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
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