4
Emerging Weather Research and Transitional Needs

Several research and transitional needs have come to be recognized in the United States as increasingly important but are only in the early stages of understanding or implementation. The committee refers to these as emerging weather research and transitional needs—in contrast to the established needs discussed in Chapter 3. Three high-priority emerging needs were identified in the 2009 BASC Summer Study workshop and subsequent committee meetings. The three emerging needs discussed here include very high impact (VHI) weather, urban meteorology, and renewable energy production.

The reader may wonder why VHI weather is included here as an emerging need rather than in the preceding chapter as one of several established needs. The answer lies in the emphasis here on impact forecasting rather than the traditional focus on weather prediction per se. Urban meteorology was recognized in the United States in the 1960s as an important topic, and much seminal urban meteorological research was conducted until the early 1980s when it was abruptly deemphasized as a research priority. A reemphasis on the meteorology of the urban zone and its societal import began again in the 1990s and continues today. In contrast, Europe has focused steadily on urban issues for many decades, as has Japan. Lastly, the meteorological challenges associated with the special needs of the renewable energy industry have come into sharp focus over the past 5 or so years. In all three emerging areas, much remains to be done. As mentioned previously, virtually all research and R2O needs have both established and emerging aspects, and so many of the challenges and needs cited in Chapter 3 are relevant as well, and are closely coupled to those discussed here in Chapter 4.

VERY HIGH IMPACT WEATHER

Weather-related disasters result in loss of life and disruption of communities as well as billions of dollars in damages in the United States an-



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4 Emerging Weather Research and Transitional Needs several research and transtonal needs have come to be recognzed n the Unted states as ncreasngly mportant but are only n the early stages of understandng or mplementaton. the commttee refers to these as emerg- ing weather research and transtonal needs—n contrast to the establshed needs dscussed n chapter 3. three hgh-prorty emergng needs were den- tfied n the 2009 BAsc summer study workshop and subsequent commttee meetngs. the three emergng needs dscussed here nclude very hgh mpact (VHI) weather, urban meteorology, and renewable energy producton. the reader may wonder why VHI weather s ncluded here as an emerg- ng need rather than n the precedng chapter as one of several establshed needs. the answer les n the emphass here on mpact forecastng rather than the tradtonal focus on weather predcton per se. Urban meteorology was recognzed n the Unted states n the 1960s as an mportant topc, and much semnal urban meteorologcal research was conducted untl the early 1980s when t was abruptly deemphaszed as a research prorty. A reempha- ss on the meteorology of the urban zone and ts socetal mport began agan n the 1990s and contnues today. In contrast, europe has focused steadly on urban ssues for many decades, as has Japan. Lastly, the meteorolog- cal challenges assocated wth the specal needs of the renewable energy ndustry have come nto sharp focus over the past 5 or so years. In all three emergng areas, much remans to be done. As mentoned prevously, vrtu- ally all research and R2o needs have both establshed and emergng aspects, and so many of the challenges and needs cted n chapter 3 are relevant as well, and are closely coupled to those dscussed here n chapter 4. VERy HIGH IMPACT WEATHER Weather-related dsasters result n loss of lfe and dsrupton of com- muntes as well as bllons of dollars n damages n the Unted states an- 89

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90 90 WHen WeAtHeR MAtteRs nually. Between 1980 and 2009 there were 96 major dsasters caused by VHI weather events that resulted n losses exceedng 1 bllon dollars each (ncDc, 2010). It goes almost wthout sayng that there s a great need for accurate forecasts and warnngs of severe, hazardous, and dsruptve weather condtons so that the resultng economc and socetal mpacts can be mnmzed. VHI weather can be defined as weather that endangers publc health and safety or causes sgnficant economc mpacts. VHI weather generally falls nto two categores: 1. severe and dsruptve weather hazards—ncludng tropcal storms and hurrcane-nduced extreme wnds, ran, and storm surges; severe thunder- storms and tornadoes; lghtnng; flash floods; ce and snow storms; dense fog; and wldfires—whch change rapdly on the tmescale of mnutes to hours or a few days; and 2. persstent weather hazards—ncludng long-lastng heat/cold waves; drought; and floodng due to persstent ran events—whch occur on longer tmescales of days to weeks or even years (e.g., drought). Advancng the understandng, montorng, and predcton of VHI phe- nomena requres mprovng the accuracy and tmelness of observatons, forecasts, and warnngs n order to develop an efficent response system that helps mnmze and mtgate the mpacts of hazardous weather. An expan- son n emphass from weather predcton alone to the predcton of weather and related mpacts s warranted. ths would necesstate development of new modelng and observatonal tools, nnovatve forecast gudance prod- ucts, and methods of nformaton and warnng dssemnaton to decson makers and stakeholders. Accordngly, new research and R2o prortes for VHI weather need to be establshed. Also requred s the close collaboraton of physcal and socal scentsts n settng prortes and developng effectve research and mplementaton programs. socal scentsts, especally, wll also play a crtcal role n developng o2R needs and prortes. to facltate a rapd R2o transton, t s crtcal to tran a new generaton of researchers, forecasters, and decson makers n the need for, and use of, a fully ntegrated forecast and response system. Current State of Affairs and New Opportunities Weather research over the past several decades has led to many ad- vances n montorng, understandng, and predctng VHI weather, whch

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 91 have contrbuted to major mprovements n forecasts and warnngs such as more accurate hurrcane tracks and longer lead tmes for tornadoes and severe thunderstorms. Although the number of VHI weather phenomena s extensve, ths secton ams to llustrate the varety of phenomena that have major mpacts on socety and dentfy emergng needs and opportuntes for weather research to better serve crtcal socetal needs. A number of prevous studes (table 1.1) by the U.s. Weather Research Program (UsWRP; e.g., emanuel et al., 1995) and the natonal Research councl (e.g., nRc, 1998b) can serve as benchmarks for comprehensve revews, because they dentfied many pressng needs and opportuntes for atmospherc, hydrologc, and related research and development that stll exst today. A New Impacts Paradigm the atmospherc communty has for many years worked dlgently to mprove the accuracy and resoluton n space and tme of the raw quanttes predcted by numercal models, such as temperature, humdty, wnd, and precptaton. statstcal technques have been used to predct addtonal quanttes and to ntroduce probablty of precptaton and other derved forecast parameters. Wth some exceptons, users have largely taken these weather predctons and used them n ther own decson support and rsk management processes. However, ths approach has not always produced the desred or optmal outcome, especally when complex weather forecasts are dfficult to understand and yet requre publc acton n response to the forecast. For nstance, probablstc forecasts of a landfallng hurrcane’s track and ntensty, wthout specfic mpact nformaton such as tmng and loca- ton of storm surge, extent of floodng, extreme wnds, and power outages, are nsufficent for effectve responses from emergency managers. A new paradgm for the comng decades s for end users and scentsts (both physcal and socal scentsts) to work together toward also provdng mproved, explct impact forecasts as well as advancng human comprehen- son of complex nformaton. the paradgm shft from forecastng weather to forecastng weather and mpacts wll challenge the tradtonal weather fore- castng approach and demand a full ntegraton of the physcal scences wth the socoeconomc scences that s relevant to weather mpacts and socetal and envronmental responses. Because of the mplcatons for publc safety and economc reslence, VHI weather phenomena are key targets for such ntegratve research and the transton of research results to operatons. As one example, consder the nformaton n Fgure 4.1, comparng tradtonal portrayals of weather forecastng, and the potental for mpacts

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92 92 WHen WeAtHeR MAtteRs FIGURE 4.1 Schematic representation of the paradigm shift from weather forecasting to impacts forecast- ing. At upper right and lower right are traditional depictions of predicted hurricane paths, wind and wave height swaths, rain, and satellite and radar observations. At lower left are radar observations and numeri- cal-model radar renditions of a hurricane. The figure in the upper left illustrates the new impacts paradigm, which predicts areas of power outages and restoration times. SOURCE: Shuyi Chen, committee member. forecastng. tradtonally, data from surface-based observng systems, recon- nassance arcraft, and satelltes are used n numercal weather predcton (nWP) models to make predctons about a hurrcane’s trajectory, ntensty (wnd speed), and precptaton. In the new, mpacts forecastng paradgm, these models would be used n conjuncton wth decson support models to yeld projectons of possble mpacts such as the extent of power outages and the tme to power restoraton for the regon affected by the hurrcane. In fact, there are prvate weather and rsk management companes that are now workng wth electrc utltes, nsurance and rensurance companes, and others to make ndustry-specfic mpact predctons for a varety of severe weather events. However, mpact predcton remans to be mplemented

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 93 more wdely—not only by the prvate sector but also by the publc sector wth ts responsblty to support and protect publc health and safety. one key component of, and a major challenge for, the predcton of mpacts s to more fully explot the capabltes of ensemble modelng of the atmosphere to produce probablstc forecasts of atmospherc quant- tes, and for these to then be used to generate probablstc forecasts of the mpacts and rsks of pendng VHI weather stuatons, thereby enablng mproved decson makng. Rather than the meteorologcal communty and the end-user communtes workng separately, teams of atmospherc sc- entsts, socal scentsts, and professonals from user groups1 need to work together to define the needed observatons and the desred predcted mpact parameters. ths approach has been recommended for hydrometeorologcal forecastng (Krzysztofowcz, 1998) n a semnal paper on the development and applcaton of jont decson-makng probabltes of rver stage predc- tons and user rsk tolerances. Severe and Disruptive Weather Hazards Hurricanes and Tropical Storms Although there has been sgnficant mprovement n hurrcane track forecasts, progress has been mnmal wth regard to storm ntensty forecasts. the mprovement n track forecasts s largely attrbuted to the advancement n satellte and dropwndsonde observatons (Frankln et al., 2003) over the oceans and model mprovement and data assmlaton n global models over the past few decades. Lmtng factors for hurrcane ntensty forecasts nclude the lack of understandng of rapd changes n storm structure and ntensty, routnely (and contnuously) avalable n stu observatons, and hgh-resoluton coupled ar–sea–land models (chen et al., 2007) n opera- tonal centers. Although some ssues were dentfied by PDt–5 (Marks and shay, 1998), many questons and problems reman unresolved. other new ssues have emerged snce then. Major landfallng hurrcanes between 2004 and 2008, such as Katrna, Rta, and Ike, revealed many crtcal needs not only for mproved weather forecasts but, more mportantly, for forecasts of storm mpact drectly related to socetal responses to these events. these are hghlghted n four recent na- tonal reports callng for acton to substantally mprove hurrcane forecasts (AGU, 2006; nsAB, 2006; nsB, 2007; oFcM, 2007); they partcularly cte 1 In ths context, user groups nclude both end users and ntermedate users who typcally are commercal weather provders and so-called value-added resellers.

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94 94 WHen WeAtHeR MAtteRs the rapd ntensty changes of hurrcanes threatenng the Unted states as a major challenge. Recent advances n scence and technology, especally n hgh-resoluton coupled modelng, ensemble model forecastng, hgh- performance computng, and socal behavoral studes related to hazardous weather events, have presented a great opportunty to develop a strategy and acton plan for an ntegrated forecast-and-response system that wll support rsk assessment, emergency management, and decson makng. Tornadoes and Severe Thunderstorms there has been consderable mprovement n understandng, predctng, and warnng for these hazardous phenomena as a consequence of success- ful research programs, deployment of a natonal network of Doppler radars, and other natonal Weather servce (nWs) modernzaton actvtes n the 1990s. Lead tme for tornado warnngs has ncreased from about 6 mnutes n 1993 to about 13 mnutes n 2008. However, questons stll reman concernng why only a small fracton of supercell thunderstorms produce tornadoes whle most do not. As a consequence, the false alarm rate for tor- nado warnngs s hgh, at 75 percent n 2008, whch s vrtually unchanged from 1993 when t was 73 percent. Research programs such as VoRteX2 need to contnue to address that queston, reduce false alarm rates, better understand tornado geness and dsspaton processes, deduce how and why some tornadoes become strong and volent whle others do not, and explore other unknowns about tornadoes and severe thunderstorms. Radars n the natonal operatonal neXRAD (or WsR-88D) network are spaced too far apart to detect the low-level portons of most supercells, whch s crtcal to detecton of tornadoes. Research needs to contnue the development of low-cost, adaptve scan- nng radars as a means to fill these gaps (e.g., Brotzge et al., 2006) both to reduce false alarm rates and mprove detecton of tornadoes now mssed. Recent studes by the nRc (e.g., 2002, 2008a) recommend addtonal upgrades to the natonal radar network. to dramatcally mprove tornado warnng lead tme wll lkely requre a shft away from warnngs based on detecton to warnngs based on forecasts. Much needed research s ongong toward the development of a warn-on-forecast system (e.g., stensrud et al., 2009), whch wll nvolve many of the mprovements n numercal model- ng and probablstc forecasts recommended here and elsewhere n ths report. there s also a contnung need for mproved understandng of the four-dmensonal structure of tornadoes, wth practcal applcatons such as mproved buldng constructon standards.

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 95 Flash Floods In many ways, flash floods are among the most dfficult phenom- ena to predct (see the dscussons n chapter 3). Many ssues related to quanttatve precptaton forecastng and hydrologc and flood predcton have been dscussed prevously by UsWRP PDt–8 (Frtsch et al., 1998) and UsWRP PDt–9 (Droegemeer et al., 2000). there s lttle skll n predctng the exact locaton of an upcomng flash flood untl the ran s well under way. even then, the area of heavest ranfall tends to be small and not al- ways well observed. Improvements n precptaton estmaton through use of multparameter radars wll help wth ths problem; the neXRAD agency partners (Department of commerce, Department of Defense [DoD], and the Department of transportaton [Dot]) have ntated a program to pro- vde dual-polarzaton capablty on all 166 WsR-88D radars wth comple- ton targeted for early 2013.2 Improvements n satellte-based precptaton estmaton and n cloud-to-ground lghtnng detecton (a useful surrogate for convectve precptaton) can help n remote, mountanous areas not well sampled by radar. Flash floods are an excellent example of VHI weather that can reap the benefits of a new mpacts forecastng paradgm by utlzng numercal model forecasts and observatons n a coupled hydrology–land–atmosphere model for flood mpacts forecastng. the need for a coupled dstrbuted hydrologc modelng framework s dscussed at length n chapter 3. A recent flash flood n the Atlanta, Georga metro area llustrates the challengng nature of flash floods. on september 20–21, 2009, more than 15 nches of ran n less than 24 hours (wth a maxmum of more than 21 nches n 38 hours) fell n a narrow corrdor generally less than a county wde. Although a broad area of the southeast was under a flash flood watch owng to the presence of an unusually most ar mass, there was no obvous way to predct the exact locaton or magntude of the event, even n hndsght. Whle a mesoscale boundary was orented generally west–east through the area, a band of thunderstorms set up and moved roughly perpendcular to the boundary. However, all of ths was unresolved by the operatonal regonal models, and forcng for the locaton of formaton of the ntal storm was not obvous ether from observed data or numercal model gudance. It remans to be determned whether a network of enhanced observatons provdng nputs to mproved data assmlaton technques and cloud-resolvng regonal models can mprove forecasts of heavy mesoscale precptaton. ths ssue 2 see http://www.roc.noaa.gv/wsr88d/DualPol/DualPolovervew.aspx.

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96 96 WHen WeAtHeR MAtteRs s further addressed n the Mesoscale observatonal needs and QPe/QPF sectons of chapter 3. Wildfires Wldfires are another opportunty to apply a new paradgm for mpacts forecastng. temperature, humdty, and dry lghtnng can play a role n wldfire ntaton, development, and spread, whle wnds and terran typ- cally play key roles n spreadng major wldfires. the wldfires themselves often develop ther own weather, becomng firestorms. there s a need for contnued mprovements n satellte sensng, ncludng fuel avalablty and the detecton and montorng of fires and ther ntenstes. Fre models can be coupled wth atmospherc and land-use models to generate mpact forecasts of threatened areas (e.g., clark et al., 2004). numercal model mprovements are crucal, ncludng terran and urban effects. A predcton system of ths type has been proposed (e.g., Bradley et al., 1999). Surface and Air Transportation Accordng to a recent nRc (2004) study, weather sgnficantly affects the safety and capacty of the naton’s roadways. Adverse weather s as- socated wth over 1.5 mllon vehcular accdents each year, accountng for approxmately 800,000 njures and 7,400 fataltes (FHA, 2009). Poor road or vsblty condtons often cause drvers to slow down, thereby sub- stantally reducng roadway capacty, ncreasng travel tmes, and n some cases contrbutng to chan-reacton accdents. It s estmated that drvers endure over 500 mllon hours of delay annually on the naton’s hghways and prncpal arteral roads because of fog, snow, and ce. ths conserva- tve estmate does not account for consderable delay due to ran and wet pavement. An mproved strategy for addressng the mpacts of weather on surface transportaton has the potental to help mtgate roadway congeston and save lves. Hgh-qualty weather observatons and forecasts specfic to the roadway envronment could help users make better decsons, thereby ncreasng travel efficency and safety durng adverse weather condtons. Improved road weather nformaton could also help those who construct, op- erate, and mantan the roadways to better respond to weather problems. Weather also s a major factor n causng delays (about 65 to 70 per- cent of the total occurrence) and economc losses to commercal avaton. Accordng to the Jont economc commttee of congress (U.s. congress, 2008), ar traffic delays n 2007 cost arlnes $19 bllon n ncreased operat-

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 97 ng costs and the Unted states economy $41 bllon. As the volume of ar transportaton ncreases, the demand for even greater efficency wll requre mproved qualty and use of weather nformaton. nextGen3 s a mult- agency (Dot, DoD, Federal Avaton Admnstraton, natonal Aeronautcs and space Admnstraton [nAsA], and Whte House office of scence and technology Polcy) ntatve to dramatcally mprove the management of ar transportaton by 2025. Weather nformaton plays an mportant role n nextGen, enablng the dentficaton of where and when arcraft can and cannot fly. In buldng nextGen, weather nformaton s beng desgned to ntegrate wth, and support, decson-orented automaton capabltes and human decson-makng processes. Weather nformaton supports trajectory- based plannng and decson makng. the nextGen weather and automaton capabltes wll support catalogng and analyzng flght plans and provde recommended routes to plots and dspatchers. Weather nformaton n the form of meteorologcal varables that are observed or forecasted (e.g., storm ntensty, echo tops) need to be translated nto nformaton that s drectly relevant to nextGen users and servce provders, such as the lkelhood of a flght devaton, arspace permeablty, and capacty. Uncertanty n meteo- rologcal phenomena that have sgnficant mpact on ar system capacty s beng managed through the use of probablstc forecasts that wll nclude the three-dmensonal locaton, tmng, ntensty, and the probablty of all possble outcomes. Persistent Hazardous Conditions these VHI weather phenomena generally occur as a result of prolonged anomalous weather condtons lastng days, weeks, or even years. Impacts can result from ether excess or deficent precptaton, anomalously warm or cold temperatures, and often n combnaton wth anomales of wnd and sunshne. River Floods Although sometmes generated by a sngle ranfall event, the worst floods are often a combnaton of prolonged ran and snowmelt, and oc- cur over a longer tmescale than flash floods, such as the Mdwest floods of 1993, whch are thought to be the largest and most sgnficant recorded 3 see http://www.jpdo.gov/ndex.asp.

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98 98 WHen WeAtHeR MAtteRs flood n the Unted states. Floodng occurred across nne states, resultng n 48 deaths and approxmately $21 bllon n damages (ncDc, 2010). Improvements n the ablty to predct anomalously wet patterns could have an mpact on the ablty to antcpate rver floods and allow emergency and water managers to plan ahead. Drought Drought has huge mplcatons for agrculture, water supply, recreatonal ndustres, and varous commercal enterprses. shfts n populaton to low- precptaton areas where water s normally n short supply—and to urban areas where supples may be lmted—have already brought water supply problems, water restrctons, and dsputes to many places n the Unted states. A recent workshop has summarzed some of the ssues and re- search needs facng predcton of drought on seasonal to decadal tmescales (schubert et al., 2007). Research needs range from a greater understand- ng of the forcng factors (oceanc, el nño–southern oscllaton [enso], aerosol feedback, vegetaton, and others), especally wth respect to varous clmate change scenaros, to mproved numercal modelng of the coupled land–ocean–atmosphere system. Heat and Cold Waves each of these, typcally lastng up to a few days, can have serous m- plcatons for human health, agrculture, and other ndustres. Hundreds to thousands of fataltes (cDc, 2006) result annually from heat waves n the Unted states alone, ncludng about 700 excess deaths durng the 1995 heat wave n chcago alone. there s also a strong correlaton between heat waves and pollutant levels, and the synergstc effects of heat and poor ar qualty lead to elevated morbdty levels. Because heat waves wth the largest mpacts last for many days, there s a pressng need to mprove medum- to extended- range forecastng. temperature anomales have huge economc mplcatons for energy use and for commercal utlty provders. For example, urban electrcty usage ncreases 3 to 5 percent for each 1°c ncrease n ambent ar temperature above about 22°c (salor and Detsch, 2007). Air Quality Ar qualty and ts mpacts on health and the economy nvolve far more than just the pollutants emtted nto the atmosphere. Weather factors such

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 99 as nversons, wnd speed and stablty, precptaton, and other factors are often controllng nfluences. Ar stagnaton epsodes often nvolve a pattern of strong, low-level nverson and lght wnds that perssts for a few days. one study (schwartz and Dockery, 1992) ndcated that 60,000 people de n the Unted states each year because of poor ar qualty. Improvements in Impacts Forecasting the mpacts of VHI weather epsodes tend to be maxmzed n urbanzed areas where large numbers of ctzens and nfrastructure are concentrated. even for the smallest of the VHI weather phenomena (e.g., tornadoes and flash floods) sgnficant portons of an urbanzed area can be serously m- pacted. Further ssues specfic to the urban envronment are addressed n followng sectons. Research that leads to mproved understandng, montorng, predcton, and communcaton of VHI weather phenomena wll result n fewer njures and fataltes and reduce the mpacts of the tens of major natural dsasters that annually mpact the Unted states. In addton to the economc mpacts of VHI weather already descrbed, there are countless applcatons n whch mproved weather nformaton can result n enhanced cost-effectveness and savngs for publc enttes, busness, and ndustry. socal scentsts and economsts are needed to help quantfy the benefits of weather data and forecasts to these applcatons and to define key mpact parameters (as ds- tnct from tradtonal weather parameters). Impacts of Climate Change on Very High Impact Weather A major challenge s to understand the effects of clmate change on VHI weather and ts potental long-term socoeconomc mplcatons. Potental changes n storm tracks and ntensty, and the frequency of severe drought and floodng events are of great value n rsk assessment, adaptaton, and mtgaton. Although recent studes have suggested that the ntensty and perhaps even the number of extreme weather events may ncrease (e.g., Anthes et al., 2006; Knutson et al., 2010; trapp et al., 2007; trenberth et al., 2003), t s dfficult to evaluate and valdate the results because of the lack of observatons and lmtatons n clmate models to represent “weather.” the relatvely low resoluton and nsufficent physcal representaton n the current clmate models have led to great uncertanty n the assessment of the mpact of clmate change on VHI weather. A well-desgned systematc approach s urgently needed to mprove clmate model physcal param-

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124 124 WHen WeAtHeR MAtteRs exposed to varable stresses throughout a sgnficant fracton of the lowest regon of the atmospherc planetary boundary layer (PBL) where wnd shear and turbulence are typcally most severe. At nght when the PBL can be very shallow (50 to 100 m), the lower part of the blades can be exposed to stable condtons wth lttle mechancal turbulence but strong vertcal wnd shear n both speed and drecton. At the same tme, the upper reaches of the blades can rotate through (and above) the cappng PBL nverson where shear and turbulence can both be sgnficant. the nonhomogeneous nature of the envronment n whch the turbne operates can place sgnficant mechancal stresses on the turbne blades and gearbox. In addton to the natural stresses from ambent condtons, the wnd turbnes are exposed to wake turbulence created by neghborng turbnes wthn the wnd park. these condtons place demands on the desgn of the wnd turbne that, n turn, requres detaled knowledge of the mean and turbulent flow condtons throughout the wnd park that can only be acheved through a combnaton of representatve local observatons and numercal modelng. obtanng relable summary data on the role of weather (wnd, turbu- lence, cng, temperature, and lghtnng) on the falure of wnd turbnes n general and specfic subassembles s dfficult. often the cause of the falure s not known or s not released for propretary reasons. But there are some studes that summarze the falure rates (wthout causal attrbuton) for wnd turbne systems and ther varous subassembles. tavner et al. (2008) provde a valuable overvew of the relablty of wnd turbne systems based on an analyss of more than 6,000 wnd turbnes n Denmark and Germany that have been n operaton for 11 years. they found falure rates for varous subassembles of 1 MW turbnes ranged from about 0.05 to 0.5 falures per turbne subassembly per year. the hgher rates occurred wth the electrcal systems and the rotors (blades and hub) whle gearboxes had the lowest falure rate. they also found falure rates ncreased wth turbne sze, but that falure rates had decreased over tme (Fgure 4.4). Wind Plant Architecture It has long been known that the longtudnal and lateral spacng of n- dvdual wnd turbnes strongly nfluences the power generatng efficency of the wnd farm. If the wnd turbnes are placed too close together, there wll be a reducton n the output of all downwnd turbnes due to the wake velocty deficts of the upwnd turbnes. Placng the turbnes too far apart reduces the number of turbnes n the wnd farm and thus reduces the amount of energy that can be generated per unt area of the wnd farm.

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 125 FIGURE 4.4 Wind turbine failure rates (failures per turbine per year), based on an analysis of over 10,000 wind turbines in operation over 15 years. Most of the data come from turbines in Denmark and Germany, although an early data point (1987) comes from the Electric Power Research Institute (EPRI) in the United States. Compared to the 1987 EPRI datum, there has been an order of magnitude improvement in failure rates through 2004. However, the improvement since 1993 is less. Also shown are comparable failure rates for steam turbine generators, which have lower failure rates (around 0.2), combined-cycle gas turbines that have comparable failure rates (~1), and diesel generators that have higher failure rates (~2). SOURCE: Tavner et al. (2007). Both of these effects negatvely nfluence the cost and efficency of the wnd farm and the power t can generate. Recent studes (e.g., Werle, 2008) have demonstrated that even wth the relatvely large longtudnal and lateral separaton dstances of seven turbne-blade dameters, downwnd turbnes wll sometmes delver only about 65 percent of the power generated by the upwnd turbne. therefore, optmzng the layout of the turbnes n a wnd farm s crtcal. the problem of wnd farm configuraton s further complcated by the effects of local topography. often the areas wth the hghest wnd potental are those offshore as well as onshore locatons wth terran relef. Both types of stes can present specal aerodynamc challenges to the layout of the wnd farm. offshore stes are typcally mpacted by sea breeze crculatons,

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126 126 WHen WeAtHeR MAtteRs tme-varable surface frcton effects, and stable condtons through the lower boundary layer. Wnd farms n areas of terran relef are subject to locally gener- ated mechancal turbulence. In both cases, t s mportant to also consder the spatal varablty of wnd and turbulence across the wnd park. such knowl- edge cannot be ganed from ambent wnd observatons alone, and advanced computatonal flud dynamcs (cFD) and large-eddy smulaton models are needed to locate the wnd turbnes wthn the wnd farm n order to mnmze wake effects from adjacent wnd turbnes. Models are also nstrumental n optmzng the locatons of meteorologcal observng stes, whch n turn can provde data assmlated by the models. Operations the effectve operaton of a wnd park requres wnd forecast nforma- ton on dfferent tmescales and across the spatal doman of the wnd park (many of whch span hundreds of square klometers of spatally varyng topography). Forecasts on the 0- to 48-hour tmescale are mportant for determnng the amount of wnd energy that can be provded by the wnd park, and also determnng how much energy wll need to be purchased from conventonal fossl energy sources. As wnd parks become larger or are aggregated onto the electrc grd, ther senstvty to wnd varatons and to wnd-forecast accuracy s lessened to a degree. on the other hand, wnd park operatons are very susceptble to so- called wnd ramp events, whch are abrupt, major changes n wnd speed over a relatvely short perod of tme (one smple, quanttatve definton refers to a wnd power change ≥50 percent over an nterval of ≤4 hours). the problem of “wnd ntegraton” s a sgnficant operatonal obstacle fac- ng wnd energy producton. the term refers to the measures energy system operators must take when wnds change rapdly (wnd ramp events), causng a sudden ncrease or decrease n wnd power generated by turbnes. electrc utlty companes usually have a specfic generaton configuraton consstng of a mx of coal, ol, gas, hydro, wnd, and nuclear power. When wnds pck up, the amount of power generated by the wnd turbnes ncreases rapdly, causng excess power to be njected nto the generaton system. Because the system s not capable of handlng endless amounts of power, the utlty company must quckly ramp down generaton from the wnd turbnes (some wnd turbnes are able to have ther rotatonal speed controlled) or ramp down other, conventonal sources and route excess electrcty to neghbor- ng utltes. In the case when the wnds may abruptly decrease, the result s a sudden need to mport power and turn gas turbnes on quckly, often

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 127 n mnutes. to mtgate the potental for a ramp-up requrement, operatng utltes often keep a spnnng reserve of gas turbne generators runnng ready to fill the power gap. ths, however, s not an deal soluton because the spnnng reserve ncreases the cost of wnd power and can decrease potental carbon savngs. there are also costs assocated wth slowly cyclng wnds when conventonal thermal (coal) unts are ramped up and down; n these cases, there are excessve wear-and-tear costs on the thermal unts than can be apprecable. Wnd ntegraton costs are dfficult to estmate and are not smply the dfferental between operatons wth and wthout wnd-generated power (Mllgan and Krby, 2008). In ther analyss, they present the example of a system that has sufficent capacty to meet a fast ramp, but n order to meet the ramp, a peakng unt must be utlzed. In ths case, the baseload unt has an energy prce of $10/MWh, but s unable to ncrease output quckly enough to meet the ramp. A peakng unt s brought onlne at a prce of $90/MWh to meet the ramp. If the margnal unt sets the energy prce n a market, the energy prce rses durng the rampng perod because the onlne base unt s not flexble enough. Had the ramp been sustaned durng a lon- ger perod of tme, the base unt could have met the ramp requrement, and the energy prce would have remaned at $10/MWh. ths example ponts out that rampng can be extracted (at a hgh prce) from the energy market. Further, n a system wth sgnficant wnd penetraton, the ramp scenaro can be exacerbated, necesstatng even more rampng capablty at an even hgher prce. Mllgan and Krby (2008) further argue that “poolng loads and resources nto a larger balancng area holds the promse of allowng addtonal wnd to be ntegrated nto the system at lower cost.” to help mtgate the wnd ramp/ntegraton problem, there s a pressng need to develop very short-range nWP and nowcastng methods that can relably predct wnd ramp events on the 30-mnute to 6-hour tme frame. Provdng accurate and relable, cost-effectve forecasts (wth equvalently low false alarm rates) of the onset, duraton, and magntude of wnd ramp events that are specfic to the locaton of wnd farms may be the sngle most pressng contemporary meteorologcal need n support of wnd power operatons. Need for Improved Meteorological Observations Meteorologcal observatons—prmarly wnd and turbulence, but also temperature—are requred to ad n wnd park assessment, stng, and desgn and to assess the performance of ndvdual wnd turbnes. they are also

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128 128 WHen WeAtHeR MAtteRs needed to ntalze nWP models and for data assmlaton models that en- hance model performance. they are also requred to assess (valdate) model performance under dfferent meteorologcal and topographc regmes. Me- teorologcal observatons are also necessary for very short-range predcton (.e., nowcastng) of wnd changes on the 0- to 2-hour tmescale. Because of the sgnficant vertcal extent of large wnd turbnes and the effects of wnd shear and turbulence, t s essental to have detaled knowledge of the mean and turbulent structure of the PBL (and beyond, n some cases), up to heghts of about 0.5 km above the land or water surface. Vertcal profiles need to be hghly resolved both n space (5- to 10-m heght resoluton) and tme (on the order of 5 mnutes). In some cases, research and development s needed to develop mea- surement systems that better meet the needs of the wnd energy ndustry. In partcular, remote sensng wnd profilers—optcal or ultrahgh frequency (UHF)—are needed to provde long-term and hgh-resoluton profiles of vector veloctes up to 300 to 500 m. they need to be cost-effectve as well: affordable, easy to nstall and mantan, and sufficently robust to operate unattended for years. the current state of mesoscale observatons s nadequate to support the hgh-resoluton modelng needs of the wnd energy ndustry to predct wnd energy at, and wthn, wnd parks. ths wll requre dense arrays of surface observatons (both wnd and state varables) both for nowcast- ng and moderately dense arrays for mesoscale nWP modelng, but also remote sensng profilers to adequately characterze wnd and turbulence through the PBL. the ablty to specfy the detals of the desgn of these networks s nadequate, and that also s a research area requrng hgh prorty. the mesoscale observng ssues and needs dscussed n chapter 3 would well serve the needs of the wnd energy enterprse. there t was recommended that humdty, wnd, and durnal boundary-layer structure profiles are the hghest prorty for a natonal mesoscale network, the stes for whch need to have a characterstc spacng of approxmately 150 km but could vary between 50 and 200 km based on regonal consder- atons. Because the most mportant tmescales for mtgatng ramp events s short—less than 1 hour—t can be estmated from taylor’s hypothess that nowcastng a ramp event wth a 15 m s−1 wnd speed requres wnd observatons about 55 km upstream, whch s consstent wth the prevous recommendaton. the recommended profiler network would, of course, also be nvaluable for producng mproved nWP predctons of many wnd ramp events on longer tmescales.

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 129 Need for Improved Modeling A herarchy of models, each smulatng a range of spatal scales, s re- qured to address the varous wnd-dependent aspects of wnd turbne/park desgn and operaton, ncludng the followng: • cFD models are needed to specfy turbulence features at, and down- wnd of, ndvdual turbnes and assess the flow nteractons among adjacent turbnes. • Hgh-resoluton atmospherc (ncludng large eddy smulaton) mod- els are needed for the purpose of descrbng the turbulent flow characterstcs and structure of the ambent PBL and nteractons wth turbulent wakes from ndvdual wnd turbnes and large arrays of turbnes. • Hgh-resoluton mesoscale models (grd resoluton of 0.5 to 1.0 km) are requred to assess the wnd energy potental (for prospectng applca- tons) of regons up to 103 km n scale. they are also needed to forecast the wnd energy that can be provded by a gven wnd park—ncludng varatons wthn the park—over forecast perods of 48 to 72 hours. For the latter purpose, ensemble predctons wll ad n determnng the range of wnd power output that can be antcpated, whch s useful for assessng the need for alternatve power sources. nowcastng algorthms are needed to provde relable predctons of very short-range changes n the wnd field up to 2 hours. Need for Improved Collaborations In spte of the commonaltes and feedbacks among research challenges n the four key areas—turbne dynamcs, stng and array effects, mesoscale processes, and effects of a changng clmate—research n any one area has largely been conducted ndependent of the research challenges of the other three areas. enhanced nterdscplnary collaboratons among researchers can provde results that are more benefical, more effectve, and tmeler. In ths way, for example, optmum wnd turbne arrays can be desgned as a consequence of closer collaboraton of flud dynamcsts and mesoscale meteorologsts, and mproved long-range wnd resource plannng may re- sult from ncreased nteractons among not only mesoscale and clmate researchers but also socoeconomsts. In the same way, closer nteractons are requred among observatonalsts, expermentalsts, modelers, and users. effort now focused wthn ndvdual dscplnes needs to be augmented by

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130 130 WHen WeAtHeR MAtteRs a flatter, more nterdscplnary approach. ths apples both to ndvdual researchers and groups as well as to the governmental agences that support and prortze the research. Partnershps are essental n developng the modelng tools needed to desgn and operate wnd parks. there are mportant complementary roles to be played by the publc, prvate, and academc sectors, and the three sectors need to find effectve ways to collaborate. Solar Energy Background solar power refers to the producton of electrcty, drectly or ndrectly, from ambent sunlght. Photovoltac (PV) systems convert sunlght drectly nto electrcty usng arrays of solar cells of varous types, such as thn-film, monocrystallne slcon, polycrystallne slcon, and amorphous cells. Arrays of PV panels can provde electrcty drectly to ther hosts (e.g., homes, facto- res, office buldngs, arports) or they can be configured n very large arrays to comprse photovoltac power statons that provde electrcty to the power grd. the olmedlla Photovoltac Park n span s currently the world’s largest PV plant.18 Bult n 2008, the plant has more than 160,000 solar PV panels to generate peak power of 60 MW, whch s enough electrcty to supply more than 40,000 homes. concentrated solar power systems produce electrcty ndrectly by usng combnatons of mrrors, lenses, and solar trackers to focus sunlght from a large area onto a small area where the concentrated solar energy s used to heat water for use n a conventonal thermal power plant. the solar energy Generatng systems faclty n the Mojave Desert s reported to be the largest solar system n the world, consstng of nne solar power plants that have a combned capacty of 354 MW.19 Yet, solar energy today only supples about 0.9 percent of the U.s. domestc energy producton from all renewable sources (eIA, 2008b; Fgure 4.3a). The Problem the avalablty of electrcty from solar energy systems, lke that from wnd farms, s hghly varable n space and tme, whch poses sgnficant challenges for a power grd that requres stablty and predctablty. Devel- opers of large solar plants and utltes that utlze dstrbuted PV systems that 18 see http://www.pvresources.com/en/top50pv.php. 19 see http://solar.calfinder.com/blog/news/worlds-largest-solar-plant-segs/.

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 131 encompass resdental and commercal nstallatons have common needs for relable observatons, hstorcal and real-tme databases, and accurate forecasts on a varety of scales. exstng hstorcal, natonal solar radaton databases are avalable from the Doe natonal Renewable energy Laboratory (nReL, 1995, 2007), the state Unversty of new York at Albany (Perez et al., 2007), and nAsA.20 they are based on n stu measurements from a few tens of surface-based radometers together wth satellte cloud magery and analytcal nterpola- ton algorthms. However, the accuracy of hourly estmates of surface solar rradance from satellte magery s only ±20 percent. Addtonally, the temporal resoluton of 1 hour does not meet user needs for 15-mnute data (some users may requre temporal resoluton as fine as 1 mnute); nor s the spatal resoluton (≥10 km) of these databases consstent wth many user needs for data resoluton of 1 km. It s notable, however, that an excellent mesoscale solar and meteorologcal measurement network and database exsts at the southern Great Plans ste of the Doe Atmospherc Radaton Measurement program (Ackerman and stokes, 2003), whch can provde an nvaluable resource for testng and evaluatng alternatve measurement, analyss, and forecastng methods. Utlty operators requre solar resource forecastng on several tmescales: ≤3 hours for dspatchng to enable a steady power supply to the grd; 24 to 72 hours for system operatons plannng; and seasonal to nterannual forecastng for economc analyses and system plannng. However, today there does not exst an operatonal solar nsolaton forecastng capablty that meets user needs. Needs the needs of users and the shortcomngs of exstng measurement net- works, solar databases, and forecast models were addressed n a recent AMs communty workshop (Weatherhead and eckman, 2010) and a recent nReL workshop and subsequent extensve needs study (Renné et al., 2008); these findngs reflect ther conclusons: • there s a pressng need for hgh-resoluton (15 mnutes or less) solar resource data derved from the hourly model results, and/or from add- tonal hgh-qualty measurements. ths nvolves obtanng more relable ste- specfic data from extrapolaton methods, more spatally refined satellte- 20 see http://eosweb.larc.nasa.gov/sse/.

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132 132 WHen WeAtHeR MAtteRs derved solar resource estmates, and on-ste measurements of downwellng solar radaton (all components) and downwellng nfrared radaton. • Relable, operatonal solar forecastng s not avalable today. Users need 12- to 72-hour solar resource forecasts, as well as very short term (≤3 hours) and seasonal-to-nterannual forecasts, for use by system operators n system plannng and load-followng operatons. • An nteractve archve of solar resource nformaton s needed so that developers, utltes, system operators, and system planners can access solar resource nformaton needed for specfic analyses and applcatons. • Lower-cost solar resource measurements and assessments are needed for key locatons (e.g., dstrbuted PV systems). • Improved satellte datasets are requred that encompass mproved estmates of aerosols, better detecton of snow cover, and hgher spatal resoluton. Relationship to Other Weather Research Needs Improved observatons, smulatons, and predctons of wnd and tur- bulence and solar radaton are needed wth hgh spatal and temporal resoluton and accuracy to optmally locate, desgn, and operate wnd and solar energy facltes. these efforts wll requre a focused, hgh-prorty natonal research and R2o program that would be carefully and closely ntegrated wth the observng and predctng ntatves and socoeconomc actons recommended n chapters 2 and 3 of ths report. In ths way, pre- vous recommendatons pertanng to mproved nWP wth global nonhy- drostatc models (page 58), mproved quanttatve precptaton estmaton and forecastng (page 69), mproved hydrologc predcton (page 70), and mproved mesoscale observng systems (page 87) wll all postvely mpact the nformaton needs of the renewable energy enterprse as they pertan to electrcty generaton from wnd and solar (but also from hydro resources). By the very nature of these applcatons, the efforts recommended here need to be a true publc–prvate partnershp wth sgnficant nvolvement of academa as well. to be successful, these efforts wll requre the formaton of effectve collaboratons and partnershps among power system desgn- ers, operators, grd managers, observatonalstsresearchers, forecasters, and modelers. It s encouragng that the Doe has nteracted closely wth aca- dema and the prvate sector, as exemplfied by the communty workshops the Doe has organzed to facltate mproved weather-related support for wnd and solar energy producton. And noAA has recently ndcated that ts next Generaton strategc Plan (scheduled for release n summer 2010)

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eMeRGInG WeAtHeR ReseARcH AnD tRAnsItIonAL neeDs 133 wll explctly nclude a focus on support for energy producton from renew- able resources.21 Recommendation: The effective design and operation of wind and solar renewable energy production facilities require the development, evalu- ation, and implementation of improved and new atmospheric observ- ing and modeling capabilities, and the decision support systems they enable. The federal agencies should prioritize and enhance their devel- opment and support of the relevant observing and modeling methods, and facilitate their transfer to the private sector for implementation. 21 see http://www.pp.noaa.gov/ngsp.html.

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