air-earth current density in fair-weather areas depends on the voltage Vat and the columnar resistance Rc and is, according to Ohm's law, iv= V~/Rc. (12.7) The value of the atmospheric electric field E(h) de pends on the air-earth current density and the electrical conductivity of the air according to the following Ohm's law relationship: Ah) = E(h) [~+ (h) + ~ Chid. Under steady-state conditions it is expected for rea- sons of continuity that the air-earth current density is constant with altitude if large-scale horizontally homo- geneous conditions exist and if no charged clouds or other disturbances alter the so-called fair-weather con- ditions. Figure 12.15 shows the atmospheric electric field and both polar conductivities as measured simultaneously over the North Atlantic by Gringel et al. (1978~. The field and conductivity profiles show clearly the inverse pattern to each other, which is expected for a constant air-earth current density through the atmosphere. Even a thin cloud layer at 6 km did not disturb this inverse pattern. The mean vertical air-earth current density for this particular balloon flight was calculated to be iv = (2.35 + O.1S) pA/m2, a typical value for our oceanic measurements. Another profile Of iv obtained at Lara- mie, Wyoming (Rosen et al., 1982) to 31 km height is shown in Figure 12.16. Again the profiles of both polar current densities show the expected constancy with alti- tude. At the same time of this flight at Laramie, the ionospheric potential Vat was determined over Weisse- nau, Germany, by integration of the measured electric- field strength (Fischer and Muhleisen, 1975) and found to be 330 kV, a value that should be the same as over Laramie according to the classical picture of the global WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN km 5 o ~ Lot _1 ~ _ -A. ~ )- _ _ , . . ~ A_ t~ ,_-' ~1'' r I A;J Gl l 1 2 5 10 20 50 O 5 _ E do; - 1 2 JV. ,_ i 1 1 1ol2 AL 2 1^ _ OX _ ~ Xk x? x.ExA. x, a. ExA_ x8x _ ALL X~ Xt _ I ~ _=, 1 ., 1. 1 _ E/Vm' 100 A/1~44~1m' FIGURE 12.15 Polar air-earth current densities iv+ and iv- versus altitude calculated from simultaneously measured electric-field strength E and both polaI: conductivities ()\ = a) over the North Atlan- tic (Gringel et al., 1978~. electrical circuit. In addition, the columnar resistance was obtained from an atmospheric conductivity profile and found to be RC = 0.65 X 1017 Q m2. This implies that the total conduction current density, calculated from VI and Rc, is S.1 pA/m2. The good agreement with the mean value calculated from the conductivity and elec- tric-field profiles proves that the Earth surface and the ionosphere can be regarded as good conductors where charges are distributed worldwide within short times. The fact that iv over Laramie shows about twice the value as over the Atlantic is explained by the high alti- tude of Laramie (2150 m above sea level) resulting in the low RC value given above. These 2 km normally contrib- ute about SO percent to the total columnar resistance of around 1.3 X 10~7 Q m2 between sea level and the iono- sphere. Direct measurements for the air-earth current density in the free atmosphere have been carried out also with long-wire antenna sondes described by Kasemir (19603. Whereas Ogawa et al. (1977) reported a constant air- earth current throughout the troposphere and lower stratosphere, the measurements by Cobb (1977) at the South Pole indicated a slight decrease of the iv values

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS above the tropopause. The reasons for this current de crease are unknown. At globally representative stations the air-earth cur- rent density shows a diurnal variation versus universal time with a minimum at around 0300 GMT and a maxi- mum near 1800 GMT, reflecting the diurnal variations of the ionospheric potential. Figure 12.17shows this di- urnal variation measured near the surface in the North Atlantic (Gringel et at., 1978) and near the ground at the South Pole (Cobb, 1977) during fair weather. The larger variation over the North Atlantic is probably due to the relatively short observation time of only 15 days. The agreement of the two curves also strongly supports the concept of an universally controlled global circuit. Direct-current density measurements near the ground at a continental station have been reported by Burke and Few (1978~. They observed a typical sunrise effect that is characterized by a gradual increase of the atmo- spheric conduction current within an hour after sunrise, reaching a peak about 2 hours after sunrise. The current density then gradually decreased but usually remained at a higher value than was observed before sunrise. This sunrise effect is thought to be caused by mechanical transport of positive charges following the onset of con 35 30 _ 25 _ ye - 20 _ ca ~ _ 10 5 _ O 1 1,,1 1 1 1 1 1 1 111 0.5 1 2 5 '"'1 1 1 1 1 1 1 1111 W - 186 x E x>+ o Ex x x o' 1 x Ol x J IX b olx olx Ix o IX Ix 1 o Xl x1 o 1 o x iv = ( 5 1+ 0.3) pA /ml2 1 _O iv+ (pA m ') FIGURE 12.16 Polar air-earth current densities iv+ and iv- mea- sured on August 4, 1978, at Laramie, Wyoming. The mean total air- earth current density is j' = (5.1 + 0.3) pA/m2. 140 Yo 120 ~ L . ,_ JV/]Y 100 i,""' 177 80 60 LO North Atlantic Jv ~ 2,9 pA/m2 26.10.73- 23.11.73 - South Pole: Jv. 2,5 pA/m2 Nov. 72 - March 74 oh 6h 12h 18 GMT 24h FIGURE 12.17 Mean diurnal variations of the air-earth current density in relative units over the North Atlantic (Gringel et al., 1978) and at the South Pole (Cobb, 1977~. vection. During fog they observed low values of iv that can be attributed to an enhancement of the columnar resistance, caused by the attachment of small ions to the fog droplets. Beneath low clouds without precipitation they usually found negative current readings, which are interpreted by Burke and Few (1978) as charge-separa- tion processes occurring in most of the low clouds, whether or not the clouds finally produced local precipi- tation or developed into thunderclouds. The electric field in the lower atmosphere is vertical and directed downward during fair-weather conditions and large-scale atmospheric homogeneity. In the litera- ture of atmospheric electricity, that direction is defined as the direction a positive charge moves in the electric field (e.g., Chalmers, 1967~. At globally representative stations, such as ocean or polar stations, the vertical co- lumnar resistance remains nearly constant during fair weather (Dolezalek, 1972~. Here the electric-field strength near the ground shows a diurnal variation with universal time similar to that shown for the air-earth current density in Figure 12.17, both reflecting varia- tions of the ionospheric potential. Over the continents consideration must be given to a varying ionization rate in the first few hundred meters caused by the exhalation of radioactive materials from the Earth. This ionization rate depends strongly on different meteorological pa- rameters, such as convection, and therefore the colum- nar resistance can no longer be regarded as constant. As shown by Israel (1973b) the global diurnal variation of the electric field is normally masked by local variations at these stations. If local generators, such as precipita- tion, convection currents, and blowing snow or dust,

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178 FIGURE 12.18 Typical variations of the vertical electric field near the ground and their relative amplitude distribution during fair weather (0), haze God, and fog ~-~ (from Fischer, 1977~. - > to - IL - J 0 1 2 TIME ( hr) _O ac o 7C 60 ~1 _ SO 0- ~40 AS - J ~0 to 10 o L -200 0 +200 also become active, the description becomes increas- ingly complicated and the vertical electric-field strength Ez can vary considerably. Figure 12.18 shows typical variations of Ez at a conti- nental mid-latitude station during fair weather and also during haze and fog (Fischer, 1977~. The relative occur- rence of the field amplitudes is also shown. During fair weather the variation is small with a mean value of Ez about 120 V/m with no negative fields. During haze and fog the variations become much larger and even nega- tive values of Ez occur indicating the presence of space charges around the station. The higher positive Ez val- ues are mainly caused by a drastic reduction of the at- mospheric conductivity due to the attachment of small ions to haze or fog droplets. The highest values of Ez are measured during rain or snow showers and thunderstorms as shown in Figure 12.19 (Fischer, 1977~. For both cases the amplitude dis- tribution shows a typical U pattern with mainly high positive or negative field values. The highest field values can reach 5000 V/m at the ground. This seems to be an upper limit because corona discharges build up a space- charge layer with the appropriate sign so as to reduce the original field values. Examples of anthropogenic in- fluences are shown in Figures 12.20 and 12.21. Figure WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN O -TYP .- TYP 400 500 200 +100 o -100 eon 70 60: SOL 40h Sol 2O 1O O - - - TYP 400 ~ ~'1~- 5 0 1 2 5 TIME ( hr ) 0 , 2 5 TIME ( hr ) n FAIR WEATHER 1 ~ 1 1 1 1 ll ll 1 1 r1 r.,R wE..~E~ - L 20 _ ~' so 60 ~0 ~0 so 1 1 1 1 1 1 1 1 1 1 1 1 1 1 - 200 0 ~ 200 - 200 0 + 200 ELECTRIC FIELD ( v/m ) 12.20 shows the undisturbed and disturbed electric- field values near the ground on the upwind and down- wind side of a high-voltage power line. Figure 12.21 shows the undisturbed and disturbed fields values near a large city in Germany (Fischer, 1977~. Whereas the sta- tion at the south shows almost a fair-weather field pat- tern, the values at the northern station exhibit large var- iations, and even negative values of Ez occur. The reasons for the large variations at the disturbed stations are in both cases drifting pollution and/or space charges. Above the ground the vertical electric field Ez drops rap- idly with increasing altitude owing to the increasing at- mospheric conductivity. Figure 12.22 shows the de- crease of the vertical electric field with altitude during fair weather, during cloudiness without precipitation, and during haze and fog as measured again over Weisse- nau, Germany (Fischer, 1977~. The positive sign of Ez means that the field vector is pointed downward again. The variations of different profiles, shown by the ha- chured areas, are mainly caused by conductivity varia- tions, especially in the lower troposphere, rather than by variations of the ionospheric potential itself. The scatter is greatly increased during periods of cloudiness and haze or fog, whereas the mean profile of the same 20 balloon flights (indicated by the thick curve in Figure

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS \7- TYP R-TYP J - - 40 IJJ C) 3 20 It' 3000 _ 2000 _ + 1000 _ O U t. - 1000 _ 2000 -1 1 0 1 TIME (hours) LL - ~- 200 0 +200 0 1 2 TIME (hours) 50 40 30 20 10 O 1 1 1 1 1 1 1 -200 0 +200 ELECTRIC FIELD ~ v/m ) FIGURE 12.19 Same as Figure 12.18 for rain or snow showers ~ v and for thunderstorms ~ ~ ~ (from Fischer, 1977). ]79 300 200 100 o can lo: can ~200 300 100 o _ 1 - 7h 8h gh lob ,, h ; I ~.v _ 7h oh 9 h 1oh Oh FIGURE 12.20 Influence of a high-voltage power line (220 kV) on the electric field near the ground (black station) compared with the electric field at the undisturbed station (Fischer, 1977). 12.22) still shows a pattern typical for fair-weather con- ditions. During rain or snow and especially in thunder- clouds, the scatter in the field values becomes much larger, including regions with large negative field val- ues. Temporal variations are fast, and the horizontal components of the electric-field strength can reach the same order of magnitude as the vertical components as measured by Winn et al. (1978~. These large variations of the electric-field strength in shower and thunder- clouds are caused by regions of high-space-charge den- sity of both signs in these clouds. Above the tropopause the vertical electric-field strength continues to decrease nearly exponentially as the atmospheric conductivity increases and normally drops to around 300 mV/m at 30 km at mid-latitudes. Holzworth and Mozer (1979) showed that solar proton events can cause large reductions of the stratospheric electric-field values at high latitudes by more than an

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180 FIGURE 12.21 Disturbed electric field near the ground in the neighborhood of a big city (black station). The electric-field pattern at the south is not disturbed and shows typical fair-weather values (Fischer, 1977~. Lid order of magnitude. The authors could explain their be- havior with the greatly enhanced ionization by solar protons, which in turn enhances the stratospheric con- ductivity and thereby reduces the local electric fields. CONCLUSION Galactic cosmic rays are the primary source of ioniza- tion in the lower atmosphere. They control the bulk at- mospheric conductivity parameter, which in turn is lin- early related to the small-ion concentration and small-ion mobility. Although the existence of a solar- induced modulation of the ionization rate and of the at- mospheric conductivity is evident, the basic physical mechanisms are not fully understood. More measure WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN 300 O . 11 h 12 h 13 h 14h 15h 200 ~If, 0 1 2 3 4 5km h 12h 13h 14h 15h AUGSBURG meets of both parameters (if possible simultaneously) are desirable in order to establish cyclic and transient solar modulation effects. The accuracy of direct mea- surements of small-ion concentrations and mobilities have shown improvements, but the results among dif- ferent researchers are still contradictory. Almost noth- ing is known about the mobility distribution of atmo- spheric ions throughout the troposphere and lower stratosphere. The existence of heavy ions with masses of several hundred emu, as inferred from mobility mea- surements, has only just recently been established by mass spectrometer measurements. Problems with the sampling procedure employed can not be overlooked. Simultaneous measurements of ion masses, ion concen- trations, and ion mobilities, together with conductivity ELECTRIC FIELD ( v/m ) FIGURE 12.22 The atmospheric electric field versus altitude during fair weather (O), cloudiness without precipitation (a), and during haze and fog (c=, - ). The black curves show typical measurements, the white curves show mean profiles and the hachured areas show the scattering of the values (Fischer, 1977).

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ELECTRICAL STRUCTURE FROM 0 TO 30 KILOMETERS and aerosol measurements, are clearly needed to gain a deeper insight into the physics and chemistry of atmo- spheric ions. Volcanic eruptions can result in a rather dramatic increase of the aerosol content of the lower at- mosphere. The extent to which these aerosols directly affect the atmospheric conductivity, small-ion concen- tration, and mobility should be investigated to a greater extent. On the other hand, the sulfuric acid content of the lower atmosphere is also drastically enhanced fol- lowing volcanic eruptions and might considerably influ- ence the ion composition. Air-earth current-density measurements seem to be consistent with the classical picture of the global circuit with some exceptions. The question of whether there are other global generators in the lower atmosphere in addition to thunderstorms could probably be unraveled by ground-based and bal- loonborne current measurements at different locations. The electric-field strength in the lower atmosphere, which is closely related to the air-earth current and the atmospheric conductivity, can undergo considerable fluctuations near the ground owing to conductivity vari- ations and the influence of a local generator. REFERENCES Arnold, F. (1983). Ion nucleation-A potential source for strato- spheric aerosols, Nature 299, 134-137. Arnold, F., and Th. Buhrke (1984~. New H2SO4 and HSO3 vapor mea- surements in the stratosphere-Evidence for a volcanic influence, Nature 301, 293-295. Arnold, F., G. Henschen, and E. E. Ferguson (1981~. Mass spectrome- ter measurements of fractional ion abundances in the strato- sphere-Positive ions, Planet. Space Sci. 29, 185-193. Barouch, E., and L. F. Burlaga (1975~. Causes of Forbush decreases and other cosmic ray variations, J. Geophys. Res. 80, 449-456. Burke, H. K., and A. A. Few (1978~. Direct measurements of the at- mospheric conduction current, J. Geophys. Res. 83, 3093-3098. Chalmers, J. A. (1967~. Atmospheric Electricity, Pergamon Press, London. Cobb, W. E. (1977~. Atmospheric electric measurements at the South Pole, in Electrical processes in Atmospheres, H. Dolezalek and R. Reiter, eds., Steinkopff, Darmstadt, pp. 161-167. Dolezalek, H. (1972~. Discussion of the fundamental problem of atmo- spheric electricity, Pure Appl. Geophys. 100, 8-43. Duggal, S. P., and M. A. Pomerantz (1977~. The origin of transient cosmic ray intensity variations, J. Geophys. Res. 82, 2170-2174. Fischer, H. J. (1977). Das luftelektrische Feld in Abhangigkeit von Luftverunreinigung und Wetterlage, Prometheus 7/2, 4-12. Fischer, H. J., and R. Muhleisen (1972~. Variationen des Ionospharen- potentials und der Weltgewittertatigkeit im 11-jahrigen solaren Zyklus, Meteorol. Rundsch. 25, 6-10. Fischer, H. J., and R. Muhleisen (1975~. A method for precise determi- nation of the voltage between ionosphere and ground, Report, As- tron. Inst., Universitat Tubingen, FRG. Forbush, S. E. (1954~. World-wide cosmic-ray variations, 1937-1952, J. Geophys. Res. 59, 525-542. Gringel, W. (1978). Untersuchungen zur elekrischen Luftleitfahigkeit unter Berucksichtigung der Sonnenaktivitat und der Aerosolteil- chenkonzentration his 35 km Hohe, Dissertation, Universitat Tu- bingen, FRG. Gringel, W., and R. Muhleisen (1978~. Sahara dust concentration in the troposphere over the North Atlantic derived from measurements of air conductivity, Beitr. Phys. Atmos. 51, 121-128. Gringel, W., J. Leidel, and R. Muhleisen (1978~. The air-earth cur- rent density at the water surface and in the free atmosphere above the ocean, Meteor Forschungsergebn. Reihe B 13, 41-52. Gringel, W., D. J. Hofmann, and J. M. Rosen (1983~. Measurements of mobility, small ion recombination and aerosol attachment coeffi- cients to 33 km, unpublished manuscript. Gringel, W., D. J. Hofmann, and J. M. Rosen (1984~. Stratospheric conductivity reductions related to E1 Chichon aerosol layers, pre- sented at the VII International Conference on Atmospheric Elec- tricity. Heaps, M. G. (1978~. Parameterization of the cosmic ray ion-pair pro- duction rate above 18 km, Planet. Space Sci. 26, 513-517. Hofmann, D. J., and J. M. Rosen (1979~. Balloon-borne measure- ments of atmospheric electrical parameters. I: The ionization rate, Atmos. Phys. Rep. AP-54, Univ. of Wyoming, Laramie. Hofmann, D. J., and J. M. Rosen (1983a). Stratospheric sulfuric acid fraction and mass estimate for the 1982 volcanic eruption of E1 Chi- chon, Geophys. Res. Lett. 10, 313-316. Hofmann, D. J., and J. M. Rosen (1983b). Sulfuric acid droplet forma- tion and growth in the stratosphere after the 1982 eruption of E1 Chichon, Science 222, 325-327. Hofmann, D. ]., J. M. Rosen, T. J. Pepin, and R. G. Pinnick (1975~. Stratospheric aerosol measurements I: Time variations at northern mid-latitudes, J. Atmos. Sci. 32, 1446-1456. Hogan, A. W., and V. A. Mohnen (1979~. On the global distributions of aerosols, Science 205, 1373-1375. Holzworth, R. H., and F. S. Mozer (1979~. Direct evidence of solar flare modification of stratospheric electric fields, J. Geophys. Res. 84'363-367. Israel, H. (1973a). Atmospheric Electricity, Vol. I, Israel Program for Scientific Translations, Jerusalem. Israel, H. (1973b). Atmospheric Electricity, Vol. II, Israel Program for Scientific Translations, Jerusalem. Junge, C. E. (1963~. Air Chemistry and Radioactivity, Academic Press, New York. Kasemir, H. W. (1960~. A radiosonde for measuring the air-earth cur- rent density, USASRDL Tech. Rep. 2125. Kroening, J. L. (1960~. Ion density measurements in the stratosphere, J. Geophys. Res. 65,145-151. Markson, R. (1978~. Solar modulation of atmospheric electrification and possible implications for the sun-weather relationship, Nature 273, 103-109. Meyerott, R. E., J. B. Reagen, and R. G. Joiner (1980~. The mobility and concentration of ions and the ionic conductivity in the lower stratosphere, J. Geophys. Res. 85, 1273-1278. Mitchell, J. D., R. S. Sagar, and R. S. Olsen (1977~. Positive ions in the middle atmosphere during sunrise conditions, Rep. ECOM-5819, U.S. Army Electron. Command, Fort Monmouth, N.J. Morita, Y., H. Ishikawa, and M. Kanada (1971~. The vertical profiles of the small ion density and the electric conductivity in the atmo- sphere up to 19 km, J. Geophys. Res. 76, 3431-3436. Neher, H. V. (1961). Cosmic-ray knee in 1958, J. Geophys. Res. 66, 4007-4012. Neher, H. V. (1967~. Cosmic ray particles that changed from 1954 to 1958 to 1965, J. Geophys. Res. 72, 1527-1539. Ogawa, T., Y. Tanaka, A. Huzita, and M. Yasuhara (1977~. Three dimensional electric fields and currents in the stratosphere, in Elec

OCR for page 166
182 trical Processes of Atmospheres, H. Dolezalek and R. Reiter, eds., Steinkopff, Darmstadt, pp. 552-556. Paltridge, G. W. (1965). Experimental measurements of the small ion density and electrical conductivity of the stratosphere, J. Geophys. Res. 70, 2751-2761. Patterson, E. M., and D. A. Gillette (1977~. Commonalities in mea- sured size distribution for aerosols having a soil-derived component, J. Geophys. Res. 82, 2074-2081. Pierce, E. T., and A. L. Whitson (1964~. The variation of potential gradient with altitude above ground of high radioactivity, J. Geophys. Res. 69, 2895-2898. Pinnick, R. G., I. M. Rosen, and D. I. Hofmann (1976~. Stratospheric aerosol measurements III: Optical model calculations, J. Atmos. Sci. 33, 304-314. Pollack, I. B., O. B. Toon, E. F. Danielson, D. J. Hofmann, and I. M. Rosen (1983~. The E1 Chichon volcanic cloud: An introduction Geophys. Res. Lett. 10, 989-992. Riekert, H. (1971~. Untersuchungen zur Beweglichkeit der Kleinionen in der freien Atmosphere, Dissertation, Universitat Tubingen, FRG. Rosen, J. M., and D. J. Hofmann (1981a). Balloon borne measure- ments of the small ion concentration, J. Geophys. Res. 86, 7399- 7405. Rosen, I. M., and D. J. Hofmann (1981b). Balloon borne measure- ments of electrical conductivity, mobility, and the recombination coefficient, J. Geophys. Res. 86, 7406-7410. Rosen, I. M., and D. J. Hofmann (1983~. Unusual behavior in the condensation nuclei concentration at 30 km, J. Geophys. Res. 88, 3725-3731. WOLFGANG GRINGEL, JAMES M. ROSEN, and DAVID J. HOFMANN Rosen, J. M., D. J. Hofmann, and K. H. Kaselau (1978a). Vertical profiles of condensation nuclei, J. Appl. Meteorol. 17, 1737-1740. Rosen, I. M., D. J. Hofmann, and S. P. Singh (1978b). A steady-state aerosol model, J. Atmos. Sci. 35, 1304-1313. Rosen, J. M., D. J. Hofmann, W. Gringel, J. Berlinski, S. Mich- nowski, Y. Morita, T. Ogawa, and D. Olson (1982~. Results of an international workshop on atmospheric electrical measurements, J. Geophys. Res. 87,1219-1227. Russell, P. B., T. J. Swissler, M. P. McCormick, W. P. Chu, J. M. Livingston, and T. J. Pepin (1981~. Satellite and correlative mea- surements of the stratospheric aerosol I: An optical model for data conversions, J. Atmos. Sci. 38, 1279-1294. Smith, D., and M. I. Church (1977~. Ion-ion recombination rates in the Earth's atmosphere, Planet. Space Sci. 25,433-439. Viggiano, A. A., H. Schlager, and F. Arnold (1983~. Stratospheric negative ions-Detailed height profiles, Planet. Space Sci. 31, 813- 820. Widdel, H. U., G. Rose, and R. Borchers (1976~. Experimental results on the variation of electrical conductivity and ion mobility in the mesosphere,1. Geophys. Res. 81, 6217-6220. Willeke, K, and K. T. Whitby (1975~. Atmospheric aerosols: Size dis- tribution interpretation, J. Air Pollut. Control Assoc. 25, 529-534. Winn, W. P., C. B. Moore, C. R. Holmes, and L. G. Byerley III (1978). Thunderstorm on July 16, 1975, over Langmuir Labora- tory: A case study, J. Geophys. Res. 83, 3079-3092. Zikmunda, I., and V. A. Mohnen (1972~. Ion annihilation by aerosol particles from ground level to 60 km height, Meteorol. Rundsch. 25, 10-14.