48O JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VoLUME7 Performance of Some Airborne Thermometers in Clouds R.PAUL. LAWSON* Depertment af Amaspherir Sciemce,Uniiyoyomiag,Laranie,Womimg WLLIAM A.COOPER Narional Cene jr dbmotpheric Rerearch Bodder,Coorad (Manxriptreccived28Jaly1989,infnalform27November1989) ABSTRACT Theabiyfitensrmerttomerpeneindoodtudiedeinghoretcnnd permendTheoricpditonsofeectforetngndodfed,and trorpedtomnent Toitoreimmersonterone eNCARrow"hermomr ndheRoerout0ztroerrompredoaehothradiodomichmomer.The omptohododeheoeet ae oher.oee.heesde icnceheinesionherotebconewtinnedoudsndcurereosoweprtr Tdom0 hedhe eoohdoddsh mmeriorspnpdd fomt in und fom mermen usineconducviynsroldloeoofheimnenoerTheintfeconouencsofthes mesuremetero,priculayinaudesofentrinmentandofcoud beoyno,aedcsd The recent development ofa short-path radiometric thermometer(Nelson 1982) provides an alternative Most airborne temperature probes use a sensing cle- measurement of temperature that should not be af- ment immersed in the airstream. The temperature fected by sensor wetting. In this paper we compare 1,Introdoction sensed by such an "immersion sensor"is infuenced measurements from this new radiometric thermometer by several factors other than the static temperature of to those from some conventional immersion ther- the air. The predominant corrections are those caused mometers.Measurements collected by the NCAR King by compressional and viscous heating of the air and, Air in clear air and in stratiform and cumulus clouds in cloud or precipitation,by evaporative cooling if the used to evaluate the performance of the new ra- sensor is wet. The amount of heating is a function of are diometric thermometer,to estimate the magnitude of (true)airspeed,so corrections for this efect can be errors from wetting of some immersion sensors, and determined from fight tests in clear air.However,the consider the consequences of such errors on past cffcct ofevaporative cooling on a wetted sensor is more to and future studies of buoyaney and entrainment. diffcult to determine because it depends on how much of the sensor is wet.Lenschow and Pennell(1974)ar- 2.Background gued that a wet thermometer exposed to air that is heated by compression and friction near the sensor Following the Thunderstorm. Project(Byers and will measure the wet-bulb temperature of that heated air,and this wet-bulb temperature can difer from the Braham 1949),where wetting of temperature sensors temperature of the heated air (ie.,the "recovery tem- was observed, some airborne thermometers were de- to avoid wetting in cloud. In this paper,we perature")by as much as-3'C for a completely wetted signed briefy diseuss the performance of some of these early sensor at a true airspeed of 1o0 m s". thermometers.Lawson (1988)presents more detail and provides historical references that describe the early Present Afhliatios: Nationl Cemter forAtmospheric Research. thermomcters. The National Center for Atmospherie Reeareh is sponsored The vortex thermometer developed by Vonnegut by the Natioaai Science Foundation (1950)was based on vortex separation theory,as dis cussed in Eekert and Drake(1972),The vortex ther- Corresonde aurhoradterDr.R.Paul Lwsoa.Visitis Sc mometer is still in limited use (Vernekar and Mohan ertis,NatioaalCenter for Atr0spherc Research,MMML.PO.Box 1975); however,published evaluations of its perfor- 3000. Boulder,CO 80507-3000. mancc in cloud are not available. e 1990 American Meteoroiogloal Socicty Unauthenticated | Downloaded 04/14/25 02:58 AM UTC Usntherficted1Dowbadd 0W1w250:58 AMUTC uME199O 481 R.PAUL LAWSON AND WILLIAM A.COOPER at the surface of the sensor when there is no net heat The University of Chicago(R.Braham 1987,per- sonal communication)built a reverse-flow temperature transfer to the airstream.The recovery temperature is probe based on work done in Canada(Fraser et al. affected by the thermometer housing(which slows and 1952).Fight tests in the Caribbean showed that water- hence heats the air)and by the sensing element(which sensitive paper at the location of the sensing element is heated by frction and by additional deceleration of became wet in some warm clouds and in rain(R. Bra- the airflow in its vicinity).If the air in the housing is ham 1987,personal communication),Rodi and slowed adiabatically to a fraction f of the free-stream Spyers-Duran(1972) described the design of another airspeed Ue, conservation of energy requires that the reverse-fow temperature probe that is still in use,A air temperature will change from the free-stream tem- parallel design was developed in Canada,but mea- perature To according to surements from both the Rosemount and Canadian C π=T。tmc。 reverse-fiow thermometers in clouds with 2 g mliq- uid water content were about 2"C lower than the air temperature out of cloud. () where T is the temperature of the dccelerated air in Telford and Warner(1962) used measurements the housing, U is now the true airspeed of the aircraft, from an intentionally wetted sensor. They argued that C, is the spscifc heat of air at constant pressure and such a sensor will measure the wet-bulb temperature ra=1-2is the ""recovery factor"of the housing. of the air near the sensor,and this measurement can Then ro=(T-Te)/(T-Te),where 7isthe stag- be used(in warm clouds)to determine the environ- nation temperature at C(sometimes called the ""total mental air temperature. temperature").If the sensing element is characterized The Rosemount total temperature probe is widely by a recovery factorr, applicable at the slowed airspeed used in meteorological research and in military and fUo, the temperature of the sensing element will be commercial aviation,Although this probe was designed to provide some degree of inertial separation of cloud drops,it has been shown (Heymsfield et al.1979;Blyth et al. 1988)that the sensing element becomes wet in U v。 T=Z+ 2C。 T十v2C (2) cumulus ciouds.Blyth et al.(1988)presented evidence wherer=1-f2(1-r)isthe efioctive recovery factor indicating that,in supercooled clouds,possible wetting of the thermometer.This dependence of the recovery ofa reverse-fiow snsor caused barely detectable errors factor on f and r, assumes that frictional heating of of <0.5*C.Lawson and Rodi(1987),however,showed the air by the housing is negligible. While(2) defnes the recovery temperature under that cloud water reached the location of the reverse- low sensor(of the Rodi and Spyers-Duran design)in adiabatic conditions at the surface of the sensor, in ciouds warmer than freezing, and supporting evidence practice these conditions are rarely met in airborne for this conclusion will be presented in this paper, thermometry.For a platinum resistance thermometer, Many investigators have used measurements of the additional errors result from conduction of heat from temperature of cloudy air in their studies of clouds. the housing to the sensor,self-heating(caused by the For example, the calculation of the buoyancy of cloud current used to measure the resistance),heating of the parcels is based on the difference in virtual temperature airby the housing,and radiative heat transfer,Resulting between the parcel and its environment, so measure- errors have been discussed by Doebelin(1983)and ments of buoyancy reported in the literature are de- Benedict(1984) in general terms,and by Lenschow pendent on the validity of temperatures measured in (1972)and Lawson(1988)for aircraf applications. cloud. The magnitude of the uncertainty caused by Lawson(1988)discussed the associated measurement possible weting. typically I-2°C,is often comparable uncertainties,and argued that these contributions can to the measured buoyancy.The accurucy of measure- te negligible in well-designed temperature probes(al- ments of temperature is also of critical importance in though they may afect the characteristic response studics of rates of cntrainment or sources of entrained times). air in clouds.The effects of possible sensor wetting on At an aircraf spced of 100 m s,compressional these studies depend on the type of temperature probe and viscous heating will warm the air approaching an used,the temperature,and the aircraft on which it was immersion thermometer by about 5°C(if re s 1). installed. We wil return to these considerations (in Because this compressional heating occurs in a few section 6) after the errors caused by sensor wetting are milliseconds,while the time constant for response of discussed. the cloud vapor feld to changes in ambient conditions is typically a few seconds (e.g, Politovich and Cooper 3.Theoretical discussion of effects caased by sensor 1988),droplets cannot evaporate fast enough to sat- urate the air.Cloudy air reaching the snsor will there- wetting fore be subsaturated,and evaporation of water from a The recovery temperature of an immersion ther- wet sensor will lead to cooling An erroneously low mometer,T,is the effective (ie,average)temperature measurement of temperature will be obtained if the Unauthenticated | Downloaded 04/14/25 02:58 AM UTC UeutheeficdedIDowabadd 0WI425Q2:s8 AMUTC 482 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY measurements are treated according to(2),which as sumes that the sensor remains dry. VoiuME7 One can insert(5)into(3)and use the Bedingfeld and Drew(1950)relationship for the ratio of heat-to- Dry convective heat transfer at high velocity has been mass transfer coefcients(as did Lenschow and Pennell investigated for common aerodynamic shapes(e.g 1974) to obtain Eckert and Drake 1972; Kays and Crawford 1980). Lenschow and Pennell(1974) combined these effects and the theory of wet-bulb psychrometry to determine the cffects of wetting on an airborne thermometer,They where 工b工, 6) argucd that the error caused by werting of a sensor (assumed to be dry) is the difference between the wet- bulb temperature of the sensor and the recovery tem- perature. This difference is the result of warming of 6L (Sc/Pr) P (7) the air as it approaches the sensor, which causes the is the psychrometric parameter,Sc is the Schmidt air to be subsaturated and leads to evaporative cooling number and Pr is the Prandtl number.The quantity of the wet sensor. (T-T) is the error caused by sensor wetting.and gained by forced convection exactly balances the heat Equation(6)is similar to the classical wet-bulb Lenschow and Pennell(1974) assumed that the heat its absolute value is oqual to the wet-bulb depression. iost due to evaporation of water from the surface of cquation, the sensor,and used the first law of thermodynamics to write the energy equation for a wetted sensor as T—T。= hS(T,-Tab)=Lme (3) 一1 AP。 (ex(T)-eo) (8) where the prime denotes quantities at low-velocity.In where h is the convective heat-transfer coeffcient,Sis (6),Treplaces Te of(8)and the free-stream vapor the surface area of the sensor,To is the temperature pressure has been multiplied by the factor Po/P,as of the sensing wire,m, is the mass flow of water vapor is appropriate in a compressed airstream near the sens- reguired to provide cooling through evaporation that ing element. baiances the heating due to forced convection, and Figure 1 shows representative magnitudes of the er- Lo is the latent heat of vaporization. rors in temperature measurement that would be cused Lenschow and Pennell(1974) obtained a second by complete wetting of immersion sensors.In this fg- relationship between the mas fiow of water vapor and ure,we have used the pressure ratio P/Pa in(6)that wire temperature from mass balance at the surface of corresponds to an adiabatic compression to a stagna- the sensor: tion point, as would be appropriate for a thermometer 空=h2二e 一Q withfe0 orre 1.'Figure 1shows that our calcu- (4) lations of Tt-T,are typically 20% smaller than those obtained by Lenschow and Pennell(1974)forr=1. where h. is the mass transfer coeffcient,qs is the free- Errors from sensor wetting can be about 1-3°C at air- stream specifc humidity,and qois the specifc humidity speeds of 1o0 ms',for a sensor with a recovery fictor atthe surface ofthe snsor;ie.qo=ee,(T)/P,where near unity and for temperatures from -20 to +20°C. e is the ratio ofmolecular weights(water to air),e(Tb) The magnitude of the error is predicted to increase is the sturation vapor pressure at the wire temperature with airspeed, recovery factor, and temperature. and P,is the total pressure at the surface of the sensor. 4.Instrumentation and sources of data Equation(4) can also be written as a. Ophir radiometric thermometer h P。 e(T) (5) The radiometric thermometer used for this study was designed and constructed by Ophir Corporation where es and pa are the water vapor pressure and of Denver,Colorado.The instrument senses the spec- total pressure,respectively,in the free airstream. tral radiance at a wavelength of 4.255 um,an absorp- At this point in the derivation,Lenschow and Pen- nell(1974) substituted the ratio of temperatures (T,/ tion line of COz, and the eficctive temperature of the volume can be determined from this spectral T)for the ratio of pressures(Po/P)in(5).This is emitting radiance through use of Planck's law.The design and valid only if the air density remains constant,but this is not the case for air compressed adiabaticaly(on the order of 50-200 mb)at fight,spceds of 100-200 m Te hih reoovery fctor ofte Rosemount thermometer,0.986. s.The physical basis for their interprctation of the iodicates that this analysis aill apoy to that instrurent,The rcovery effocts of sensor wetting is not changed,but the efiect fhctorafthesnsing eement,apatnum wire,ispeobablysgrilicnly on quantitative predictions is not negligible,as shown lessthan unity,and(2)indcatesthatthe high overallrecovery fctor can only be achieved with low f. in the following discussion. Unauthenticated | Downloaded 04/14/25 02:58 AMAMUTC UTC UoeniheeictedIDownbadd 0W14252-58 R,PAULLAWSON AND WILLIAM A,COOPER JuNE 19SO 483 possible because no thermal relaxation of sensors is involved(although the length of the sample volume limits the usefulness of measurements spaccd much a. Lenschow 8 Pennelt,1974 {eavotian 2b) closer than about 1O m). Figure 2 shows the basic components of the Ophir radiometric thermometer. Radiant energy is band- b,Present woek (equaticn 6) o limited by an interferencc filter(A) and focused by an off-axis parabolic mirror(B)on a lead sekenide detector (C).The radiance reaching the detector comes alter- ( o5 皇 nately from the external atmosphere or, refected by a To-i5c 4O go 2o 6 mirrored chopper wheel (D),from a blackbody ref- erence cone(E) in thermal contact with outside air through ventilation ports(F).A heat sink and ther- moelectric cooler (G) control the temperature of the detector.Four solid-state temperature sensors monitor the temperature of the blackbody reference.The ref 2CO TRUE AiRSPEEo (ms" erence temperature used,Tre, is obtained from a weighted average of these four measurements, weight- ing the two measurements near the tip of the reference PG.1.Temperature error(T-T)forswetted snsor with? cone only 25% as heavily as those near the opening 1safnetion oftme airspee at-15and +15°C,using(2S) Tbe change in radiometric signal as the detector alter- from Lenschowand Pennell(1974)and(6)from the presemt work. nately views the blackbody reference and the outside air volume is used to determine the difference between theoretical basis for the instrument are documented in Ter and the outside air temperature, by inversion of the Planck formula for spectral radiance. The Planck formula is have been discussed by Albrecht et al.(1979)and Ni- 2hc2 more detail by Nelson(1982). Other radiometric measurements of air temperature cholls et al.(1988).The latter reference describes mea- surements from an instrument operating at the same P(λ,T)= xxesr_iy (9) wavelength as the Ophir radiometric thermmometer, where h is Planck's constant,cthe speed of light,λthe while the former is based on measurements at wave- wavelength,and k Boltzmann's constant.The differ- lengths near 15 um,COz is a stronger absorber and ence between the spectral radiance of the air and that emitterat 4.255 am than at 15 am,so the sensed sample of the blackbody reference is determined from the volume is located closer to the aircraft.For a wave- voltage difference,Y, from the lead selenide detector length of4.255 um at 500 mb in clear air,90% of the (after using a lock-in amplifer and low-pass filter). signal comes from within 10 m of the aircraft(Nelson 1982),while the corresponding depth at 15 um is about 200 m(Albrecht et ai.1979).A sensed volume ex- tending over about I0 m is long enough to displace most of the sample from the region affected by airflow around the aircraft but short enough to avoid corrcc- tions for pointing ange, temperature gradicnts, etc, Water is a very strong absorber at 15 am(3.6 m- versus about 0.3 m-1at 4.255um,Irvinc and Pollack 1968).so that radiometric thermometers operating at this wavelength sense mostly the cloud dropiet tem- perature in clouds. On the other hand,the 4.255 am radiometric thermometers should have signifcant contributions from cloud droplet temperatures only in very dense,growing clouds,where the droplet temper- ature is thought to be within 0.1°C of the air temper- ature:ct Neiburger and Chien(1960)or Pruppacher and Klett(1978). The primary theoretical advantage of the new 4.255 um radiometric thermometer for meteorological re- Fc,2Principalcomponents ofthe Ophir rdiometric thermom- eter(A)inierteence flter;(B)pboicmirror;(C)lea sekeide cloud,while immersion snsors may be infuenced by dtoctor:(D)mirored copperwheet;(E)blckbodyreferenee cone; wetting of the exposure sensors,Fast response is also (F)ventiation ports(G)heat sink and thermocloctric cooer. search is that the measurements should be reliable in Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherticted1Dowbadd AMtUTC 484 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY voT The diference in spectral radiance,AP,is determined cated in a housing designed to avoid impacts with hy- from aV+a?V? △P b+bV drometeors. The sensing clement used in the reverse- fow probe consists of a platinum wire wound in a (1O) spiral,The recovery factor for the reverse-fow ther- mometer mounted on the wing of the NCAR King Air The quadratic term in(10)is an empirical correction has been determined to be 0.625 ±0.015,and that for Rosemount probe is0.986±0.012(Cooper 1987). for non-linearity in the optics and lead selenide detector theOther instrumentation used for this study was stan- (cf Wyatt 1978).The constantsa,az,b,and bwere dard equipment on the NCAR King Air. Wind was determined by calibration of the radiometric detector measured using an inertial navigation system and a in an environmental chamber,and the voltage v gust-sensingsystem(Brown et al. i983).Cloud (measured across a bias resistor in the detector cathode radome water content was detected by several instruments in- circuit) is used to correct for variations in gain as the cluding a Johnson-Wiliams probe,a hot-wire probe dark resistance of the detector varies with ambient built according to the design ofKingetal.(1978),and temperature, a forward scattering spectrometer probe(FSSP).The Tbe spectral radiancc of the air having temperature measurements of liquid water content have been ad- Z。isthen P(λ,To)=P(λ,Tac)+ △P, justed to yield zero when the FSSP indicates that no (1) cloud is present,Recent tests by King et al.(1985) that the King probe is aocurate to within about so the Planck formula(9)can then be inverted to give indicate 10s for measuremenis of liquid water content from 工 0.5 to 2.0g m-3.Humidity measurements from dew- 12 point sensors and from a Lyman-alpha hygrometer were available,and precipitation was measured by hy- drometeor spectrometers covering sizes from 5o to 64OOgm. b. Orher instrumemtarion c. Field programs Two immersion thermometers were used in this The data used for these studies were collected during study,a Rosemount Model 102E2AL total temperature a field project conducted for other purposes.In the fai probe(non-deiced model) and a reverse-low ther- of 1985 fights were made in small cumulus clouds mometer built at NCAR according to the design of ovcr the Gulf of Mexico,from a bae in Louisiana,to Rodi and Spyers-Duran(1972).The principal com- collect data for reconstruction of felds of liquid water ponents of these thermometers are shown in Fig. 3. content from radiometric observations(Warner and Each uses a platinum resistance wire 2s um in diameter Drake 1988).Penetrations through regions ofcumulus to sense air temperature, and in each the sensor is lo- clouds warmer than freezing were made during this 5te scoie 5(em SCGe Fc,3.Pincipalcompoentoftwoimmerion hernometersuodinhs tudy,the Rosemount otemperturepoke(lef)andtheNCAReerowpot(ed)Aeshrohpo A)andisexhausedhrouehports(B)aercomininthermlentetwitplinumwiepsor (C).Thepesre dignedtosepartecoud drometeos(D)fromthearramechin the sensing ciememt Unauthenticated | Downloaded 04/14/25 02:58 AM UTC Uentherficted1Dowbadd0W142502:58 AMtUTC JuNE 1990 485 R.PAUL LAWSON AND WILLIAM A,COOPER study, and they have formed the data set used in this Zo study.The NCAR King Air was fiown through cu- mulus clouds haying liquid water contents ranging to values>2 g m-,and through light to moderate pre- 5 cipitation. Data have also been, collected in other programs conducted in New Mexico and in Colorado, but they will not be discussed in this paper.(The Ophir instru- ment malfunctioned in those programs,apparently as a result ofearier damage to the unit caused by ingestion of water)A new,modited version of the radiometric thermometer was used in 1989 on the NCAR Electra in the Experiment on Rapidly Intensifying Cyclones in the Atlantic(ERICA),flown in wintertime from Maine over the Atlantic Ocean. Preliminary analysis of measurements from that project show general agreement with the results reported in this paper when O 5 2O RFT[oC] the radiometric temperature measurements are based Fig.4 forthe Ophir ndiometric themometer(ORT). on a single calibration to the Rosemount thermometer ThePo.5.Asin mean for the ORTwas 6.46°C.and the best-fit line minimizing in clear air. the distancetotheploted pointswasORT-0.116+0.97s3(RFT) 5.Observations a. Clear-air inierconnparisons cm3,or the liquid water content never exceeded 0.0s gm-.The measurements shown are each averages of Figure 4 shows comparisons between the Rosemount 50 samples taken over intervals of one second, after total temperature(RTT) probe and the NCAR reverse low-pass ltering(with a four-pole Butterworth flter) fiow temperature(RFT)probe for fight in clear air. with a cutoff frequency of 0 Hz, so cach represents To avoid effocts of evaporative cooling afer exit ffom the average of about five independent samples The cloud,data are shown for which the droplet concen- regions used were mostly nonturbulent areas far from tration during the preceding 30 s never excceded I clouds,so that the data do not contain much small- scale variability in temperature. The agreement be- tween the Rosemount and reverse-flow thermometers was excellent: The diference between the mean ter- 2o peratures was 0.0sC and the standard deviation ofthe difference was 0.07C for more than 10 000 data points. The excellent agreement is partly the result of calibra- tion of both sensors in the same laboratory to the same standards,but it provides an example for comparing o similar results involving the new radiometric ther- mometer. Figure 5 shows corresponding data for the RFT and the Ophir radiometric temperature(ORT).In this cas, the diference in the means was again 0.0s°C,and the standard deviation was slightly larger at 0.15°C.Figure 6 shows histograms of the diferences in temperature for the clear-air data of Figs.4 and 5.About 95% of the temperature measurements made by the Rose- o RFT[oC] mount (Fig.6a)were within 0.1s°C of those made by the reverse-fow probe,while 95% of the measurements from the Ophir thermometer(Fig.6b)lie within 0.3°C PG,4.Corresponding measrements of temperature fom the of the measurements from the reverse-flow probe. Rosemount toeal temperature (RTT)and the reverse-0ow temper- ature(RFT)probes Ech point representsthe averc of50sampies Uncertainty analyses(eg,Lawson 1988:Cooper spanning one sacoed.Only poins at least 30s aferthe ltest coud 1987) indicate that the expected aocuracy of the im- penetrtion are piotted,to avoid effcts af wetting in cload,Durirs mersion and radiometric thermometers is about 0.3°C oee researeh fight(spsnming srouad4h)there were 10433 sch these(quiescent) atmospheric conditions, so the points only ev tenth poia au poted in the feure,The means for during the above intercomparisons is within were6.49C(RFT)aed6s4C(kTT),and thekest-Hr line mini- agreement mirgt distancetothepotted poitsRTT-0001+10076 the estimated accuracies of the probes.For measure- (RFT).(Data from7November1985,1208-1526 C5T) ments in clear air, with one-sccond resolution,this Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC 486 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 5ooo Oo 4ooo 8O 3ooo o 三2oOG ooo O Zo O o.o O_5 voiuME7 dence of the temperature diference on liquid water content,shown in Fig.8.was strong, and signiicant differences were observed for liquid water contents of 1-2g m.Although the average offset is larger for the reverse-flow probe than for the Rosemount probe,the sensitivity to liquid water content was higher for the Rosemount than for the reverse-flow probe. In both cases the errors from the immersion sensors(if the Ophir radiometric temperature is correct)were about -i"C at a liquid water content of about 2gm-. r-eT This sensitivity to liquid water content was not ex- 25oo CC 2ooo pected,The analysis ofLenschow and Pennell(1974), as modifed earlier in this paper,predicts a(maxirum) temperature error assuming the sensor is completely 6O 15oO 加C wetted.The predicted cooling will not occur,however, unless there is suffcient liquid water contacting the wire to maintain the assumed evaporation rate.The appropriate heat balance equation that gives the liquid 5oo LO 2o C5 o.o C.5 LO water content required to maintain wet-bulb conditions is obtained by cquating the sensible heat transport to the latent heat release,as in(3); oRT-RT πKNu(T,-Tb)=(Xd/)*LoUed (13) ofcloud)messurementown in Fig 4and 5(a)Diference be where x is the liquid water content,e is the fraction of tween the Roserount(RTT) and evere fow(RFT)thermomeiers liquid water content that strikes the sensor,K is snd(b)dikreece btuen the Ophi(ORT)and reere-ios(RFT) the therometers The dnshed lines sow the cumuhtive pereent salkr the thermal conductivity of water vapor in air,dis the than the potted value,ploted reative to the cale an the rght. diameter of the sensing wire,and Nu is the Nusselt PG.6.Histograms of dikrence in temperature forte ame(out- number characterizing the enhancement ofheat trans fer by ventilation. The asterisk denotes the critical value agreement thus lends support to the validity of both of the product required to maintain wet-bulb condi- scts of measurements because the techniques and cal- ibrations are completely independent 25o oo 2oo 8o I)COMPARISON OF MEAN VAUES i5o 6o Figure 7 shows histograms, similar to those in Fig. Oo b. Measiurements in warmt clouds 6,for measurements in clouds warmer than freezing. These mean temperatures were obtained from all mea- surements made when the droplet concentration was >20cmon one flight(7November 1985).The mean valuc for in-cloud measurements of temperature from the Rosemount thermometer(Fig.7a)was about 5o LO 2O O5 o_o C.5 Rr-FT 0.26°C above the mean from the reverse-flow ther- mometer, and was within 0.02C of the mean from the Ophir thermometer(Fig.7b).The standard devia- 2oo 8o about0.18°C(RFT-RTT)and0.36°C(ORT-RTT or ORT - RFT).These results show that,even in 5o 6o oo o 5o 2O tions of the measurements about these means were clouds,most of the measurements were in good agrce- ment. Although the differences became more variable in cloud,the increased small-scale structure of the temperature feld there may have caused part of the increase in standard deviations. The average liquid water content in these in-cloud regions was only about 0.2 g m-?,so most of these _iG _O5 oO oRT-RFT o5 tO Fio.7.Iistognms,in the sare sormat as shown in Fig 6,for the 1849 measurements made"in-coud"(where the droplet concemtra measurements were from very thin clouds.The depen- tioe was at least 20 cm3). Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC JuNE L99O R.PAUL LAWSON AND WILLIAM A.COOPER 48z olds number for a 100 ms! airfiow past atransverse cylinder(e.8,a simple wire)with diameter of 25 um is about 1s0,resulting in a Nussclt number of about 6.An estimate2for(xe)*can be obtained by,using this Nusselt number for a simple wire in(13).For G temperatures ranging from-20 to+20°C,an airspeed of 100 m s-,and a recovery factor of0.625(ie,the revere-low probe),typical values of(xdf)" are about (1a do) 0.1-0.2g m-3.According to(2),this recovery factor requires f>0.6,so the continued dependence oftem- perature error on liquid water content up to values of at least 2g m(cf Fig.8) sugeests that the collcction effciency with which cloud droplets strike the probe and sensor is only about 0.1 or less, and/or that the Nusselt number is larger than for a simple wire.Un- fortunately,snsitivitytoc reduces the predictive value O.o O.5 t.5 LwC [g m-s] 2.o 2.5 of equations like(6), because it is likely that the col- lection effciency is a function of droplet size and so will vary in different clouds. 2) OBSERVATONS OF UNDILUTEDCLOUDPARCELS Figure 9 shows some measurements made during a penetration about 1 km above the base of a cumuius cloud.The measurement of liquid water content shows a uniform region in the center of cloud that was ap- parently undiluted by entrainment. Other measure- ments not shown here,such as droplet concentration E and intensity of turbulence,support the existence of an undiluted core.Another research aircraft fying be E low cloud basc at this time measurcd a temperature of 2t.6°C and a dewpoint of 18.8"C.These values require 18o) a lifed condensation level of947 mb and a cloud base temperature of 18.2C, and are similar to direct ob- servations of cloud base on this date by the NCAR King Air in other nearby clouds. The temperature predicted for adiabatic ascent from 2 o.o O.5 1.o 1.5 LwC [g m-33 2.o this cloud base to the observation level ofthe King Air is about 12.5°C,and the corresponding liquid water 2.5 content is about 2.0 g m-.As shown in Fig.9.the mcasured liquid water content was very close to this Fo.8.(a).The dirence between measurements fom the Ophir value in the irst part of the penetration,and the ra- and revere-oow thermometers,ploted as a fuction of the liquid dionetrc temperature was in sood agreement with that water content(measured by aCSIRO King probe).(b)The cor predicted for adiabatic ascent.In contrast,the reverse- responding dferenee between meuremets from ths Ophir snd fow temperature was about 1°C colder than the pre- Rosemouat thermometers Data from the fight of the NCAR King dicted temperature.(The Rosemount temperature,not Air on 7 Nowember 1985. shown,was in close agreement with the reverse-flow temperature.) tions at the sensirg wire. The sensed temperature in cloud,Te, will then be T。=Top,(xd/)>(xt?)* =工,_ xeLfud otherwise, KNu (14) Aiso shown on Fig. 9 is the temperature difference expected betwcen the Ophir thermometer and the re- verse-flow thermometer ifthe former is correct and the (15) 7The ensorsin the reverse-tow and Rosemount probes are coiled tha Re snd N my actly te urr for these comples Morgan(1975) has measured Nu for tlow past a wires,so sersor confgurtions.For eampke,Zusks(1972)easured transverse cylinderto be Nu=0.58 Re?4?for35< Re vslues ofNa for airfo pat banksofotinders thar rnged apwards < 5000,where Re is the Reynolds number.The Reyn- ofan order ofmenitude aryer than for asimple trnsverse cylinder Unauthenticated | Downloaded0W142502:58 04/14/25 02:58 AM UTC UenthertictedIDowbadd AMtUTC 488 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VouME7 ADiABATIC LWC ADIA日AT 出 DR N 3 2 aA oasERvEp KEeSGCaEve TMEoRETiCAL sFikE I4o83o i4oe4o Ao85o TiME tcST Po,9.Timesriesofmeuremen rcorded durngpeoetrtionteNCARKingAirafa undlte cosnmcdodeNo7oemb95Tett uid troet eompued sine mermens akent doud s y the NCAR B Tepoom)heoh memetr(RrT).andscoprdtredtmpertredrncetuenheRFTandtheOphir rdometric thermometer.(AT= RFT-ORT.) latter is affected by sensor wetting according to(6). The agreement between the measured difference and the theoretical value supports the interpretation that 3)EVIDENCEOFEVAPORATIVECOOLINGONCLDUD ExT Figure 11 shows an example ofa penetration through the reverse-flow snsor is wet,and sensor wetting ex- the top of a cumulus cloud,afer which the aircraft plains the discrepancy. Further support comes from emerged into air having a dewpoint depression of11°C. the rapid drop in temperature measured by the reverse- If the immersion sensors become wet in cloud and re- flow thermometer on cloud exit; this drop was not in- tain some water as they enter the drier environmental dicated by the Ophir radiometric thermometer,and is air,evaporation of that water should produce a tem- likely caused by evaporative cooling as the wet sensing porary false dip in temperature.As plotted in Fig. 11, wire is carried into drier air outside the cloud. cooling of the immersion sensors would produce de- Other penetrations of undilute regions of cloud pro- creases in the differences(RFT-ORT) or (RTT duced similar temperature differences when the liquid -ORT).The figure shows clear transient decreases of water contents were high.Approximately the same ef- the type expected at cloud exit,as marked with arrows, fect ofliquid water content as shown in Fig.8 was also and those transients decay with time constants of <i evident in measurements made during rapid climbs s. Many other examples were found (cf. Cooper 1987). through cloud base.Figure 10 shows measurements Similar searches for effects of evaporative cooling in for which the corresponding measurement of liquid measurements from the Wyoming King Air resulted water content during the climb was within 0.0s gm3 in a different trend (Blyth et al.1988),The Rosemount of the value expected for adiabatic ascent.In each case, 102 probe on that aircraft is a deiced version,and that the solid line represents adiabatic ascent calculated for thermometer exhibited 1-2°C dips at cloud exit that the conditions measured just below cloud base.While were similar to those in Fig. 11.However,no similar the Ophir thermometer measured values consistent effocts were found in measurements from the reverse with adiabatic ascent, the Rosemount thermometer fiow thermometer, although it was identical to the (and reverse-flow thermometer, not shown)measured NCAR probe and was mounted similarly on the air- values systematically too low.The liquid water content craf.A signifcant difference was that all the data ex- at the top of the ascent was about 0.2s g m3,so the amined were from supercooled regions of cloud,while departure of about 0.2°C is consistent with the trend the data from the NCAR King Air used in the present ofFig 8.In this and many other climbs through cloud study were from cloud regions warmer than freezing. base,there was no sudden temperature jump at cloud base as might have indicated the onset of sensor wet- c. Measuremients in cold clouuds ting Instead, the effccts of wetting on the immersion Some results of studies ofthe reverse-fiow and Rose- mount thermometers in supercooled clouds were de- sensors appeared gradually during the ascents Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC uN19ao 489 R,PAUL LAWSON AND WILLIAM A.COOPER recovery temperature indicates if supercooled drops will freeze on the probe housings and sensors,as expiained in the following section.)The measurements from all three thermometers agreed well during the climb in clear air(e-g,at t023 CST).When the temperature 5OO was above 0°C(1025-1026 CST),both immersion thermometers measured temperatures in clouds about 0.5°C below those from the Ophir temperature. How- 4oo ever,there was a clear change at the freezing level,and after 1031 CST the measurements from the reverse. in山i山7v fow and Ophir thermometers were within 0.3°C of each other,while the Rosemount measured a temper- ature 0.5-i.0°C lower.These observed tendencies are further explained by additional measurements in the following section. t5oo 55 6,o 6 7.O 5 B,O RTT [oC] 15oo d Measurements with a conductivity sersor To gather additional evidence regarding weting of the reverse-flow sensing element, a simple electronic device was fabricated and placed in a reverse-flow housing at the location of the sensing eiement. This device consisted of two bifurcated gold conductors spaced about 50 um apart and etched on a ceramic substrate.The conductivity between the two conduc- tors was measured by a high-impedance MOs/FET operational ampliter. The eiement and the circuit used are shown in Fig. 13. E Bccause the conductivity of air is much less than 14OO that of water,wetting of the element produces a dra- matic change in conductivity. Wben the conductivity 2 t5oo 5 6.O 6, Z.O Z5 8,O ORT [OC] Fo.10.Temperature asa function of alitude for a rapid scent throa coud bs 1302CST on 5Novemer1985.Al mta- surements shown re for points where the iquid water oontent wss C ithin 0.0s g mofthe value expected foradiabatic scent The temperature expected fr zdiahatic ascent from the measured cloud as isalo shown a)RTT:Rosemoumt totaltemperture;b)ORT- Ophir mdiometric thermometer. scribed by Blyth et al.(1988),These studies concluded that the reverse-flow probe provided accurate mea- surements in such clouds,although there was evidence that the Rosemount probe was affected by werting of the sensor.Additional evidence supporting these con- clusions was obtained in the present study. :5o ;4o TME [s] 5O FG II.Liqvid water content (LWC)measured by aKing pobe Figure 12 shows measurements from a climb of the and diferences between meaured temperatures Neasurcr ensane fom a ps trouhaccd a temperature ofabout+1OC oe7 NCAR King Air through astratiform cloud. The liquid November 198sa 1i30CST.Aroeindicte empies oftransient water content varicd from 0-0.5 g m-?,and the re- temperature difrences at coud exit,cued by evaporative cooling covery temperatures ranged from +6° to-2C.(The ss te wet immersioe sensoes enter dry sir. Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC 49O JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOOY 【 VouusE7 【 AT _ RFT LwC io25 O2 TiME tCST} 目o o2z io26 TiME [CsT) 3 告 oRT RFT b 2 L AT A 3cwa oSq o52 TiME (CST) Po.12.seleeted sgrents of mesurement rcoded during cimb bythe NCAR King Air throueh he feeinsketfmclodTmpermeonheR totliempeturepoke(RTT)theCARer-pwherometer(RFT)andheOph ndiometrc therometer(ORT)are referenced tothe letsle,ahk liguid watereontent(LWC) mesurements fom theKingprobe are efereced to the rehfsale.Tietup sripshown atthe topremerementmdeinclrsrandwrmcoudwhiiethebotomsiparmesurement msde mostly in supercooled cioud element was exposed in the laboratory to water droplets scribing this sensor was presented by Lawson and Rodi of about 10 am diameter,the conductivity changed by (1987). factors of 10*-103,The response to ice was also tested Two identical RFT housings were mounted by Col- by spraying a fne mist of supercooled droplets on the orado International Corporation on the Particle Mea- sensor; this usually produccd changes in conductivity suring Systems Bcechcraft Baron for operations in the by factors of 102-io*,but the results were variable and Precipitation to Augment Crops Experiment (PACE) sometimes no change in conductivity was observed. in central Illinois.One housing contained the usual The conductivity sensor thus provides a good indicator platinum resistance wire,and the other contained the of wetting in warm cloud,but the evidence is not con- conductivity snsor.Figure 14 shows results from some clusive in supercooled cloud. More information de- cloud penetrations. The temperatures shown in, this case are the temperatures of the sensing wires,without compensation for dynamic heating; this temperature better identifes the parts of the cloud where the water striking the sensors and housing is supercooled. At the typical truc airspced of the Baron, about 90 msat 500 mb,the diference between recovery and free gs stream temperature is about 2.5°C for a reverse-flow probe(r= 0.625). During the two penetrations flown where the tem- perature was above freezing,the signal from the con- ductivity probe was well correlated with the iquid water content. There were also strong evaporative cooling effects on the Rosemount probe,and weaker effects on the reverse-flow probe.In contrast,the data in Fig.14 show no signifcant signal from the conductivity sensor during passes in supercooled clouds(where the mea- sured temperature was -3°C, and the liquid water Po.13.Schemaric diagram ofelectronics used in the signal con dtioner fr the conduativity pros(top),with the cooductivity ele ment shown at the boetom Aetual size ofthe ckement is about I by 3c。 content approached 1gm),The data shown are rep resentative of several similar passes in superoooled clouds. The indications from the conductivity sensor are that no water reached the location of the temperature cle- Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC 491 R.PAULLAWSON AND WILLIAM A-COOPER JuNEISgO a 三 E 三 M I755 se 5z z5e z5g 8oo i5eo TME tCoT 56i 562 三 三eo E y 557 i5e i559 Po,14.Time seresofmesremeats rordedin cumulus cloods during PACE !986,were the(eoovery)epersoftheimmerio theroometerswerermertan fering(a),and odrhnfeeing(b.eoondetitymesremensweetusinaoonduetviyeemen (towniF13)pacedinanNCAR reer-owhosingthelocioofthepltinumwire sensoc, ment in supercooled clouds,There are, however,un- watch the motion of water along the surfaces of the certainties associated with the expected conductivity probe.Two qualitative results from the studies in wind of ice(e.g,Hobbs 1974),so it is not possible to nule tunnels were apparent, First,the airflow through the out the possibility of some(frozen)water on the snsor. probe was very turbulent,not having a laminar char- The evidence is clear that water reaches the location acter as would be desirable for separation of cloud ofthe sensor in clouds where the temperature is above droplets.Second, water tended to accumulate on the freezing outside of the housing(cf. Fig.3) and move down- stream until reaching the cylindrcal opening at the e. Wind tannel ohservatiowms back,then move around the opening and accumulate In an cffort to study the reason for the ensor wetting just inside that cylinder.The accumulated water was and the difference between supercooled and warm caught in the turbulent airflow and sprayed in a random cioud regions,the reverse-fiow probe was operated in direction,sometimes back into the housing. This ap- an improvised wind tunnel (capable of 50 m s)and pearod to be the mechanism by which the snsing wire exposod to a cloud of droplets produeed by a spray became wet device designed for the calibration of liquid-water me- This sequence also explains why the housing appar- ters.The probe was operated where it was possible to ently prevents water from reaching the sensor in su- Unauthenticated | Downloaded 04/14/25 02:58 AMAMUTC UTC UoeniherictedIDownbadd 0W1425Q2-58 492 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY percooled cloud. When the water is supercooled, it VotuwE7 eGiCup M5E cannot move along the surface of the housing and re- mains where it colides building up rime on the leading cone of the housing The freezing of collected water prevents its motion to the rear opening and its subse- quent entrainment into the turbulent airflow. 6. Sclentific implications DaTA uSIMG EVER FLO EMPERATURE a. Emtrainment Paluch(1979) introducod a method for estimating the source and amount of environmental air entrained into clouds,The method is based on calculation oftwo parameters that are conserved in moist adiabatic con- vection,the wet-cquivalent potential temperature (6,) 3C 3io and the total water mixing ratio,C.Bccause values of 52o 34o 55O gk 6,and C,for a mixture ofair parccls are (approximately, in the case of0)proportional to their contrbutions to the mixture,linear piots of C, versus 8, can be used to deduce sources and quantities of entrained air. In most cases, the measurements of humidity have OuD aA inadequate accuracy for thes methods(for observa- tions in cloud),and the humidity is instead determined frorm the temperature of the asumed-saturated cloud. In these cases,the only independent measurements en- tering the calculations are those of temperature,liquid E baTa uSNG water content, and pressure.Humidity enters both variables,so both are thus very sensitive to the mea- RADiOMETRiR TEMPERATUE surement of temperature in cloud and the errors re- sulting from erroneous temperature measurement will produce highly correlated errors in O,and 6 During the studies over the Guir of Mexico,the NCAR King Air often penetrated regions of warm cu- mulus clouds about 1 km above cloud bae,where the cloudy air over much ofthe cloud pass was only slightly oO 3io 32o 3o 34o 35O 6ax Fc.15.Paluch diaram shoutng plot of total sater conttat(C) diluted by environmental air.These data offer an op- erws aetequivalent potentis tomperture (9).Dsts were tecorded porunity to cxamine the initial cfccts of the mixing duriss pentrstion o'sur curuls coeairine t undittsd core.me process in clouds with no precipitation or ice.Figure previouly shoe i time-sries focmat in Fie.9. Temperatue ed to construct the top feure (a)were fom a reverse i5a shows data plotted as C versus 0,for the cioud surements probe,thought to be wet.The botom figure(b)shows corre- pass previously shown in Fig. 9.Data are shown from flow mesurements from the Ovhr rdioanerric thermoreter, ithe reverse-low thermometer and from the King liquid spoedis Measurements ofliquid water content were made bya CsIRO-King water probe. There is considerable scatter among the liquid water meter. data points,and the plot does not suggest a localized source of entrained air;there are even values suggesting that there are contributions from below cloud bas or onstrate that,in warm clouds,quite erroneous conclu- above cloud top. However, when data are used from sions could be drawn from thermodynamic analyses the Ophir radiometric thermometer, as in Fig,15b, based on the immersion thermometers. there is a pronounced reduction in the satter among Paluch(1979) used data from a reverse-tlow probe the data points,and indications that the observed air mounted on a sailplane,(This probe resembled that consisted of a mixture from cloud base and from near designed by Rodi and Spyers-Duran,1972,but was identical to it) In this case,the slow speed(<s0 the penetration level of the aircraft.Also,the data col- not lected in the protected core extend along a line very ms"')of the aircraf limits the temperature uncertainty near the cloud bae point,as would be expected if very to less than 0.5°C even if the sensor were wet,as can little mixing had occurred. In contrast,the corre- be demonstrated using(6),so the measurements from sponding data in Fig. 15a are displaced from the cloud the sailplane are not subject to the errors discussed base value,and the slope of the line is rotated toward here.Boatman and Auer(1983),Jensen et al.(1985), an entrainment source from below cloud base instead Austin et al.(1985) and Blyth et al,(1988)apalyzed of from near the observation level,These plots dem- data from a reverse-fiow probe mounted on an aircraft Unauthenticated | Downloaded 0W142502:58 04/14/25 02:58 AM UTC Uentherficted1Dowbadd AMtUTC JuNE 19So 493 R.PAUL LAWSON AND WILLIAM A.COOPER with a normal operatingspeed ofabout 100 ms-,and only considered data in the supercooled regions of cu- mulus clouds;the conclusions from this paper do not 323 us ci3o sugest a problem with any of these anaiyses or con- clusions. There are some studies, however,where the effects of wetting of the temperature sensors may be serious.LaMontagne and Telford(1983),for example, used temperature measurements from a Rosemount thermometer, and some of the measurements in Fankhauseret al.(1982)[presented therein by Cooper] are from warm regions of NHRE clouds where sensor wetting may have affected the measurements. Mc Carthy(1974)studied rates ofentrainment using mea- surements from a Rosemount probe, and Heymsfield et al.(1979)argued that these measurements may have been erroneous bccause of wetting of the temperature sensor. The present study indicates that temperature measurements from immersion thermometers are ofen erroneously low because of sensor wetting in clouds, and often do not have sufcient accuracy to support analyses that rely on the measurement of temperature in clouds. b. Buoyamcy Evaporative cooling caused by sensor wetting can lead to underestimates ofcloud buoyancy by 0.5-1°C, aoiusTED Cv 322 Roso 32 4eoom i4 sEPr iSz4 52O 5上GOUD LEaOiNG ED0 Lya J L 2o3 t2o4 TiME N GMT asindicated in Figs.8 and9.LeMone(1980)criticized measurements of buoyancy by Warner et al.(1979) Po.16.Time series of messuremens recorded during airer ofs warm cumulus coud observed in GATE(adapted on the grounds that the Rosemount temperature sensor penetration Lehone 1983).The virtual potential temperature was co- became wet and read too low in clouds.Because of from rensated for waer ioading(oa)s shown as fom LeMone snd also this problem,LeMone(1983) used three other esti- adjusted asing the relationship betwccn liouid water costent and mates of the buoyaney term that did not use direct mesred temperature ffom Fie Also shoap are mesrements measurements of temperature. The relationship be- of vertical wind s,and liquid water miing rtio t sing Johnson tween temperature depression and liquid water content shown in Fig.8 may differ for different clouds.How. Wiisms(J-W)and Lyman-pha(Ly-a)instrumemts ever, when this relationship is applied to the data of LeMone(1983)as shown in Fig.16,the adjusted the observed errors were found to be a function ofliquid buoyancy is about 0.5°C,and this is the same value of water content, and only reached the values predicted mean buoyancy deduced on the basis of other as- in regions with liquid water contents of about 2 g m sumptions by LeMione (1983). 7. Summary and conclusions The observed errors in temperature were found to be of order 1°C in such regions. Such errors can be sig- nifcant in studies of cloud buoyancy and entrainment, Some of the immersion thermometers used on re- Ackowledgerts. The authors express their grati- search aircraft become wet in warm clouds and read tude to Alfred Rodi,Ken Endsley,and Perry Wechser erroneously low as a result,An often-uscd reverse-flow of the University of Wyoming,to Don Lenschow and thermometer does not appear susceptible to these errors Margaret LeMone of the National Center for Atmo. in supercooled clouds, although the evidence support- spheric Research,to Loren Nelson and Todd Cerni of ing this conclusion is somewhat limited.The new Ophir Ophir Corporation, and to Lee Erb of Erbtech Engi- radiometric thermometer appears to provide accurate neering for their helpful comments and suggestions measurements both inside and outside of clouds,The during the course of this research. Fight operations limitations of this probe are that it averages over a dis were supported by the Research Aviation Facility of tancc of about 10 m,it is large and complex,it is ex- NCAR and Colorado International Corporation. We pensive and its complicated calibration required an thank Bob Czys of the Ilinois State Water Survey for use of the 1986 PACE data,and Jack Warner who environmental chamber. The maximum values of the apperent error produced allowed us to piggyback portions of this research on by sensor wetting in the reverse-flow probe were in his feld project and who supported acquisition and good agreement with theoretical predictions. However, testing of the Ophir radiometric thermometer at Unauthenticated | Downloaded 04/14/25 02:58 AMAMUTC UTC UeniheeictedIDownbadd 0W1425Q2-58 494 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VouME7 NCAR. Susan Allen drafted most of the figures. This Lawson,R.P,I988-The measuremeat oftemperature from sn air crft in cloud.Ph.D.disertation.Uaivenity of Wyomina,Lar- work was sponsored in part by Grants ATM-8712227 amie,Wyoming. 336 pp. and ATM-8819676 from the National Science Foun- -.and A R Rcd.1s87 Aitorg ce of sensor wetis ina dation. revere 0ow temperature probe Stuh Sposiun ar Aereor. REFERENCES Obsrvetioe5an 1nnumenaionNcwOrieans,253-256. LeMoee,M.A1980.Oa te diEcultyof meuHine tempeature and humidity in cout Comments oe "Shallo convctiom om Albrecht,B.A,S.K.Cox and W.H.Schuber,1979:Radsometric y261ofGATE:Mesosckarcs^MonWaRe,1081702- Io7. mesrerents of ioclood temperature auctuatioes J Appl Meeor.18,1066-1071. - i9s3: Momcotum transport by a ine of cumulonimbus J. Ausin,P.H.M B.Baker,A.M.Blyth and J.B.Jeten,1985: AZmx05. Sci,40,1815-1834. 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