550 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 16

Test of a GPS Radiosonde in Thunderstorm Electrical Environments

W. D AVID RUST NOAA/ERL/National Severe Storms Laboratory, Norman, Oklahoma

THOMAS C. MARSHALL AND MARIBETH STOLZENBURG Department of Physics and Astronomy, University of Mississippi, University, Mississippi

JAMES FITZGIBBON NOAA/National Weather Service, Field Systems Branch, Sensor Test Section, Sterling, Virginia

(Manuscript received 21 October 1997, in ®nal form 7 July 1998)

ABSTRACT Meteorological radiosondes that use navigation systems to determine winds (and horizontal location) can be susceptible to data loss in thunderstorm environments. This paper reports on tests of a radiosonde that uses the Global Positioning System (GPS) for wind®nding. Tests were made by ¯ying the GPS radiosonde into three thunderstorms on free balloons that also carried an electric ®eld meter and a long-range navigation (loran) radiosonde of a type previously tested. The GPS radiosonde performed without any signi®cant loss of wind or thermodynamic data in in-storm maximum electric ®elds of up to Ϫ104 kV mϪ1. Also, no obvious deleterious effect on radiosonde data was found from the presence of nearby lightning. The radiosonde was further tested in a laboratory-produced electric ®eld in an ambient atmospheric pressure of about 70 kPa, in which the radiosonde functioned normally in a vertical electric ®eld up to 160 kV mϪ1 and in a horizontal electric ®eld up to 100 kV mϪ1, the respective maximum applied. Radiosondes that were sprayed with water to simulate ¯ight in rain performed correctly in an electric ®eld of 135 kV mϪ1Ðthe maximum that could be applied safely. The hy- pothesized reason for the excellent wind®nding performance in high electric ®elds is partly the very short antenna length needed for GPS reception. Other factors, which could not be assessed in this study, may include the inherent low-noise susceptibility of the GPS signals and the processing circuitry. The tests showed that the GPS radiosonde obtains wind data in larger electric ®elds than does the loran radiosonde. It is concluded that GPS radiosondes will acquire wind®nding data in most, if not all, thunderstorm and nonthunderstorm clouds that contain high electric ®elds. The thermodynamic data were also very good in the large electric ®elds.

1. Introduction structure, in situ microphysical measurements, etc. The constraints of ballooning in severe thunderstorms and Since the late 1980s, the National Severe Storms Lab- mesoscale convective systems, along with the need to oratory has operated mobile laboratories with mobile receive radiosonde data as the mobile laboratories are ballooning capabilities (Rust 1989; Rust et al. 1990) in motion, led us to use radiosondes that have their own that evolved from the Cross-Chain loran Atmospheric navigation and wind-®nding capabilities and do not re- Sounding System (CLASS) developed at the National quire radio-tracking antennas. Center for Atmospheric Research (Lally and Morel Our experience had been con®ned to the use of the 1985; Lauritsen et al. 1987; NCAR/ATD 1997). A major CLASS technology, which includes the Vaisala RS80- reason for our interest in mobile ballooning has been 15L radiosonde. Tests by Rust et al. (1990) in and near our desire to obtain soundings near and within severe thunderstorms showed that the wind and position in- thunderstorms and mesoscale convective systems. In ad- formation were usually lost but that the thermodynamic dition, we have wanted to place these measurements in data were usually acquired and of usable to excellent the storm context by comparing balloon-borne instru- quality. [The results of these tests on the thermodynamic ment location with Doppler radar data in terms of storm data are recon®rmed here, but the emphasis of this study is to test wind®nding.] Rust et al. (1990) deduced that the cause of the loran (long-range navigation) data loss Corresponding author address: Dr. W. David Rust, NSSL, 1313 was corona discharge (the electrical breakdown of air) Halley Circle, Norman, OK 73019. from the radiosonde's 2.6-m-long loran antenna in the E-mail: [email protected] high electric ®eld near and within storms. Rust et al.'s

᭧ 1999 American Meteorological Society

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statement regarding GPS performance in high electric ®elds but did not provide any details.] The high fre- quency band that carries GPS data has also been credited with increasing reliability (Saarnimo 1998). Further- more, the digital GPS signals and processing may be less prone to problems even if corona noise enters the circuitry. For nonstormy conditions, comparisons between lo- ran and GPS wind®nding and accuracy evaluations have been reported recently by Jaatinen and PaÈlaÈ (1998), Nash et al. (1998), and Saarnimo (1998). For a baseline comparison of our systems, ¯ights were also made in nonstormy weather conditions to determine if, as found by Jaatinen and PaÈlaÈ (1998), Nash et al. (1998), and Saarnimo (1998), the GPS and loran radiosondes, along with their data processing capabilities, gave similar ther- modynamic and wind pro®les. Note that the tests re- ported here were designed to give rough comparisons, FIG. 1. Balloon-borne instrument train to evaluate the performance of a GPS radiosonde in thunderstorm electric ®elds. A loran radio- not to be precision tests. Since the two radiosondes were sonde with a special short loran antenna designed for use in high positioned vertically within about 2 m, they sampled electric ®elds was also ¯own. A schematic comparison of the two the same volume of atmosphere essentially simulta- navigation receiving antennas for wind®nding is shown to the right. neously as they ascended at approximately 5 m sϪ1. The electric ®eld meter measured the local electric ®eld in the vicinity of the radiosondes. (The ®gure is not drawn to scale.) Some, if not all, of the apparent differences in temporal resolution and variability of the data shown here be- tween the two systems resulted from the different data (1990) research indicates that an unmodi®ed Vaisala processing and recording intervals. Since this test was RS80 loran radiosonde loses its wind®nding data in an not aimed at detailed comparisons of radiosonde per- electric ®eld magnitude |E| of approximately 10 kV mϪ1, formance, no attempt was made to reconcile these. Giv- which is well below the maximum electric ®eld of about en that this test was designed to search for major prob- 75±150 kV mϪ1 typically found inside thunderstorms lems and for total loss of wind®nding in large electric and stratiform regions of mesoscale convective systems ®elds, no attempt was made to research loran versus (e.g., Marshall and Rust 1991; Shepherd et al. 1996). GPS wind®nding. For pro®les in storms, the examples In subsequent tests, it was learned that halving the loran of thermodynamic data are shown to document whether antenna length to 1.3 m and encasing it in a dielectric the pro®les appear plausible: they indicate that the ra- tube consistently extended the wind®nding capability to diosondes were functioning reasonably well in the thun- electric ®eld values of up to 40 kV mϪ1, without ap- derstorms. The primary goals of the tests reported here parently adversely affecting the loran reception. More were to determine if the GPS radiosonde would provide recently, when the straight-wire loran antenna was re- wind®nding in the presence of nearby lightning and in placed with an antenna that had a center-loading coil, high electric ®elds and if the maximum electric ®eld in dielectric foam-encased upper and lower vertical ele- which wind®nding was obtained would be greater than ments, and a total length of approximately 0.6 m (Fig. for the loran system. 1), the radiosonde's performance was improved, so that wind®nding data were obtained in electric ®elds of up 2. Instrumentation to about 100 kV mϪ1, although adequate performance does not always occur in such high ®elds. Since this The GPS radiosonde tested was the Vaisala RS80- type of data loss can also occur in winter storms and 15G. This radiosonde has the same sensor suite as other in electri®ed deep-layer clouds without lightning, the Vaisala RS80 radiosondes. There can be a difference in need to acquire winds is not limited to special research the humicap sensor, which was a type A on the GPS use in thunderstorms: it extends to operations in which radiosondes, and types A and H on the loran radio- the winds through deep layers of clouds are needed. sondes. The differences are minor (Schmidlin 1998) and Based on previous experience, and given that the not important in this study. In lieu of the loran circuitry Global Positioning System (GPS) antenna on a radio- and antenna, the RS80-15G has a codeless, eight-chan- sonde is shorter by a factor of 10 than our custom short nel, digital GPS receiver and antenna. The GPS portion loran antenna, we hypothesized that wind®nding from of the radiosonde measures the satellite carrier Doppler GPS will be more reliable than wind®nding from shifts, and the radiosonde telemeters its GPS informa- CLASS in the high electric ®eld beneath and in thun- tion, along with the thermodynamic data, to a ground derstorms and in other highly electri®ed but nonthun- station. The receiving system used during this test was derstorm clouds. [Kaisti (1995) makes an equivalent the commercially available Vaisala DigiCORA II

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MW15. To improve wind®nding accuracy, errors com- lem was the swinging of the instrument, even in light mon to the receivers in the radiosonde and at the ground wind. In this simple test, the problem was apparently station are removed (Saarnimo 1998). A GPS radio- solved for most of the data collection through the use sonde requires a minimum of four satellites to determine of a small drag parachute. (The manufacturer has sub- the horizontal wind (e.g., Jaatinen and PaÈlaÈ 1998). The sequently modi®ed the line-release system for a smooth- GPS radiosonde data shown here were taken in the sys- er release and doubled the line length that attaches the tem's research mode, which recorded thermodynamic GPS radiosonde to the balloon to 60 m. The longer train and wind®nding data every 2 s. The GPS wind®nding reduces the pendulum effect experienced by the radio- data were calculated every 0.5 s and were ®ltered to sonde.) give 2-s raw data points (Kaisti 1995). The data from The tests also included wind®nding by tracking the CLASS are a point every 10 s. Each thermodynamic balloon with dual, optical theodolites. The theodolite data point is calculated from a linear least squares data were intended to provide an independent, albeit smoothing of raw data obtained every 1.5 s. Each 10- coarse, check on the radiosondes' wind®nding in clear s wind®nding data point is calculated from 60 s of loran air. They were not intended to be precise enough to serve information (Lauritsen et al. 1987; NCAR/ATD 1997). as highly accurate ground truth. Winds from the dual- Pertinent to the behavior of the RS80-15G in a large theodolite data track the radiosonde data in both wind electric ®eld is the packaging of the radiosonde. The speed and direction (Fig. 2). In the example shown in circuit cards, water-activated battery, and GPS receiving Fig. 2, the theodolite data have at 625 s (at a P ഠ 468 antenna are housed in a Styrofoam case. This dielectric mb and z ഠ 6.4 km) one obvious outlier in wind di- housing not only holds the components but also inhibits rection and a few possible outliers in wind speed. The corona. Surrounding most of the Styrofoam is a water- spikes in the temperature data from the loran radiosonde repellent, thick-paper type of outer packaging that has are from a few isolated points with high noise. Other four, 1.5-cm-diameter metal grommets at the top to hold comparison ¯ights in fair-weather conditions yielded instrument rigging lines. The 400-MHz transmitting an- similar levels of agreement. tenna protrudes vertically from the bottom of the ra- Three ¯ight tests were made in thunderstorms. In all diosonde. The antenna is made of copper wire. It is 16 three in-storm ¯ights, the balloon burst at unusually low cm long and 1.5 mm in diameter and is sheathed with altitudes, most likely because of hail. Even with the a thin dielectric except at its tip. The transmitting an- premature end to the soundings, the ¯ight test data are tenna tip was straight, which is a worst-case con®gu- useful because they provide a measure of GPS radio- ration. (We had con®rmed in our previous tests that if sonde wind®nding performance inside thunderstorms the antenna tip is tightly curled, the corona-onset ®eld and in proximity to lightning. The lightning was veri®ed is larger.) to be nearby via observers' reports of thunder, an in- As with earlier testing of loran radiosonde perfor- terferometric lightning mapping system that was being mance during in-storm ¯ights (Rust et al. 1990), an operated by New Mexico Institute of Mining and Tech- electric ®eld meter was ¯own on the same balloon-borne nology, and the ground ®eld mills around Langmuir instrument train (Fig. 1) to provide a quantitative mea- Laboratory. These storm soundings are shown versus sure of the electric ®eld in which the radiosondes were altitude, as is typically done to place such data in the embedded. The electric ®eld meter and procedures for storm context. analysis of the electric ®eld data have been described A thunderstorm ¯ight was launched at 1941 UTC 3 in several papers (e.g., Marshall et al. 1995). Both a August 1996 (Fig. 3). Two storm cells were over the GPS and a loran radiosonde were ¯own on each thun- area, with the most active regions of lightning appar- derstorm ¯ight reported here. Because it is discussed ently within about 5 km. The two cells produced about later in this paper, note that the electric ®eld meter pro- 30 ¯ashes during the balloon ascent to 7 km. The electric vides substantial drag: the instrument train quickly sta- ®eld meter data were noisy and unusable from about bilizes after launch, and the radiosondes do not swing 4.4 to 4.9 km and above 6.2 km because of a problem much. in the telemetry-receiving hardware at the ground, which was later corrected. The ®rst 19 2-s data points from the GPS radiosonde were discarded. At ®rst glance, 3. Balloon-borne ¯ight tests these initial data appear valid. However, between 32 and All the tests were conducted in New Mexico at the 38 s into the ¯ight, the pressure stays constant at 679 Irving Langmuir Laboratory for Atmospheric Research, mb (ഠ3.4 km). Then the pressure data repeat values which is located on a mountain ridge at 3.2 km MSL. from within the range of values recorded during the ®rst As part of the fair-weather ¯ights made with a GPS and 38 s. The temperature recorded in the ®rst 38 s appears a loran radiosonde on the same balloon, we investigated to be too warm in comparison with the subsequent data reports that the GPS radiosonde sometimes lost wind- and the data from the other radiosonde, which indicate ®nding data immediately after a launch. For the 1996 a normal ascent. Thus, the GPS radiosonde data points version of the RS80-15G radiosonde and its line-re- in these 38 s may be an artifact of the processing or leasing apparatus, we quickly concluded that the prob- recording. After the ®rst 38 s, the data are well behaved,

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FIG. 2. Wind®nding from optical tracking of balloon, wind, and thermodynamic data from GPS and loran radiosondes ¯own on the same balloon in fair-weather conditions. The ¯ight was from the Irving Langmuir Laboratory for Atmospheric Research (3.2 km MSL) at 2259 UTC 5 Aug 1996. The data are the smoothed 10-s-interval values for the loran radiosonde and the 2-s-interval values for the GPS radiosonde. The spikes in the loran radiosonde temperature data are from averages with large errors. (The two temperature curves are the lowest two in the bottom panel.) The average ascent rate calculated by CLASS is about 5 m sϪ1.

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FIG. 3. Thunderstorm soundings of wind speed, wind direction, and temperature from GPS and loran radiosondes on the same balloon and the electric ®eld E with temperature T and relative humidity RH from the GPS radiosonde. The balloon was launched from the Irving Langmuir Laboratory for Atmospheric Research (3.2 km MSL) at 1941 UTC 3 Aug 1996. The ascent sounding ended at approximately 7 km because the balloon burst. A large ®eld change of lightning is denoted by L. Visually observed entry into the cloud by the balloon- borne instruments is shown. The RH could exceed 100% in the research data mode of the GPS radiosonde data processor.

Unauthenticated | Downloaded 09/26/21 09:12 AM UTC MAY 1999 RUST ET AL. 555 the temperature plot follows that from the other radio- curs when the loran wind®nding data had a sudden in- sonde, and all possible 2-s thermodynamic data from crease in the error in the 10-s averaged data. Thus, the the GPS radiosonde were obtained. We did not see this loran wind®nding data appear to be incorrect, but this problem in any other ¯ights: its cause remains unknown cannot be determined conclusively. There were no ob- but appears unrelated to the weather. vious outliers in the thermodynamic data from either The outliers in thermodynamic data from the loran radiosonde. radiosonde are of interest in this ¯ight. Of the real-time processed 10-s data points, about 12% are scattered in 4. Tests in laboratory-produced high electric ®elds the data as outliers. In contrast, an examination of the raw 1.5-s data shows that less than 3% of the individual A controllable electric ®eld that simulated the interior data points appear to be outliers. Of all the test ¯ights of a highly electri®ed cloud was created in a parallel- and laboratory tests, this ¯ight contains the largest per- plate capacitor connected to a direct-current high-volt- cent of thermodynamic data outliers. Even so, the qual- age supply (Fig. 6). An advantage of such laboratory ity of the overall thermodynamic data is quite high. tests is the ability to place the radiosonde in a large The GPS radiosonde had ®ve satellites at launch, but electric ®eld that can be sustained, repeated, etc. The no other satellite count was logged. (The number of parallel-plate system was embedded in ambient, moun- satellites was not recorded by the system software. In taintop air in the balloon hangar at Langmuir Laboratory addition, because of other duties during storm ¯ights, where the atmospheric pressure was typically about 70 the operator made only intermittent comments in the log kPa. A GPS repeater transmitter was used to obtain the regarding the number of satellites.) There were three GPS satellite signals inside the metal hangar and be- short gaps in the wind®nding data during a 50-s period tween the parallel plates. Known voltages were applied between approximately 5.38 and 5.64 km. The maxi- to the upper plate, which was about 1 m above the lower mum electric ®eld recorded during this ¯ight was about plate. (The measured separation was 0.93 m in the center 40 kV mϪ1, which occurred at about 6.1 km. One close of the plates and 0.96 m at the edges.) A negative voltage and large lightning-caused ®eld change is seen at 5.45 was applied to the upper plate and created a positive km. The ®rst dropout in wind®nding occurred about 20 electric ®eld whose magnitude was simply the applied s before the lightning. Very little wind®nding data were voltage divided by the plate separation. While the elec- lost. Figure 3 also shows pro®les of wind speed, wind tric ®eld for corona onset will vary slightly for positive direction, and temperature from the GPS and loran ra- and negative polarities, the results from a single-polarity diosondes for this ¯ight. The pro®les are similar. Again, test will provide the approximate values for corona onset this rough comparison is not meant to compare absolute and, more importantly, the approximate electric ®eld for accuracies but to show that the radiosondes performed any failure in the radiosonde system. As the electric in a reasonable way inside the storm. ®eld was increased, the data reception from the radio- The second ¯ight on 3 August 1996 was launched at sonde through its telemetry link to its ground receiving 2034 UTC (Fig. 4). The sounding has several large ®eld station was monitored for loss of either thermodynamic changes from lightning, which coincided with obser- data or GPS wind®nding data. In addition, the number vations by the lightning mapping system and other ob- of GPS satellites received was frequently logged by an servations. All possible GPS wind®nding data were ob- observer. tained during the ¯ight. The GPS radiosonde had ®ve The ®rst test was made in daylight, and corona, which to seven satellites during the ascent. The maximum elec- is dimly luminous, could not be observed visually. The tric ®eld was about 38 kV mϪ1. Figure 4 also shows radiosonde was initially dry and was suspended in am- pro®les of wind speed, wind direction, and temperature bient air whose relative humidity, measured by the ra- from the GPS and loran radiosondes. There are no ob- diosonde, was about 50%. The electric ®eld was in- vious outliers in the thermodynamic data from either creased slowly, and audible corona was heard at an E radiosonde. ഠ 60 kV mϪ1. The radiosonde was receiving three sat- The third test ¯ight into a thunderstorm was at 2249 ellites and acquired the needed fourth for winds as the UTC 7 August 1996 (Fig. 5). Although the balloon electric ®eld reached 112 kV mϪ1 (Fig. 7). The electric achieved little altitude before it burst, the maximum ®eld was increased further to approximately 160 kV electric ®eld was Ϫ104 kV mϪ1. During this sounding, mϪ1, and the system continued to receive and process at least one ¯ash occurred (at about the time the balloon four GPS satellites for wind®nding. Then the voltage entered the cloud), but no lightning-caused ®eld changes was turned down to zero very rapidly to produce a large are obvious in the electric ®eld pro®le. The ®rst 6 s of ®eld change that simulated nearby lightning. No detri- GPS wind®nding data are missing, after which four or mental effect on wind or thermodynamic data was de- ®ve GPS satellites were received, and all possible winds tected from the large ®eld change. The test continued from the GPS radiosonde were calculated for the ascent. after the radiosonde had been sprayed with water. Au- Figure 5 also shows pro®les of wind speed, wind di- dible corona began at 40 kV mϪ1. As the electric ®eld rection, and temperature from the GPS and loran radio- was increased to 100 kV mϪ1, there were short periods sondes. The substantial disagreement in the winds oc- when the number of satellites dropped from four to

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FIG. 4. Thunderstorm soundings of wind speed, wind direction, and temperature from GPS and loran radiosondes on the same balloon and the electric ®eld E with temperature T and relative humidity RH from the GPS radiosonde. The balloon was launched from the Irving Langmuir Laboratory for Atmospheric Research (3.2 km MSL) at 2034 UTC 3 Aug 1996. The sounding ended at 4.5 km, probably because hail burst the balloon. The occurrence of lightning is denoted by L. Visually observed entry into the cloud by the balloon-borne instruments is shown.

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FIG. 5. Thunderstorm soundings of wind speed, wind direction, and temperature from GPS and loran radiosondes on the same balloon and the electric ®eld E with temperature T and relative humidity RH from the GPS radiosonde. The balloon was launched from the Irving Langmuir Laboratory for Atmospheric Research (3.2 km MSL) at 2249 UTC 7 Aug 1996. The sounding ended at 4.2 km, probably because hail burst the balloon. Visually observed entry into the cloud by the balloon-borne instruments is shown. The RH could exceed 100% in the research data mode of the GPS radiosonde data processor. The arrows point to where the loran wind data started and continued to have larger errors.

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FIG. 6. Parallel-plate capacitor and high-voltage supply to generate electric ®elds to test GPS radiosonde performance. The radiosonde is shown suspended vertically between the plates. The concentration of the electric ®eld lines on the radiosonde is indicated in a non- quantitative manner. A nearby repeater antenna (not shown) beamed GPS satellite transmissions directly between the parallel plates. three. The dropouts of wind (at three satellites) can be seen in Fig. 7. When four satellites were received, the radiosonde continued to perform correctly in an electric ®eld up to 100 kV mϪ1. There were some lags of a few tens of seconds between changes in the number of sat- ellites and the loss or gain of wind data. Whether these delays were real or from possible delays in entering the observer's comments in the data log is unknown, but the differences in time are small. The test was repeated (at 1900±2100 s in Fig. 7), with the radiosonde sus- FIG. 8. Time exposure of corona from a GPS radiosonde. The pended horizontally in the plate capacitor to analyze the ellipses of light were caused by slow rotation and swaying of the effect of a horizontal electric ®eld. Five satellites were radiosonde. A photographic ¯ash unit was used to obtain the general received, and all data were received with no dropouts outline of the radiosonde to help identify the corona sites. The corona at the top was apparently off the temperature and humidity element support, while at the bottom, the corona was from the tip of the 400- MHz transmitting antenna. (Photograph by and used with the per- mission of C. Andrew Niesen.)

in an electric ®eld up to 100 kV mϪ1. Also, the wind speed data were always 0.0 m sϪ1 during the entire test, indicating good data accuracy in high electric ®elds. There were no obvious outliers in the thermodynamic data during this test. Testing was also performed in very dark conditions at night to allow observers to seeÐand a low-light-level video camera to recordÐthe luminosity of corona from the radiosonde. Figure 8 is a time-exposure photograph of corona from the radiosonde during one such test. The ellipses of light con®rm that corona occurred from the temperature and humidity element that extends upward and outward from near the top of the radiosonde. They FIG. 7. Performance of wind®nding by GPS in laboratory-produced also con®rm that corona occurred from the 400-MHz electric ®eld E. Zero time is the start of the test at 1624 UTC 6 Aug radiosonde-transmitting antenna that extends downward 1996. The radiosonde was initially dry and suspended in its normal vertical ¯ying orientation in the vertical electric ®eld. The radiosonde from the radiosonde as it rotated slowly and swayed in was then sprayed with water (at ഠ1000 s), and the test was repeated. the electric ®eld. During this test, the mountaintop and From 1900 to 2100 s, the still damp radiosonde was suspended hor- test facility were in cloudy air much of the time, with izontally to test the effects of a horizontal electric ®eld. Since the a radiosonde-measured humidity of approximately 90% radiosonde was being recon®gured, data are not shown from about 1250 to 1900 s; the test ended at 2100 s. When wind®nding data and a temperature of about 9ЊC. The radiosonde was were available, the wind speed and direction from the stationary hung vertically. Audible corona began at an E ഠ 40 kV radiosonde were consistently zero. mϪ1, with corona from the radiosonde visible at about

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in thunderstorms, we ®nd little evidence that GPS wind- ®nding data are adversely affected by either a high elec- tric ®eld or the presence of nearby lightning. These ¯ight results are corroborated and enhanced by the ®ndings in larger laboratory-produced electric ®elds. The max- imum laboratory-produced electric ®eld in this test of 160 kV mϪ1 is greater than many thunderstorm electric ®elds reported in the literature. The number of GPS satellites obtained by the radiosonde during ¯ights changed, but in a manner not obviously connected with the electric ®eld or the occurrence of lightning. Fur- thermore, the maximum number of satellites in any giv- en laboratory test was often received during the max- imum electric ®eld, suggesting no adverse effect from a large electric ®eld. We think that the variations in the number of satellites received were due primarily to changing satellite reception. FIG. 9. Performance of wind®nding by GPS in laboratory-produced electric ®eld E. Zero time is the start of the test at 0305 UTC 9 Aug The comparison of these tests with previous ones on 1996. The second part of the test was with the radiosonde very wet. loran radiosondes indicates that the GPS radiosondes In both parts of the test, the radiosonde was suspended in its normal are more reliable in obtaining winds (and horizontal vertical ¯ying orientation in the vertical electric ®eld. Since the ra- location) in highly electri®ed clouds and in the vicinity diosonde was being recon®gured, data are not shown from about 750 to 1370 s: the test ended at 1750 s. When wind®nding data were of lightning than are radiosondes using loran. These available, the wind speed and direction from the stationary radiosonde results from thunderstorms and laboratory-produced were consistently zero. electric ®elds are also applicable to nonthunderstorm, electri®ed clouds such as nimbostratus clouds, winter storms without lightning, etc. We had only a single man- 60 kV mϪ1. The system initially received wind data to ufacturer's radiosonde system and GPS radiosondes an E ഠ 135 kV mϪ1 (Fig. 9) except for a 6-s dropout available for testing, but we expect similar wind®nding at 700 s. Within a few more kilovolts per meter, the performance of all GPS radiosondes. The reason for satellite reception dropped to three, and wind data were their improved reliability is at least in part simply that lost. This event is the only occurrence that suggests a the much shorter GPS antenna compared to a loran an- possible link between a high electric ®eld and the loss tenna increases the electric ®eld needed to produce co- of wind data. However, the event could not be repro- rona from the navigation receiving antenna. However, duced in subsequent parts of this test, indicating that the test data showed good performance even in the pres- something else caused the wind data loss. For example, ence of corona from the radiosonde. Other factors in the number of satellites sometimes changed during tests, the excellent performance, which were not evaluated, even in fair weather. This was also observed with an may include the frequency band of GPS, inherent low independent, portable GPS receiver outside the hangar noise susceptibility of the GPS signals, and the pro- on the mountain ridge. cessing circuitry. We believe the important conclusion The high voltage was turned off, the radiosonde was is that GPS radiosondes will acquire wind®nding data sprayed with water, and the test was repeated. Corona in most, if not all, thunderstorms and clouds that contain was observed and recorded from the top and bottom of large electric ®elds. the radiosonde and from the 400-MHz transmitting an- tenna. The test was terminated at an E ഠ 135 kV mϪ1 Acknowledgments. We thank Dennis Nealson and because of concern that the observed sparking might Paul Grif®n for help with sounding system maintenance, lead to a full arc across the parallel-plate gap and dam- and Les Showell for assistance in data collection. We age to the high-voltage power supply. The radiosonde thank Patrick Stoller and Ivy Winger for their assistance received ®ve GPS satellites and all possible data. Corona in data collection and processing: 80% of their partic- and small sparks did not appear to affect the radio- ipation was funded through a National Science Foun- sonde's thermodynamic and wind®nding data. There dation Research Experience for Undergraduates grant, were no obvious outliers in the thermodynamic data NSF ATM-9508621, and 20% through grant NSF ATM- during this test. 9403664. We thank Bill Winn for providing logistical support and making the Irving Langmuir Laboratory for Atmospheric Research available for this test, Mark Stan- 5. Conclusions ley and Paul Krehbiel for the video of corona and the The thermodynamic data were found to be of usable observations of lightning with the New Mexico Institute to excellent quality in all ¯ights and tests in high electric of Mining and Technology interferometric lightning ®elds and nearby lightning. From three balloon ¯ights mapping system, and C. Andrew Niesen for the pho-

Unauthenticated | Downloaded 09/26/21 09:12 AM UTC 560 JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY VOLUME 16 tograph of corona from the radiosonde. We thank Rich Marshall, T. C., and W. D. Rust, 1991: Electric ®eld soundings through Thomas for making this test possible by providing the thunderstorms. J. Geophys. Res., 96, 22 297±22 306. , W. Rison, W. D. Rust, M. Stolzenburg, J. C. Willett, and W. radiosondes and the National Weather Service sounding P. Winn, 1995: Rocket and balloon observations of electric ®eld system. in two thunderstorms. J. Geophys. Res., 100, 20 815±20 828. Disclaimer: Reference in this paper to any speci®c Nash, J., J. B. Elms, J. Stancombe, R. Smout, and D. Lyth, 1998: commercial product or manufacturer does not constitute Operational implementation of GPS wind®nding test results from or imply its endorsement, recommendation, or favoring the UK and the South Atlantic. Proc. 10th Symp. on Meteoro- logical Observations and Instrumentation, Pheonix, AZ, Amer. by the United States Government. Meteor. Soc., 58±63. NCAR/ATD, cited 1997: SSSF observing facilities description and speci®cations. [Available online at http://www.atd.ucar.edu/sssf/ REFERENCES facilities/sssf࿞facility࿞descrip/sssf.html.] Jaatinen, J., and E. PaÈlaÈ, 1998: On the wind®nding accuracy of ter- Rust, W. D., 1989: Utilization of a mobile laboratory for storm elec- restrial NAVAIDS. Proc. 10th Symp. on Meteorological Obser- tricity measurements. J. Geophys. Res., 94, 13 305±13 311. vations and Instrumentation, Phoenix, AZ, Amer. Meteor. Soc., , R. Davies-Jones, D. W. Burgess, R. A. Maddox, L. C. Showell, 45±50. T. C. Marshall, and D. K. Lauritsen, 1990: Testing a mobile Kaisti, K., 1995: New low-cost GPS-solution for upper-air wind ®nd- version of a cross-chain LORAN atmospheric sounding system ing. Proc. Ninth Symp. on Meteorological Observations and In- (M-CLASS). Bull. Amer. Meteor. Soc., 71, 173±180. strumentation, Charlotte, NC, Amer. Meteor. Soc., 16±20. Saarnimo, T., 1998: GPS the global wind®nding method. Proc. 10th Lally, V. E., and C. Morel, 1985: Wind measurements using all avail- Symp. on Meteorological Observation and Instrumentation, able LORAN stations. Proc. 14th Annual Technical Symp. of the Phoenix, AZ, Amer. Meteor. Soc., 51±54. Wild Goose Association, Santa Barbara, CA, Wild Goose As- Schmidlin, F. J., 1998: Radiosonde relative humidity sensor perfor- sociation, 84±95. mance: The WMO intercomparisonÐSept 1995. Proc. 10th Lauritsen, D., Z. Malekmadani, C. Morel, and R. Macbeth, 1987: Symp. on Meteorological Observation and Instrumentation, The Cross-chain LORAN Atmospheric Sounding System Pheonix, AZ, Amer. Meteor. Soc., 68±71. (CLASS). Preprints, Sixth Symp. on Meteorological Observa- Shepherd, T. R., W. D. Rust, and T. C. Marshall, 1996: Electric ®elds tions and Instrumentation, New Orleans, LA, Amer. Meteor. and charges near 0ЊC in stratiform clouds. Mon. Wea. Rev., 124, Soc., 340±343. 919±938.

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