Observing Weather and Climate from the Ground Up A Nationwide Network of Networks (2009) / Chapter Skim
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4 Observing Systems and Technologies: Successes and Challenges
4 Observing Systems and Technologies: Successes and Challenges
Pages 87-129
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From page 87... ...
mesoscale observations are embedded. The global context is important because, for many applications, the utility of limited-area mesoscale observations is highly dependent on larger domains of observations, for example, in the provision of initial and boundary conditions for mesoscale numerical weather prediction models.
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From page 88... ...
Networks for Surface Observations: Land-Based Most commonly, "surface" measurements consist of temperature and relative humidity, wind, precipitation, and air pressure. World Meteorological Organization (WMO)
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From page 89... ...
However, such non-representativeness on the synoptic scale is strong evidence of value at the mesoscale and is the primary driver for such extensive private and public investment in surface stations nationwide. Likewise, data from individual homes and schools may not meet the accuracy standards or exposure criteria that are required for numerical weather prediction or research.
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From page 90... ...
bitmap image While the technology for many of the "weather" variables is mature, measurement of rainfall and especially surface snowfall and precipitation type remains a challenge. Rainfall measurements from gauges are reasonably accurate, but rainfall varies on scales smaller than the typical spacing between gauges; this problem has been alleviated to some degree by combining gauge and weather radar measurements.
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From page 91... ...
While networks that collect weather data can be dense, as illustrated in Figure 4.1, networks that collect soil moisture can seem sparse by comparison, as illustrated in Figure 4.2. A notable exception is the Oklahoma Mesonet (see Box 4.1)
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From page 92... ...
, air pressure, precipitation, incoming solar radiation, and soil temperature at 10 cm either below natural cover or bare ground. Most sites also sample air temperature at 9 m above ground, wind speed at 2 and 9 m above ground, soil moisture at 5, 25, and, 60 cm below ground, soil temperatures at 5 and 30 cm below ground under the natural sod cover, and soil temperature at 5 cm below bare ground.
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From page 93... ...
While not especially useful for numerical weather prediction, cameras are highly useful for road transportation, providing drivers and road managers a check on road conditions (weather, traffic flow, state of the road due to precipitation) , and for monitoring wind and weather changes in other applications, such as fighting forest fires or warning about the spread of noxious substances.
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From page 94... ...
SOURCE: Nationalbitmap image http://www.ndbc.noaa.gov/. Data Buoy Center, U.S.
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From page 95... ...
Figure from National Data Buoy Center, http://www.ndbc.noaa.gov/.
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From page 96... ...
The vertical resolution of the measurements is good, better than 10 hPa. The roughly 80 U.S.
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From page 97... ...
The profiles, along with cloud liquid water path are derived at roughly 5-minute intervals. GPS Integrated Precipitable Water. An analysis of GPS signal delays that result from the radio refractive index profile leads to estimates of (columnar)
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From page 98... ...
98 FIGURE 4.6 The surface-based GPS network in the United States. 4-7.eps 2 bitmap images BROADSIDE
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From page 99... ...
array in Oklahoma, where it can be ingested into experimental Numerical Weather Prediction (NWP) models used to predict severe storms.
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From page 100... ...
techniques or echo tracking. Because backscatter from insects is significant in otherwise clear air, such information is typically available for the boundary layer when the temperature is above 10 °C.
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From page 101... ...
OBSERVING SYSTEMS AND TECHNOLOGIES 101 FIGURE 4.7 Current U.S. WSR-88D coverage and the gap in coverage generated by 4-8.eps the Earth's curvature.
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From page 102... ...
Cloud radars are used to research clouds, tornadoes, and the clearair boundary layer. Radar wind profilers.
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From page 103... ...
The sharp drop in signal at the top of the convective boundary layer is used to estimate its depth; however, estimates of the depth of the night-time boundary layer are more difficult due to its shallowness. Boundary-layer depth is a major source of uncertainty in the predictive capability of current numerical chemical forecast models.
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From page 104... ...
and reflect from inhomogeneities in the density structure of the atmosphere, prevalent at temperature inversions. From the time of flight of the emitted pulse and the returned reflected sound, one can determine range to the height of the planetary boundary layer (PBL)
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From page 105... ...
. The transponder emits sound waves, whose propagation speed is detected by the Doppler radar at various ranges, thus enabling estimates of the virtual temperature profile.
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From page 106... ...
This allows determination of relative humidity profiles, if a temperature profile is available. Similarly, the ratio of the elastic aerosol channel signal to the Raman nitrogen signal gives the aerosol mixing ratio, and, by taking a derivative of this ratio with range, the extinction of the aerosol can be measured precisely with no assumptions about the aerosol (in contrast to the elastic systems discussed above)
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From page 107... ...
FIGURE 4.10 Simultaneous observations of lidar planetary boundary-layer heights from four REALM lidar stations from Virginia to New York City on December 4, 2006. 4-11.eps 107 bitmap image enlarged for broadside
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From page 108... ...
Automated Aircraft Reports The ACARS (Aircraft Communications Addressing and Reporting S ystem) program was initiated in the 1970s by NOAA and the FAA to put temperature and wind sensors on the shells of commercial aircraft.
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From page 109... ...
has been used to profile ozone, carbon monoxide, water vapor, and nitrogen oxides upon takeoffs and landings of commercial aircraft in Europe, Asia, and North America. The measurements have allowed determination of seasonal differences in the ozone column, detection of stratospheric air versus tropospheric sources, and some long-term trends in ozone measurements.
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From page 110... ...
. It might also be possible to move a fleet of mobile radar wind profilers into a region threatened by hurricanes.
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From page 111... ...
/NCAR, the Mobile Cross-Chain Loran Atmospheric Sounding System [MCLASS] operated by the National Severe Storms Laboratory [NSSL]
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From page 112... ...
Satellites also provide information on surface characteristics such as vegetation and soil moisture, both of which have been shown to be important to storm initiation and the prediction of convective weather. Satellite orbits can be divided into two types, geostationary orbits and low-Earth orbits.
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From page 113... ...
on the Terra and Aqua polar-orbiting satellites uses infrared radiation to retrieve vegetation characteristics, which are used as input into the landsurface models embedded in experimental numerical weather prediction models. Satellite images such as GOES, the Advanced Very High Resolution Radiometer (AVHRR)
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From page 114... ...
mission is returning very high vertical resolution images of clouds and aerosols. These active sensors promise to be able to retrieve data well down into the lower troposphere with high resolution, which is of value to the mesoscale observations of this study.
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From page 115... ...
The CPR profiles clouds along the satellites ground track with a horizontal resolution of 2 km while providing information with 500-m vertical resolution on cloud water and ice concentrations, cloud thickness and cloud base and top height. CloudSat and CALIPSO are flying in a formation called the "A-Train" with Aqua, PARASOL,10 and Aura.
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From page 116... ...
, and it is difficult, if not impossible, to untangle the planetary boundary-layer information from those profiles. Many sensors, designed to give many levels of vertical resolution, have not lived up to billing and give only one or two pieces of independent information, which tend to peak higher in the troposphere than would be useful for planetary boundary-layer application.
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From page 117... ...
Considering the importance of water storage in the snowpack and reservoirs and hydroelectric power generation, and the danger of traveling in the winter or fighting forest fires in the summer, the needs for observations in the mountains go beyond those for weather forecasting alone. Coastlines and cities, both of which have high concentrations of people, also take on special importance, particularly when one considers the need for observations to respond to a release of toxic substances, to treat the roads in response to an ice storm or blizzard, or to evacuate people in advance of hurricane landfall.
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From page 118... ...
Improving our capabilities requires special consideration of the urban environment and the "urbanization" of our meteorological measurement and modeling components. Recent studies are showing that improvements in NWP and air quality dispersion require better descriptions of urban surface fluxes and the vertical structure of the urban boundary layer (Baklanov et al., 2006)
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From page 119... ...
Figure 4.11 shows a conceptual deployment scenario of low-cost microwave radar sensors in an urban environment where the radar antenna panels are attached to the edges of the taller buildings. The electronic-scanning sensors merge seamlessly with the background and have no moving parts (McLaughlin et al., 2007)
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From page 120... ...
They present the danger of slick roads, high winds, poor visibility, and avalanches, rockfalls, and mudslides. They also cause significant downstream effects in weather and stream flow, the latter causing water resource management challenges up to 1000 km.
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From page 121... ...
The Planetary Boundary Layer Challenge One of the most difficult to measure and yet one of the most important parameters is the height of the daytime and nighttime planetary boundary layer (PBL)
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From page 122... ...
However, the characteristic spacing of radar wind profilers is too large, often missing medium-sized mesoscale circulations that spawn disruptive and severe weather. The number of commercial airline observations has a large-amplitude diurnal cycle, which deprives the composite observing system of needed data for ~8 hours per day and leaves the system vulnerable during large storms (or terrorist attacks)
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From page 123... ...
. Yet, there is no national coverage of sufficient scope to address the planetary boundary-layer challenge.
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From page 124... ...
has identified a path forward for the next generation Earth observational satellite system for the United States. Measurements that are relevant to mesoscale applications include soil moisture using the L-band, soil composition and vegetation characterization from a hyperspectral spectrometer, columns of atmospheric trace gases to high horizontal resolution, aerosol and cloud profiles, land-surface topography, temperature and humidity soundings, tropospheric winds that don't depend on feature tracking (from Doppler lidar)
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From page 125... ...
Finding: It is a national imperative to sustain and improve operational geostationary satellite observations as a critical adjunct to the surface based mesoscale network. Observations from geostationary orbit are unique and inherently Mesoscale, owing to the high rate of time domain sampling and excellent horizontal resolution.
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From page 126... ...
Recommendation: As a high satellite instrument priority, NASA and NOAA, in cooperation with foreign space agencies, should seek to improve the quality of geostationary satellite water vapor and tempera ture soundings within continental atmospheric boundary layers. Infrared hyperspectral soundings and soundings from microwave synthetic thinned aperture arrays, each in geostationary orbit, offer unique opportunities to improve mesoscale prediction.
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From page 127... ...
Upper air observations are provided mainly by land-based radiosonde and aircraft data, with a limited number of observations from ground-based wind profilers and radiosonde releases from ships at sea. Close to 900 land-based upper air stations provide radiosonde soundings to the GOS twice a day: at 1200 and 0000 UTC.
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From page 128... ...
are working to optimize AMDAR ascent and descent data for use by EUCOS member countries. For example in 2006, EUMETNET-AMDAR provided approximately 750 soundings per day.21 The RBSN observing stations and conventional upper air network do not all report on a routine basis, with the performance varying greatly by WMO region.22 Reports from stations over the United States are very reliable.
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From page 129... ...
Future research missions will continue to contribute to the space-based component of the GOS while influencing its evolution. Those planned research missions include investigations of atmospheric chemistry and trace gases, the Earth's gravity field, soil moisture and ocean salinity, atmospheric winds using lidar, disaster and environmental monitoring, integrated atmospheric column water vapor, cloud ice content, cloud droplet properties and distribution, aerosols, and polar ice and snow water equivalent.
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