Showing papers on "Thunderstorm published in 1999"
01 Jun 1999
TL;DR: The Lightning Imaging Sensor (LIS) is a NASA Earth Observing System (EOS) instrument on the Tropical Rainfall Measuring Mission (TRMM) platform designed to acquire and investigate the distribution and variability of total lightning (i.e., cloud-to-ground and intracloud) between q35' in latitude.
Abstract: The Lightning Imaging Sensor (LIS) is a NASA Earth Observing System (EOS) instrument on the Tropical Rainfall Measuring Mission (TRMM) platform designed to acquire and investigate the distribution and variability of total lightning (i.e., cloud-to-ground and intracloud) between q35' in latitude. Since lightning is one of the responses of the atmosphere to thermodynamic and dynamic forcing, the LIS data is being used to detect deep convection without land-ocean bias, estimate the precipitation mass in the mixed phased region of thunderclouds, and differentiate storms with strong updrafts from those with weak vertical motion.
250 citations
TL;DR: In this paper, a distinct class of short-duration electric field change emissions was identified and characterized, termed narrow positive bipolar pulses (NPBPs), emitted from singular intracloud discharges that occurred in the most active regions of three thunderstorms located in New Mexico and west Texas.
Abstract: Observations of radio emissions from thunderstorms were made during the summer of 1996 using two arrays of sensors located in northern New Mexico. The first array consisted of three fast electric field change meters separated by distances of 30 to 230 km. The second array consisted of three broadband (3 to 30 MHz) HF data acquisition systems separated by distances of 6 to 13 km. Differences in signal times of arrival at multiple stations were used to locate the sources of received signals. Relative times of arrival of signal reflections from the ionosphere and Earth were used to determine source heights. A distinct class of short-duration electric field change emissions was identified and characterized. The emissions have previously been termed narrow positive bipolar pulses (NPBPs). NPBPs were emitted from singular intracloud discharges that occurred in the most active regions of three thunderstorms located in New Mexico and west Texas. The discharges occurred at altitudes between 8 and 11 km above mean sea level. NEXRAD radar images show that the NPBP sources were located in close proximity to high reflectivity storm cores where reflectivity values were in excess of 40 dBZ. NPBP electric field change waveforms were isolated, bipolar, initially positive pulses with peak amplitudes comparable to those of return stroke field change waveforms. The mean FWHM (full width at half maximum) of initial NPBP field change pulses was 4.7 μs. The HF emissions associated with NPBPs were broadband noise-like radiation bursts with a mean duration of 2.8 μs and amplitudes 10 times larger than emissions from typical intracloud and cloud-to-ground lightning processes. Calculations indicate that the events represent a distinct class of singular, isolated lightning discharges that have limited spatial extents of 300 to 1000 m and occur in high electric field regions. The unique radio emissions produced by these discharges, in combination with their unprecedented physical characteristics, clearly distinguish the events from other types of previously observed thunderstorm electrical processes.
240 citations
TL;DR: In this article, a discriminant analysis was performed on coincident upper-air sounding data from Spokane, Washington, to classify convective days as either "dry" or "wet" for several stations in the Pacific Northwest.
Abstract: Lightning is the primary cause of fire in the forested regions of the Pacific Northwest, especially when it occurs without significant precipitation at the surface. Using thunderstorm occurrence and precipitation observations for the period 1948‐77, along with automated lightning strike data for the period 1986‐96, it was possible to classify convective days as either ‘‘dry’’ or ‘‘wet’’ for several stations in the Pacific Northwest. Based on the classification, a discriminant analysis was performed on coincident upper-air sounding data from Spokane, Washington. It was found that a discriminant rule using the dewpoint depression at 85 kPa and the temperature difference between 85 and 50 kPa was able to classify correctly between 56% and 80% of the convective days as dry or wet. Also, composite maps of upper-air data showed distinctly different synoptic patterns among dry days, wet days, and all days. These findings potentially can be used by resource managers to gain a greater understanding of the atmospheric conditions that are conducive to lightning-induced fires in the Pacific Northwest.
190 citations
TL;DR: In this article, the discovery of the optical phenomena now termed "red sprites" along with the properties that have been experimentally determined are discussed, along with areas of disagreement between experimentalists are pointed out.
Abstract: In the last decade there has been a great deal of interest in the detection and understanding of phenomena occurring above active thunderstorms. The discovery of the optical phenomena now termed “red sprites” is discussed, along with the properties that have been experimentally determined. Areas of disagreement between experimentalists are pointed out. Other optical and electromagnetic phenomena associated with red sprites are presented. These include blue jets, transionospheric pulse pairs, and gamma ray flashes. Particular attention is given to the work on perturbations on very low frequency radio wave transmissions (“VLF sprites”), which has provided estimates of the electrical properties of sprites. Research into activity above thunderstorms will continue to lead to a greater understanding of the coupling between thunderstorms in the troposphere to the stratosphere, mesosphere, ionosphere, and beyond.
166 citations
TL;DR: In this paper, the Fly's Eye photometric array was used to identify the cause of lightening electromagnetic pulses (EMP) in the lower ionosphere of a thunderstorm over Mexico recorded at Langmuir Laboratory.
Abstract: Optical flashes in the lower ionosphere due to the transient heating caused by lightning electromagnetic pulses (EMP) are unambiguously identified with the Fly's Eye photometric array. Data from a thunderstorm over Mexico recorded at Langmuir Laboratory on August 27 1997 demonstrate that relatively common negative cloud-to-ground lightning is a previously unrecognized major cause of elves. The spatial extent of the transient heating is shown optically to be typically at least 200–700 km laterally, indicating the possibility for accumulation of ionization effects produced by successive flashes within large nighttime thunderstorm systems. One especially bright event suggests that temporal fine-structure in the causative very low frequency EMP can manifest itself in the photometric record of elves.
119 citations
TL;DR: The mean annual flash density, thunderstorm duration, and flash rates were calculated using 121.7 million cloud-to-ground lightning flashes in the continental United States for the period 1989-96 as discussed by the authors.
Abstract: The mean annual flash density, thunderstorm duration, and flash rates were calculated using 121.7 million cloud-to-ground lightning flashes in the continental United States for the period 1989–96. Florida had flash densities over 11 flashes km−2 yr−1, while the Midwest, Oklahoma, Texas, and the Gulf Coast had densities greater than 7 flashes km−2 yr−1. There was a relative minimum in flash density (three flashes km−2 yr−1) in the Appalachian Mountains and Missouri. Thunderstorm duration values exceeded 120 h yr−1 in Florida and 105 h yr−1 in New Mexico, Arizona, and the Gulf Coast. The maximum annual flash rates exceeded 45 flashes h−1 in the Midwest, along the Florida coasts, and along the mid-Atlantic coast with the minimum flash rates, 15 flashes h−1, over the Appalachian and Rocky Mountains. The relationship between thunderstorm duration and flash density is Flash_Density = 0.024(Flash_Hours)1.29 producing expected flash densities that are within 30% of the measured densities for over 70% of ...
117 citations
TL;DR: In this article, the temporal progression of tropical convective systems and the mean atmospheric state in their vicinity are constructed from a time series of geostationary satellite and operational raw-insonde data.
Abstract: Using a compositing technique, the temporal progression of tropical convective systems and the mean atmospheric state in their vicinity is constructed from a time series of geostationary satellite and operational rawinsonde data. The technique establishes the stage in the life cycle of convection prevailing at a given place and time, by a simple objective method using time series of satellite brightness temperature (Tb) histograms collected from a region surrounding the site. Soundings are classified according to their placement in the convective life cycle, and composites formed that represent the areal-mean state of the convecting atmosphere at each stage, for several scales of horizontal averaging. The temporal structure found here for the mesoscale-mean atmosphere closely resembles existing observations of the horizontal structure of a tropical squall line, albeit with certain reductions in amplitude and stabilization rate. This supports the generality of previous findings that the physical m...
110 citations
TL;DR: In this paper, a versatile workstation version of the NCEP Eta Model is used to simulate three excessive precipitation episodes in the central United States, including 16−17 June 1996 in the upper Midwest, 17 July 1996 in western Iowa and 27 May 1997 in Texas.
Abstract: A versatile workstation version of the NCEP Eta Model is used to simulate three excessive precipitation episodes in the central United States. These events all resulted in damaging flash flooding and include 16‐17 June 1996 in the upper Midwest, 17 July 1996 in western Iowa, and 27 May 1997 in Texas. The episodes reflect a wide range of meteorological situations: (i) a warm core cyclone in June 1996 generated a meso-b-scale region of excessive rainfall from echo training in its warm sector while producing excessive overrunning rainfall to the north of its warm front, (ii) a mesoscale convective complex in July 1996 produced excessive rainfall, and (iii) tornadic thunderstorms in May 1997 resulted in small-scale excessive rains. Model sensitivity to horizontal resolution is investigated using a range of horizontal resolutions comparable to those used in operational and quasi-operational forecasting models. Sensitivity tests are also performed using both the Betts‐Miller‐Janjic convective scheme (operational at NCEP in 1998) and the Kain‐Fritsch scheme. Variations in predicted peak precipitation as resolution is refined are found to be highly case dependent, suggesting forecaster interpretation of increasingly higher resolution model quantitative precipitation forecast (QPF) information will not be straightforward. In addition, precipitation forecasts and QPF response to changing resolution are both found to vary significantly with choice of convective parameterization.
105 citations
TL;DR: In this article, the authors examined the operational potential for predicting the onset of cloud-to-ground lightning in 39 airmass thunderstorms that developed over the NASA Kennedy Space Center, Florida, to determine the best lightning initiation signature.
Abstract: The operational potential for predicting the onset of cloud-to-ground lightning is examined. WSR-88D reflectivity echoes were analyzed for 39 airmass thunderstorms that developed over the NASA Kennedy Space Center, Florida, to determine the best lightning initiation signature. This study examined thunderstorms in the months of May–September 1992–97. These storms were studied in conjunction with cloud-to-ground (CG) lightning flash locations from the National Lightning Detection Network. From a time series of radar echoes, it was found that the 40-dBZ echo detected at the −10°C temperature height is the best indicator for predicting the beginning of CG lightning activity. The observed median lag time, or warning time, between this lightning initiation signature and the first CG lightning flashes was 7.5 min. Other lightning initiation signatures examined at −15° and −20°C temperature heights yielded shorter warning times.
103 citations
TL;DR: In this article, the results of monthly latitudinal (8°-30° N) and latitude belts averaged seasonal thunderstorm activity over India by using monthly data from a large number of Indian stations from 1970 to 1980.
Abstract: This paper describes the results of monthly latitudinal (8°-30° N) and latitude belts (8°-10°, 10°-15°, 15°-20°, 20°-25°, and 25°-30°N) averaged seasonal thunderstorm activity over India by using monthly data from a large number of Indian stations from 1970 to 1980. The latitudinal variation in the premonsoon (March-April-May) and monsoon season (June-September) months is described and the results are discussed. An examination of the seasonal thunderstorm day activity in the first four belts indicated systematic changes in their signals of semiannual oscillation. These changes are noted to be a function of latitude and season and appear to be consistent with the seasonal migration of the Intertropical Convergence Zone and solar heating of the Indian landmass. We compare the thunderstorm day activity with the monthly mean maximum values of the surface wet-bulb (Tw) temperatures in the five latitude belts over the Indian region. By using rainfall data for the same period of study, the relationship between seasonal rainfall and number of thunderstorm days over the 11 year period is examined. The results of variation of the ratio of monthly rainfall to thunderstorm days (RTR) during different phases of the southwest monsoon are also presented. Results of the monthly mean electrical conditions of mesoscale and isolated deep convective storms at Pune are summarized. It is noted that the electrification of the premonsoon season thunderstorms dominated by a factor of 3-4 over the monsoon ones. We have examined at length the possible influence of the El Nino on the occurrence and electrification of thunderstorms over the Indian region.
93 citations
TL;DR: In this article, the authors investigated the role of gravity current and bore development at surface cold fronts in the generation of severe frontal convection and found that the bore developed after a nocturnal inversion, which acted as a waveguide, had become established.
Abstract: This case study addresses the issue of gravity current and bore development at surface cold fronts, and the role of these phenomena in the generation of severe frontal convection. The event investigated occurred on 27 April 1991 during the Cooperative Oklahoma Profiler Studies 1991 field project. The development of a bore from a gravity current–like structure along a cold front, the subsequent propagation of the bore ahead of the front on a low-level inversion, and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations. Evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory. The bore developed after a nocturnal inversion, which acted as a waveguide, had become established. The bore and gravity current were both evident as “fine lines” in the radar reflectivity displays. A microscale envelope of enhanced water vapor with an embedded roll cl...
TL;DR: In this paper, a co-located measurements of ambient, electrostatic-field profiles and rocket-triggered lightning phenomenology under Florida thunderstorms are reported and the conditions that are sufficient to initiate and sustain the propagation of positive lightning leaders are identified.
TL;DR: The Working Group on Storms as mentioned in this paper considered tropical cyclones, extratropical cyclones and their associated winds and effects other than on temperatures and precipitation (which are dealt with by the other working groups) to be in their purview.
Abstract: The Working Group on Storms considered tropical cyclones, extratropical cyclones, thunderstorms and their associated winds and effects other than on temperatures and precipitation (which are dealt with by the other working groups) to be in their purview. Changes in observing systems and distribution of observers and people impacted by these phenomena confound trend analysis. In light of the difficulty of assembling homogeneous time series of small-scale phenomena such as thunderstorms, tornadoes and hail, and also the problems in wind measurements, the working group recommends that indices of wind be developed by taking advantage of long surface (r. sea-level) pressure measurements and analyses. Because wind is a vector, two pairs of readings that are orthogonal are desirable. Instantaneous values over about 1000 km scales are desirable to generate statistics relevant to wind extremes. Recommendations are given on how the data might profitably be processed. Several other recommendations are made concerning data acquisition and processing, some of which apply to reanalysis of past data and some apply to future processing of data. Various “extremes indices” are also suggested.
TL;DR: In this article, 30 years of rainfall data collected from a dense rain gage network on the 334 km2 Little River Watershed near Tifton, Georgia, were analyzed for this purpose.
Abstract: The Georgia Coastal Plain of the United States holds significant agricultural and hydrologic importance. The
profitability and sustainability of agriculture in this and other regions are dependent upon climatic patterns and, in
particular, rainfall. The temporal and spatial variability of this rainfall play key roles in agricultural management.
Developing an understanding of seasonal patterns and individual storm characteristics is critical. Thirty years of rainfall
data collected from a dense rain gage network on the 334 km2 Little River Watershed near Tifton, Georgia, were analyzed
for this purpose. Storm patterns were characterized by season to establish means and trends. Individual storm
characteristics and spatial correlation patterns within storms were quantified. Rainfall patterns, although highly variable
from year to year, show rainfall to be greatest in the midsummer months with high intensity, convective thunderstorms.
While these summer storms yield relatively low rainfall depths, they occur more frequently than during other seasons.
Frontal storms with moderate rainfall amounts are typical of the winter and spring months. The fall months generally
have low rainfall totals and storms during this time occur less frequently than during the other months. For larger storm
events, defined here as those where at least one rain gage in the network measured 25.4 mm or greater during the event,
the mean storm depth weighted over the mean storm coverage of 295 km2 was 20.6 mm, while the mean storm duration
was 7.2 h. For these larger events, the summer storms are separated by the least time between events (mean of 116 h)
while the fall events are separated by the greatest time (mean of 291 h). For summer events, rain gage depths for
individual storm events collected by gages separated by 1.9 km or less are likely to be highly correlated (r iÝ 0.9). This
distance increases to 9.2 km for the winter. High correlations (r iÝ 0.9) are expected up to distances of 5 km throughout
most of the year, except summer. This analysis establishes the basis for detailed modeling across this and other
watersheds in the region.
TL;DR: A long-lived highly organized highly organized squall line moved rapidly across the middle Mississippi and Ohio Valleys on 15 April 1994 within a moderately unstable, strongly sheared environment as discussed by the authors.
Abstract: A long-lived highly organized squall line moved rapidly across the middle Mississippi and Ohio Valleys on 15 April 1994 within a moderately unstable, strongly sheared environment. Over Kentucky and southern Indiana, the line contained several bowing segments (bow echoes) that resulted in widespread wind damage, numerous shear vortices/rotational circulations, and several tornadoes that produced F0–F2 damage. In this study, the Louisville–Fort Knox WSR-88D is used to present a thorough discussion of a particularly long-tracked bowing line segment over central Kentucky that exhibited a very complex and detailed evolution, more so than any other segment throughout the life span of the squall line. Specifically, this segment produced abundant straight-line wind damage; cyclic, multiple core cyclonic circulations, some of which met mesocyclone criteria; several tornadoes; and embedded high precipitation supercell-like structure that evolved into a rotating comma head–comma tail pattern. The bowing seg...
TL;DR: In this paper, the first three Schumann resonance (SR) modes observed at Nagycenk (47.6°N, 16.7°E) indicate a southward shift in the global position of the lightning activity in warm El Niňo years and a northward shift on the longitudinal range where Africa dominates the activity.
Abstract: The self-consistent behavior of the frequency level and semiannual intensity variations of the first three Schumann resonance (SR) modes observed at Nagycenk (47.6°N, 16.7°E) indicates a southward shift in the global position of the lightning activity in warm El Niňo years and a northward shift in cool La Niňa years, especially in the longitudinal range where Africa dominates the activity. The third SR mode has a crucial role in recognizing these meridional shifts due to the special angular distance of Nagycenk with respect to the African thunderstorm region. The diurnal zonal redistribution of the worldwide thunderstorm activity manifests in characteristic daily frequency patterns. The preserved daily frequency patterns with changing frequency levels in the same months of the different years imply that the meridional shifts of the lightning activity exist in worldwide sense on the ENSO time scale. The estimated shifts are about 4–8° in latitude.
TL;DR: In this paper, the authors used a three-dimensional off-line chemical transport model (CTM) to assess the impact of lightning emissions in the free troposphere both on NO x itself and on other chemical species such as O 3 and OH.
TL;DR: In situ measurements of cloud properties, NO, and other trace gases were made in active thunderstorms by two research aircraft as mentioned in this paper, and concurrent measurements from a 3D VHF interferometer and the 2D National Lightning Detection Network were used to determine lightning frequency and location.
Abstract: In situ measurements of cloud properties, NO, and other trace gases were made in active thunderstorms by two research aircraft. Concurrent measurements from a three-dimensional (3-D) VHF interferometer and the 2-D National Lightning Detection Network were used to determine lightning frequency and location. The CHILL Doppler radar and the NOAA-WP-3D Orion X band Doppler radar were also used to measure storm characteristics. Two case studies from the (STERAO) Stratosphere-Troposphere Experiments: Radiation, Aerosols, and Ozone project in northeastern Colorado during the summer of 1996 are presented. Narrow spikes (0.11–0.96 km across), containing up to 19 ppbv of NO, were observed in the storms. Most were located in or downwind of electrically active regions where the NO produced by lightning would be expected. However, it was difficult to correlate individual flashes with NO spikes. A simple model of the plume of NO from lightning is used to estimate NO production from the mean mixing ratio measured in these spikes. The estimates range from 2.0×1020 to 1.0×1022 molecules of NO per meter of flash length.
TL;DR: In this article, extreme wind speeds during thunderstorms and non-thunderstorms are studied in Singapore and it is shown that while extreme TS gust speeds are consistently higher than those of NTS, extreme mean wind speeds for TS are smaller than those for NTS.
TL;DR: In this article, the authors measured the charge and size of precipitation particles with an instrumented free balloon in a convective mountain thunderstorm over Langmuir Laboratory in central New Mexico.
Abstract: We measured the charge and size of precipitation particles with an instrumented free balloon in a convective mountain thunderstorm over Langmuir Laboratory in central New Mexico. Using an instrument that measured precipitation charge from 2 to 220 pC and equivalent particle diameters from 0.6 to 3.8 mm, we deduced that (1) the charge of the main positive charge region is carried by cloud particles, the charge of the main negative charge region is carried by a mixture of negative charge bearing cloud particles and precipitation particles, and the charge of the lower positive charge region is carried almost entirely by precipitation; (2) there was a mixture of both polarities of precipitation charge at nearly all altitudes; (3) there was no relationship between precipitation charge and size; (4) our charge data appear to support the noninductive ice-ice collisional charging mechanism; and (5) the sign of charge carried by the precipitation reverses with ambient temperature. In comparing these data to previous measurements that were collected in New Mexico mountain thunderstorms with different instrumentation, we found that in most ways our precipitation charge data are similar to the previous measurements. In comparing these data with data that we previously collected in the trailing stratiform regions of mesoscale convective systems, we found that there are substantial differences in the precipitation charge data between these different cloud types.
TL;DR: In this paper, a new parameterization of the thunderstorm cloud electrical flash frequency is obtained on the basis of simple dimensional arguments, where flash frequency was expressed as a power function of both the cloud top height and the cloud droplet concentration, thus partly taking into account the role of the microphysical cloud characteristics.
Abstract: In this work, a new parameterization of the thunderstorm cloud electrical flash frequency is obtained on the basis of simple dimensional arguments. The flash frequency is expressed as a power function of both the cloud top height and the cloud droplet concentration, thus partly taking into account the role of the microphysical cloud characteristics. Since droplet concentrations are not predicted by General Circulation Models (GCMs) and further show great variability, two different “standard” droplet concentrations, respectively valid for continental and maritime thunderstorms, are used. A numerical experiment has been made by using the METEO-France GCM “ARPEGE” in relation to both, this new parameterization and the Price and Rind (1992) parameterization, in order to determine the global characteristics of electrical flashes. The analysis of the results reveals that the mean annual global flash frequency as well as the total number of flashes that strike annually the globe are higher when the new parameterization is used but are in better agreement with the Optical Transient Detector (OTD) (Christian et al., 1996) observations, thus indirectly attesting for its validity. Further, the good agreement between monthly and diurnal global flash numbers and the corresponding OTD observations confirms the ability of “ARPEGE” of correctly representing the global thunderstorm development. Finally, the new parameterization has been used in a second numerical experiment in order to infer the role of a doubling of CO2 on the global distribution of electrical flashes. A 10% increase of the mean global annual flash frequency is obtained for a surface warming of roughly 2°C.
TL;DR: In this article, the role of lightning in the production of nitrogen oxides and their subsequent distribution by thunderstorms was investigated by the field experiment LINOX (lightning produced NOx), which was performed in southern Germany in 1996.
Abstract: This paper investigates the role of lightning in the production of nitrogen oxides (NOx) and their subsequent distribution by thunderstorms. These questions were addressed by the field experiment LINOX (lightning produced NOx), which was performed in southern Germany in July 1996. The structure of thunderstorms was observed by radar and satellite, the lightning activity was recorded by a lightning detection network, and airborne chemical measurements were performed aboard a jet aircraft penetrating the storm anvils. NOx concentrations in the storm anvils were found to typically range from 1 to 4 parts per billion by volume. The NO contribution to the total NOx was found to be dominant in narrow peaks produced by flashes as well as near cloud boundaries, probably because of increased photolysis rates of NO2. Using CO2 as an air mass tracer, the lightning-produced NOx amount was discriminated from the contribution due to transport of air from the boundary layer. It was found from a case study of a large storm anvil that lightning-produced NOx was present in the same order of magnitude as the amount of NOx originating from lower levels; during later stages of cloud development, the content of the former even exceeded the latter one. A simple two-dimensional model of advection and dispersion of the lightning-produced NOx was able to reproduce the general structure of the anvil NOx plume. Some NOx peaks could directly be attributed to flash observations close to the aircraft track.
TL;DR: The relationship between the IR cloud-top patterns associated with mesoscale convective systems and the underlying precipitation is not well understood as mentioned in this paper, but it has been recognized in recent years that the majority of tropical precipitation is produced by MCSs and the assumption that the coldest cloud tops are associated with deep active convection has been central to the characterization of cloud system motion and organization, and to many IR-based rainfall retrievals.
Abstract: Precipitation estimation over the tropical oceans is commonly performed using passive infrared (IR) measurements of cloud-top brightness temperature from geostationary satellites to infer the location of deep convection. It has been recognized in recent years that the majority of tropical precipitation is produced by mesoscale convective systems (MCSs). However, the relationship between the IR cloud-top patterns associated with MCSs and the underlying precipitation is not well understood. The assumption that the coldest cloud tops are associated with deep, active convection has been central to the characterization of cloud system motion and organization, and to many IR-based rainfall retrievals. Previous studies suggested that this view may be oversimplified when applied to propagating convective systems, such as squall lines. The goal of this study was to understand the evolution of the cold cloud associated with tropical oceanic squall line MCSs, and to discuss the implications for the retrieva...
TL;DR: In this article, the T-28 aircraft in the CaPE project in Florida was observed at −5°C level or higher, and the signature regions were characterised by a relatively high linear depolarization ratio along with relatively low differential reflectivity.
Abstract: Various procedures for inferring hydrometeor characteristics from polarimetric radar data have indicated that regions with echoes exhibiting relatively high linear depolarization ratios along with relatively low differential reflectivity contain wet graupel or hail. Such particles could be found either in a melting zone below the 0°C level in a cloud or in a region of wet growth where the rate of supercooled cloud water accretion overwhelms the rate at which the latent heat associated with complete freezing can be dissipated. In subtropical clouds such as those studied in the Convection and Precipitation/Electrification (CaPE) project in Florida, at the −5°C level or higher, neither condition is obtained. Yet similar polarimetric radar signatures were nevertheless observed at such levels during CaPE. Examination of in situ observations by the T-28 aircraft in the Florida clouds, along with results from previous laboratory and theoretical studies, suggests that the signature regions were character...
TL;DR: In this paper, the performance of the WSR-88D rainfall algorithm, Precipitation Processing System, was examined in detail to determine how well it performed, in particular the sensitivity to the algorithm's rain-rate threshold (hail cap) parameter and the performance on the resulting radar rainfall estimates.
Abstract: A strong thunderstorm produced a flash flood on the evening of 12 July 1996 in Buffalo Creek, Colorado, that caused two deaths and significant property damage. Most of the rain fell in a 1-h time period from 2000 to 2100 MDT. The performance of the WSR-88D rainfall algorithm, Precipitation Processing System, was examined in detail to determine how well it performed. In particular the sensitivity to the algorithm’s rain-rate threshold (hail cap) parameter and the performance of the gauge–radar adjustment subalgorithm on the resulting radar rainfall estimates were examined by comparison with available rain gauge data. It was determined that the WSR-88D rainfall algorithm overestimated the rainfall in general over the radar scanning domain for this event by about 60% relative to the rain gauges although the radar-derived rainfall for the flood-producing storm cell nearly matched the single gauge that sampled it. The derived rainfall over the radar scanning domain was not very sensitive to the settin...
01 Jan 1999
TL;DR: In this paper, a continuous jet impinging on a wall has been used to simulate the downdraft in a thunderstorm, and velocity and turbulence characteristics have been studied at various distances from the stagnation position and over a topographic feature.
Abstract: In this study, a continuous jet impinging on a wall has been used to simulate the downdraft in a thunderstorm. Velocity and turbulence characteristics have been studied at various distances from the stagnation position and over a topographic feature. Comparisons with earlier jet flow studies confirm that speedup over topography is weaker for jet flows than for boundary layer flows, but perhaps not as weak as previously observed.
TL;DR: In this paper, the authors deduce temporal variations of the level of global lightning activity from the long-term Schumann resonance (SR) monitoring performed at the Tottori observatory (35.5°N, 134.33°E).
Abstract: We deduce temporal variations of the level of global lightning activity from the long-term Schumann resonance (SR) monitoring performed at the Tottori observatory (35.5°N, 134.33°E). The continuous analog records of the horizontal magnetic field cover the period from August 1967 to November 1970. The data show that temporal changes of the SR amplitudes vary considerably from day to day. Meanwhile, the regular diurnal and longer-scale variations appear after averaging. We found annual, and semiannual components in variations of global thunderstorm activity between 1967 and 1970. Comparison with the long-term SR records made recently in Europe allows us to demonstrate the similarity and stability of the global thunderstorm variations on a seasonal scale. Simultaneously, it revealed a contribution from winter thunderstorms in the Japan Sea to the Tottori SR records.
TL;DR: In this article, two objective forecasting methods are developed using data from May and June for 1985-89, namely, graphical technique and multiple regression method to predict the occurrence/nonoccurrence of thunderstorms.
Abstract: Accurate prediction of thunderstorms during the pre-monsoon season (April–June) in India is essential for human activities such as construction, aviation and agriculture. Two objective forecasting methods are developed using data from May and June for 1985–89. The developed methods are tested with independent data sets of the recent years, namely May and June for the years 1994 and 1995. The first method is based on a graphical technique. Fifteen different types of stability index are used in combinations of different pairs. It is found that Showalter index versus Totals total index and Jefferson's modified index versus George index can cluster cases of occurrence of thunderstorms mixed with a few cases of non-occurrence along a zone. The zones are demarcated and further sub-zones are created for clarity. The probability of occurrence/non-occurrence of thunderstorms in each sub-zone is then calculated. The second approach uses a multiple regression method to predict the occurrence/nonoccurrence of thunderstorms. A total of 274 potential predictors are subjected to stepwise screening and nine significant predictors are selected to formulate a multiple regression equation that gives the forecast in probabilistic terms. Out of the two methods tested, it is found that the multiple regression method gives consistently better results with developmental as well as independent data sets; it is a potential method for operational use. Copyright © 1999 Royal Meteorological Society
TL;DR: The daily evolution of local surface conditions at Phoenix, Arizona and the characteristics of the 1200 UTC sounding at Tucson, Arizona, have been examined to determine important meteorological features that lead to thunderstorm occurrence over the low deserts of central Arizona.
Abstract: The daily evolution of local surface conditions at Phoenix, Arizona, and the characteristics of the 1200 UTC sounding at Tucson, Arizona, have been examined to determine important meteorological features that lead to thunderstorm occurrence over the low deserts of central Arizona. Each day of July and August during the period 1990–95 has been stratified based upon daily mean, surface moisture conditions at Phoenix, Arizona, and the occurrence of afternoon and evening convective activity in the Phoenix metropolitan area. The nearest operational sounding, taken 160 km to the southeast at Tucson, is shown to be not representative of low-level thermodynamic conditions in central Arizona. Thus, Phoenix forecasters’ ability to identify precursor conditions for the development of thunderstorms is impaired. On days that convective storms occur in the Phoenix area, there is a decrease in the diurnal amplitude of surface dewpoint changes, signifying increased/deeper boundary layer moisture. This signal is ...
TL;DR: In this article, the convective available potential energy (CAPE) and the wind shear were retrieved from radio soundings from Munchen and Stuttgart from 1992 to 1996.
Abstract: The motion of thunderstorms in southern Germany was investigated. The thunderstorms were observed by a lightning position system during the summer months of the years 1992–1996. On average every second day thunderstorms were observed somewhere in southern Germany. In general thunderstorms approached from westerly and south-westerly directions. The average speed was 13 m s−1. No significant relation between the occurrence of thunderstorms and the large-scale synoptic pattern described by the Grosswetterlagen (large-scale weather pattern) was found. Thunderstorms were observed during almost all Grosswetterlagen. The reduction to eight weather patterns based on the low-level flow in southern Germany showed that thunderstorms are likely when the flow has a westerly (43%) or easterly direction (20%). Three distinct groups of different lighting patterns could be identified: stationary, moving thunderstorms and thunderstorm lines. The convective available potential energy (CAPE) and the wind shear were retrieved from radio soundings from Munchen and Stuttgart. On average CAPE was 583 J kg−1 for stationary thunderstorms, 701 J kg−1 for moving thunderstorms and 876 J kg−1 for thunderstorm lines. The corresponding average bulk Richardson numbers were 37, 22 and 21. The steering level was found to be at about 6 km m.s.l. However, it should be noted that in most cases the soundings do not completely describe the local environment of thunderstorms, since radio soundings are only available twice a day. Copyright © 1999 Royal Meteorological Society