THE NSF/NCAR GULFSTREAM GV:A NEW PLATFORM FOR STUDIES OF CLOUDS

William A. Cooper, Jeffrey L. Stith, David C. Rogers, and Jorgen B. JensenNational Center for Atmospheric Research, Boulder CO USA

1. AIRCRAFT CHARACTERISTICS

A new research aircraft, operated by the Na­tional   Center   for   Atmospheric   Research   forthe   National   Science   Foundation,   is   now   inoperation (Fig. 1): 

Figure   1:   The   NSF/NCAR   GV   ResearchAircraft (HIAPER) at takeoff.

The   aircraft,   also   called   “HIAPER”   (HighAltitude   Instrumented   Airborne   Platform   forEnvironmental Research), is capable of flightto   15.5   km   MSL   (51,000   ft),   and   its   range(typically   around   8000   km   or   5000   n   mi)makes   studies   possible   that   have   globalscale. The aircraft was selected for its abilityto   support   research   in   climate   science,atmospheric   chemistry,   weather   andmesoscale studies, global atmospheric cycles,aerosols,   clouds,   and   many   other   areas   ofgeoscience.   It  provides  special  opportunities

for   research   in   the   upper   troposphere   andlower stratosphere and for studies that exploitits   range   to   achieve   coverage   up   to   globalscales.

 

Figure   2:   Modifications   to   be   able   to   carryinstrument canisters under the wings.

Figure   3:   Illustration   of   some   of   the   mechanical   modifications   made   to   the   aircraft   toaccommodate research equipment. In addition, extensive installation of cables and other wireprovides   for   research   power   distribution   to   instrument   locations,   signal   routing,   and   dataacquisition and monitoring.

The aircraft has been modified extensively toaccommodate   research   equipment,   asillustrated   by   Figs.   2   and   3.   Thesemodifications   included   the   installation   ofaperture   pads   (e.g.,   for   inlets),  instrumentaperture   plates,  optical   view ports,   fuselagemounts,   and   four   forward   fuselage   pads.Cabin pressurization (to a pressure altitude of6000 ft when flying up to its ceiling) provides acomfortable   working   environment   forinstrument   operators   and   other   crewmembers. The payload with maximum fuel is3400   lb;   maximum   payload   is   8300   lb,   buttypical  payloads  are  about  4000   lb  and  are

often   limited   by   the   available   floor   space.Substantial   power   is   available   for   researchinstrumentation, up to 20 KVA of 115VAC ateither 60 or 400 Hz (or split between these).The   platform   is   certified   for   flight   as   astandard­category   aircraft,   and   instrumenta­tion   provided   also   meets   these   certificationstandards (as must all equipment provided byusers).

The aircraft was delivered in 2005 and beganflights in support of research in 2006, althoughinfrastructure   upgrades   have   continued   andare still  continuing (e.g.,  the addition of wingstores).   The  acquisition  and performance   of

the  aircraft   are  described  by  Laursen  et  al.(2006),   and   the   Investigator's   Handbookprovides   additional   detail;   the   latter   andadditional  documents  are  available   from  theNCAR   Research   Aviation   Facility   web   site:www.eol.ucar.edu/instrumentation/aircraft/G­V. 2. INSTRUMENTATION

Standard   instrumentation:  For   normal   mis­sions, there are likely to be three categories ofinstrumentation   in   use,   standard,   special­request, and user­provided. The first  is stan­dard for the aircraft and normally operated onall  flights; this set  includes measurements ofposition (duplicate Honeywell LASEREF IV in­ertial   systems,   Honeywell   12­channel   globalpositioning systems (GPS), and when useful aGPS system with differential capability), stateparameters (pressure, temperature, and dew­point), and wind (using a gust system sensingpressure   differences   among   ports   placed   inthe forward radome). There are also a set ofstandard   inlets   to   provide   air   samples   tocabin­mounted instruments, and a camera forvideo  recording  is mounted under a wing  toprovide   a   good   view.   Most   experiments   willalso   use   some   of   the   available   aerosol   in­struments and/or hydrometeor spectrometers,including   a   cabin­mounted   CN   counter   andmobility   analyzer   and   wing­mounted   sizespectrometers   for   aerosols,   cloud   droplets,and ice crystals. The spectrometers have fastelectronics   to  permit  measurements  at   flightspeeds   up   to   about   235   m/s,   a   speedcommon   during   high­altitude   flight   of   thisaircraft.  A   tunable­diode  laser  hygrometer   isavailable   for   measuring   humidity   at   uppertroposphere   /   lower   stratosphere   values.

These capabilities are all available on requestand   the   instruments   are   operated   andmaintained by NCAR.

Table 1, appended to the end of this paper,summarizes   the   available   standardinstruments.  Some additional  instruments  foratmospheric  chemistry  are supported by  theAtmospheric Chemistry Division of NCAR andare also requestable.

Special­request instruments. An extensive setof special instruments have been or are beingdeveloped for use on the GV. (See Table 2 atthe end of this paper.) These instruments aredesigned  specifically   to  operate  on   the  GV,and so will meet certification requirements forexpected  deployments.   For   some,  operationof   the   instrument   is   best   conducted   byarrangement   and   involvement   of   thedevelopers,  although  some  will   be  operatedby NCAR for the community. 

Of special interest to the cloud­physics com­munity  will  be  the  instruments  for  character­izing   hydrometeors.   A   wing­mounted   SmallIce Detector (SID­2) has been developed foruse on the aircraft, and a new probe called a3V­CPI is under development by SPEC Corp.;the  latter  combines  two orthogonal  2D­arrayspectrometers (as in the SPEC 2D­Stereo in­strument) with a SPEC Cloud Particle Imager(CPI),  using the spectrometers to trigger theCPI. Also of special utility to studies of cloudswill  be  the cloud  radar   (initially  W­band,  butenvisioned to become dual W/K band), a highspectral resolution lidar (HSRL), and a radia­tion­sensing   package   consisting   of   spectralradiometers   as   well   as   measurements   of

spectrally  resolved   actinic   flux. An aerosolmass spectrometer will provide information onthe   composition   of   aerosol   particles,   and   acounterflow   virtual   impactor   is   available   formeasuring   total  water  content   in  clouds andfor   providing   residue   particles   fromevaporated cloud droplets  or  ice particles  toinstruments for analysis.

User­supplied instruments. Most payloads willalso   include   user­supplied   instruments   forspecial needs. There is ample power for mostsuch instrumentation, and there are capabili­ties  for   incorporating  the measurements   intothe recorded data files or for providing infor­mation   from   the   standard   data   system   tothese   instruments.   Some   special   require­ments are associated with certification of suchinstruments,   so   early   discussion   is   neededbefore such planned uses. 

3. SATELLITE COMMUNICATIONS

Early  operations  of   the   aircraft   have  shownthat  the satellite communications system en­ables   a   new   style   of   operation,   in   which   adistributed   team   of   investigators   canparticipate in the missions remotely while theaircraft   covers   continent­spanning  distances,perhaps   without   returning   to   the   originatingpoint   for   a   week   or   more.   The   systemprovides for telemetry of measurements to theground where they are made available via in­ternet to an extended observing team, someof whom can remain at their home institutionsand  still   participate   in  missions.   It   also  pro­vides   for   transmission   of   images   from   theground to the aircraft so that investigators onthe ground can construct images representing

developing weather situations or other eventspertaining to flight objectives and then trans­mit those to the crew on the aircraft. Commu­nications are via text messages (internet relaychat) that are logged so that they can be dealtwith   when   it   is   convenient   for   the  air   crew.Those   on   the   ground   can   see   themeasurements   as   they   are   made,   see   theimages from the video camera on the aircraft,and communicate  with   the  scientists  on   theaircraft.   Those   in   the   air   can   see   updatedsatellite or radar images sent from the ground,receive   updated   weather   information   and“nowcasts” and other model output during theflight,  and discuss  flight  procedures  with  theextended   team   on   the   ground.   It   maylaterprove   possible   and   advantageous   totransmit   measurements   from   the   aircraft   forincorporation or assimilation into models. Theplatform   is   also   attractive   to   consider   forexploiting  targeting of  observations,  becausetargets could be determined during flight andtransmitted   for   incorporation   into   the   flightplan.

These capabilities  were  exploited during  thePACDEX (Pacific Dust Experiment) campaignby   PIs   J.   Stith   and   V.   Ramanathan.   Someresults   from   that   experiment   are   includedelsewhere in this conference; cf., e.g., Stith etal.,   2008.   The   flight   crew   consisted   of   tenpeople   who   flew   from   Colorado   to   eitherAlaska or  Hawaii  and  then on  to  Japan  (cf.Fig.   4)   in   order   to   cover   large   parts  of   thePacific Ocean. To conduct repeated flights, aground­based   team   monitored   the   weatherand developed tentative flight plans that werecommunicated   to   the   flight  crew  during  andbetween   flights.   The  operations  center  re­

Figure 4: Sample flight track (15 May 2007),showing   a   flight   segment   from   AnchorageAlaska to Japan during PACDEX, with a lowlevel   flight   segment   (in   yellow)   enroute   tostudy dust emerging from Asia. 

mained   in   Colorado   even   for   the   flightsconducted   from   Japan.   Investigators   atlocations including the University of Iowa (G.Carmichael) were able to run chemical trans­port models while remaining at their home in­stitution, then communicate the results to theoperations  center   for   flight  planning  and   forforwarding to the air crew. 

Another   example   was   the   Terrain­InducedRotors  Experiment   (T­REX;  cf.  Grubišić  andDoyle, 2006), which was conducted by PI V.Grubišić and associates from a location in thelee   of   the   Sierra   Nevada   Mountains   ofCalifornia   while   the   GV   remained   based   inColorado. Ferry to or from Colorado requiredless than 2 h, leaving about 6 h for operationsin the study area. This allowed the instrumentoperators  to  remain  based in  Colorado  and

Figure 5: The flight track of the PACDEX flightof 5 May 2007 to study a cold front over thePacific Ocean. The flight began and ended inAnchorage Alaska; to set the scale, Hawaii isvisible at the bottom of the plot and Japan onthe  left  side. The yellow contour  is  the dustplume  predicted  by   the  STEM model   of  G.Carmichael (Univ. of Iowa) and collaboratorsfor   the  time of   the  flight,  with  a dust  plumeriding   along   a   jet   associated   with   the   coldfront.   This   image   was   transmitted   to   theaircraft  during  the flight  to help them designthe flight track, shown as the orange line.

yet   be   able   to   respond   quickly   when   theweather was appropriate for flight operations.The speed and range of the aircraft  make itpossible to conduct flights from a single baseand yet cover many flight objectives, perhapseven  those of  different  experiments (as wasdone   in   the   “Progressive  Science”   flights  of1996, when four different teams shared use ofthe   aircraft   in   order   to   meet   their   differentneeds, requiring flight sometimes to near the

Arctic Circle, sometimes to the Pacific Oceanoff   the   coast   of   Mexico,   and   sometimesacross the latitudinal span of the U.S., all froma   single   base   in   Colorado.)   The   START­08project   recently   conducted   a   flight   fromColorado to over the Hudson Bay and back ina single flight, as shown in Fig. 6. This rangeenables a different experimental model, usingthe   ability   of   the   aircraft   to   reach   distanceweather events and conduct experiments withmultiple objectives and weather targets.

It is likely that this continent­spanning style ofoperation will become common in future usesof the aircraft. The speed of the aircraft makesit  possible  to  collect measurements over dis­

Figure 6: Sample long­range flight (START­08flight 1, 18 April 2008, 7 h duration).

tances   that   span   regions   observed   bysatellites   or   modeled   by   global   models,opening   new   opportunities   for   validationstudies.   The   communications   link   alsoprovides opportunities for educational uses ofthe operations  that are only beginning  to bedeveloped.

4. SPECIAL   OPPORTUNITIES   FORSTUDIES OF CLOUDS

The capabilities of this aircraft and instrumen­tation provide new opportunities for studies ofclouds, many linked to the performance of theaircraft   but   others   also   associated   with   thenewly   developed   or   under­development   in­strumentation. These include:

l The ability   to  reach most  sub­tropicalCirrus clouds and to measure the sizedistributions,   ice­crystal  residues afterevaporation,   and   radiative   propertiesof such clouds;

l The   ability   to   climb   rapidly,   at   ratesmatching ascent rates of most Cumu­lus clouds, and so to observe the verti­cal   development   of   Cu   via   repeatedpenetration of rising parcels; cf. Fig. 7;

l The ability to cover distances appropri­ate for climate­scale studies, so that itis possible to characterize clouds overareas comparable to grid sizes in glob­al   models   or   to   reach   remote   mid­ocean locations in order to character­ize the clouds in ways that have clima­tological significance;

Figure  7:  Measured   rate  of  climb  (ROC)  vsaltitude   for   sample   climbs   of   the   GV   withnormal   payload.   Red   dots   show   an   initialclimb with full   fuel;  black dots show a climbmidway through an 8­h flight.

l High­speed   response   to   developingweather,   so   that   clouds   can   bereached   rapidly   during   their   earlystages of growth or practical researchareas   can   be   covered   to   targetparticular cloud or weather conditions;

l Mobility   upward   and   downward,   sothat   observers   on   the   aircraft   canbenefit   from   an   unobstructed   high­altitude   view   of   developing   cloudconditions   and   then   reach   targets   ofinterest and so that soundings can bemeasured routinely;

l Linking   airborne   observations   andnowcast modeling during flight so thatoperations   can   adapt   to   evolvingweather patterns;

l Downward   and   upward   irradiance

measurements associated with clouds,conducted   above,   below,   or   withinclouds, along with the ability to charac­terize   the   hydrometeor   and   aerosolpopulations and trace gases affectingthose irradiances;

l Coupling   of   trace­gas   measurementswith   studies of   clouds  to   learn  aboutentrainment and detrainment process­es or other processes in clouds and todetect and follow cloud­processed air;

l Use of a Microwave Temperature Pro­filer and/or dropwinsondes to measurethe temperature structure of the atmo­sphere and so characterize   the  envi­ronment in which clouds develop;

l Use   of   pressure   measurements   incombination   with   the   high­resolutiondifferential­GPS   measurements   tostudy pressure perturbations associat­ed with clouds and other dynamic ef­fects   arising   from   pressure   gradientsthat have been difficult to study;

l Exploitation   of   new   hydrometeorprobes that offer the ability to measuresmall ice or drizzle­size hydrometeorswith   increased   confidence   and   so   toaddress questions related to the effec­tive radius of Cirrus ice particles or thedevelopment of drizzle in clouds;

l The   combination   of   a   W­band   radarwith   a   high   spectral   resolution   lidar,which   can   support   high­resolutioncharacterization of cloud structure andmotions,  cloud  boundaries,  and earlyprecipitation development.

5. AN EXAMPLE: A POSSIBLE APPROACHTO DETERMINING INDIRECT CLIMATEEFFECTS OF CLOUDS

A  key  uncertainty   in   predictions   and   under­standing of global warming remains that asso­ciated with the indirect effects of aerosols onclimate,   especially   the   effect   of   increasingconcentrations   of   cloud   condensation   nucleion   the   radiative   properties   of   clouds.   If   thealbedo of low clouds is increased by such in­creasing concentrations, this may reduce thewarming expected in a future climate. The re­mainder   of   this   paper   discusses   a   possibleapproach to study of this effect that would ex­ploit the capabilities of this new research air­craft and also the very capable research air­craft  available elsewhere,  including the BAe­146   of   the   UK   and   the   German   “HALO”aircraft   under   development   at   DLR.   This   isoffered  here  as  an  example  of   the  ways   inwhich a continent­spanning aircraft can beginto   establish   links   between   cloud­scaleprocesses   and   the   global   scale   needed   ifstudies are to be relevant to climate.

An   approach   to   determining   effects   on   aglobal scale might be along the following lines:

l Use chemical­transport  models (CTMs)  topredict   where   sulfate   aerosols   are   en­hanced.   Concentrate   on   areas   wheremodels predict that clouds have significantradiative impact, like the Sc regions of theCalifornia   coast   or   the   Chile   coast   andelsewhere.

l Test those predictions against observations(of CCN and sulfate)  in regard to position

and   amounts.   Aircraft   observations   areprobably needed for these tests; some in­formation can also be gathered from satel­lite   radiances,   esp.   over   the   ocean,   andfrom   satellite­lidar   observations.   Groundstations   in   the  aerosol  networks  are  alsopossible sources of information.

l (if   the   preceding   test   is   encouraging)Determine  if   the  CTM predictions  can beused  to predict  CCN concentrations.  Thisprobably   requires   CCN   measurementsfrom   aircraft,   perhaps   complemented   bymeasurements   at   ground   stations.   Thisstep   would   benefit   from   the   existence   ofmultiple   CCN   spectrometers,   intercom­pared or identical, for use on different air­craft,   because   the   task   probably   is   bestconducted   by   more   than   one   aircraft   inmore than one area.

l (if   the   preceding   test   is   encouraging)Determine   how   CCN   properties   relate   tocloud characteristics. This is probably bestdone by correlating sulfate predictions withsatellite­measured cloud albedo, bypassingthe CCN step ­­ but the CCN step would beimportant   anyway   for   developingconfidence   in   the   chain   of   cause­and­effect.  Aircraft  measurements  of   radiativeproperties of clouds, esp. albedo, may playa role here also, especially in studying thefine­scale variations in albedo.

l (if   warranted   by   the   preceding   steps:)Use predictions of effects on cloud charac­teristics   to  generalize globally  and so de­velop an estimate of   the  indirect  effect  ofaerosols on the global radiation balance.

Components of this study might be:

l A   chemical­transport   model   or   a   globalmodel   with   chemistry   incorporated.   Themodel     would need to represent meteoro­logical fields, sources of various chemicalsand aerosols,  and scavenging and  trans­port, in order to be able to predict trace­gasand aerosol fields over large areas. 

l Aircraft   studies   in   different   regions,   con­ducted in coordination and collaboration, toincrease the extent to which the coveragecan be considered representative of globalconditions. The GV is a good candidate forstudies   in   remote  areas  or   requiring   longrange. The BAe­146 provides superb capa­bilities   for   characterizing   the   aerosol,chemical,   and   radiative  properties.   HALOwould of course offer capabilities like thoseof   the  GV.   It  may be possible  to   interestother  groups   in  a   coordinated   study,   be­cause   of   the   obvious   importance   of   thisproblem.

l Satellite   observations   of   cloud   albedo,which would have a key role to play in ex­trapolating results over broad areas and indeveloping   possible   correlations   betweenaerosol­model predictions and satellite ob­servations   of   albedo.   (Indeed,   one   mightthink of undertaking the study only with thislatter step, but such a correlation would beless  convincing  without  verification  of   thesteps in the cause­and­effect chain.)

Acknowledgment: NCAR is sponsored by theU. S. National Science Foundation, which alsoprovided   funds   for   acquisition   andinstrumentation of this new platform.  

REFERENCES

Grubišić,  V., and J. D. Doyle, 2006: Terrain­induced   Rotor   Experiment.   Paper   9.1,  12thMountain Meteorology Conference, Santa Fe,Amer. Meteor. Soc., http://ams.confex.com/ams/pdfpapers/114664.pdf

Laursen, Krista K., David P. Jorgensen, GuyP. Brasseur,  Susan L.  Ustin,  and James R.Huning, 2006: HIAPER: The Next GenerationNSF/NCAR   Research   Aircraft.  BulletinAmerican   Meteorological   Society,  87,  896­909.

Stith, J, W. A. Cooper, V. Ramanathan, D. C.Rogers,   P.   J.   DeMott,   T.   Campos,   and   B.Adhikary,  2008:   Interactions   of   Asianemissions with storms   in  the  Pacific  Ocean:Early results from the Pacific Dust Experiment(PACDEX). This conference.

Table 1:  Standard Requestable Instruments

Measurement Instrument(s)

position, attitude, groundspeed

inertial reference units and GPS receivers, Honeywell LASEREFIII/IV with Garmin GPS­16

pressure Paroscientific Model 1000 Digiquartz Transducer, separate fuselagestatic buttons

temperature HARCO Model 100990­1 De­iced TAT Sensor (2 units/4 outputs);Rosemount Model 102AL TAT Sensor.

dewpoint Buck Research Model 1011C Hygrometers (dual units)

dynamic pressure  Mensor Model 6100 Digital Pressure Transducer

wind gust sensing Mensor Model 6100 Digital Pressure Transducers measuring differentialpressures between ports on the forward nose radome

aerosol measurements Condensation nuclei (water based) and differential mobilityanalyzer, scanning

stratospheric water vapor tunable diode laser system

cloud water content heated wire (King) probe, DMT, and Rosemount icing probe

aerosol size distribution PMI Ultra­High Sensitivity Aerosol Spectrometer

cloud droplet sizes DMT cloud droplet spectrometer

ice sizes and shapes 2D probe, modified for the high speed of the GV

Table 2:  Special­Use Instruments

Measurement Instrument / Developer

hydrometeor sizes 3V­CPI / Lawson, SPEC, Inc.

small ice crystals small ice detector (SID­2) / Heymsfield, NCAR

aerosol backscatter high spectral resolution lidar / Eloranta, U. Wisconsin

temperature profile microwave temperature profiler (MTP) / Mahoney, JPL

spectral irradiance, actinic flux HIAPER Airborne Radiance Package (HARP) /Shetter, NCAR

full­range humidity Vertical Cavity Surface Emitting Laser Hydrometer /Zondlo, SW Sciences

nitric acid, SO2, & others Chemical Ionization Mass Spectrometer / Huey,Georgia Tech.

CO, CO2, CH4, N2O Quantum Cascade Laser Spectrometer (QCLS) /Wofsy, Harvard

O3 ozone photometer / Rawlins, PSI

O3 (fast response) chemiluminescence detection / Campos, NCAR

organic trace gases  Trace Organics (TOGA) / Apel, NCAR

occultation sounding GPS full­spectrum receivers / Garrison, Purdue

aerosol composition Time­of­Flight Aerosol Mass Spectrometer / Jimenez,U. Colorado

aerosol particles from evaporatedhydrometeors, or total watercontent

Counterflow Virtual Impactor / Twohy, U. Oregon

radar reflectivity and Dopplervelocity

HIAPER Cloud Radar (HCR), a pod­mounted DopplerW­band radar / NCAR