Flash Counts Research Articles

Lightning activity, rainfall and flash flooding – occasional or interrelated events? A case study in the island of Crete

Abstract. The majority of cyclones passing over Crete in late autumn to early winter originate from southwest, west and northwest and are of varying size and intensity. A number of these cyclones cause flash floods. The present study reports the possible relationships between lighting activity and high precipitation related to flash flood events. In this study an attempt was made to correlate the lightning number and location, recorded by the ZEUS lightning detection system, with the rainfall characteristics for sixteen rain events (4 flood and 12 non-flood events) on the island of Crete, during the period 2008–2009. Spatiotemporal analysis of rain and rain rate with flash count was performed with respect to distance (radius) of flashes from raingauge location at various temporal scales, in order to examine the correlation of accumulated rainfall and lightning activity. The maximum attained statistical significant correlation was obtained within a circular area of an average radius of 15 km around the raingauge, and an average time lag of flash count prior precipitation accumulation of 15 min. The maximum correlation between the lightning and rainfall data is obtained for shorter time lags for the flood events (15 min) than the non-flood events (25 min), that could reflect the faster propagation of flood triggering storms due to high convective activity. Results show increased lightning activity occurring during flood triggering storms, by an average of four times higher. Furthermore, there is evidence that the number of flashes that occur during a precipitation event is related to precipitation depth when the latter is adequate to produce a flood event. Differences between flood and non-flood producing storms need to be further assessed by analyzing more independent parameters, including the synoptic conditions and dominant flash flood hydrological generating processes.

熱帯降雨観測衛星TRMMを用いたアフリカ大陸熱帯域における雷活動と降水の季節変化

We analyzed seasonal variations of lightning activity in continental tropical Africa using 10-day, monthly, and seasonal data observed by the Tropical Rainfall Measuring Mission (TRMM) satellite. The data collected were flash counts obtained with Lightning Imaging Sensor (LIS), and total rainfall, convective rainfall, and stratiform rainfall obtained with Precipitation Radar (PR) for the 10-year period 1998-2007. The overall flash count migrates seasonally and meridionally following the solar angle, while it is abundant throughout the year at low latitudes near the equator. Flash count maximum areas generally occur over mountainous regions and the maximum frequency is observed in the Mitumba Mountains east of the Congo Basin. The flash count is also high in the central Congo Basin regardless of season. In the central region (7.5–12.5°N, along 20–22.5°E) of the African Continent, another maximum flash count area is observed during the period May–October. The maximum zone of total rainfall from May to August occurs between these two maxima of the flash count. The peak region of the flash count from December to March does not coincide with that of total rainfall. The maximum region of the flash count occurs from the equator to 2.5°S, while that of total rainfall occurs between 7.5° and 12.5°S. The maximum region of the flash count and total rainfall in January and March is separated by about 10° of latitude. Along 22.5°E, in the central region of the African Continent, the flash count at 10°N is higher both at the beginning and final stages of the warm season rainfall. In contrast, the flash count is high only at the beginning of the warm season rainfall at 10°S. The beginning of warm season rainfall relative to the solar angle is 2 months earlier at 10°S.

Interactions of numerical and temporal stimulus characteristics on the control of response location by brief flashes of light

Pigeons pecked on three keys, responses to one of which could be reinforced after 3 flashes of the houselight, to a second key after 6, and to a third key after 12. The flashes were arranged according to variable-interval schedules. Response allocation among the keys was a function of the number of flashes. When flashes were omitted, transitions occurred very late. Increasing flash duration produced a leftward shift in the transitions along a number axis. Increasing reinforcement probability produced a leftward shift, and decreasing reinforcement probability produced a rightward shift. Intermixing different flash rates within sessions separated allocations: Faster flash rates shifted the functions sooner in real time, but later in terms of flash count, and conversely for slower flash rates. A model of control by fading memories of number and time was proposed.

Diurnal and spatial variabilities of monsoonal CG lightning and precipitation and their association with the synoptic weather conditions over South Korea

The spatial and temporal variations in cloud-to-ground (CG) lightning and precipitation during the summer monsoon months in Korea have been analyzed in relation to the regional synoptic weather conditions. The lightning data used in this study were collected from a lightning detection network installed by the Korean Meteorological Administration, while the precipitation data were collected from 386 Automatic Weather Stations spread over the entire Korean Peninsula during 2000 to 2001. A distinctive morning peak of precipitation is observed over the midwest region of Korea. Along the east coast, little precipitation and CG flash counts are found. Despite the strong afternoon peaks of convective rainfall due to the high elevation over the southern inland region, the south coast shows nocturnal or early morning peaks, which represents a common oceanic pattern of flash counts. In 2000, the nighttime peak for lightning counts dominates over the southern area, while the afternoon peak was strong in the midland during the summer, mainly due to the northward transportation of moisture to the Korean Peninsula. Conversely, the strong afternoon peak for the southern region was confronted with early morning peaks in the midwestern region during 2001. The eastward transport of moisture has been analyzed and was considered to be dominant in 2001. The study of several warm and cold type fronts in 2000 and 2001 indicate that the warm type fronts in 2000 were associated with very little lightning, while the cold type fronts appeared to be responsible for the occurrence of abundant lightning in 2001, thereby, indicating that the warm and cold type fronts were representative of the local lightning distribution in the respective years.

A study of lightning activity over land and oceanic regions of India

Monthly variations of lightning activity over typical land and oceanic regions of India were examined using satellite data (OTD) for a 5-year period (1995–1999). It is noted that the nature of variation between surface air maximum temperature (T max), thunderstorm days (Thn), and lightning flash count over ER and WR showed remarkable correspondence and sensitivity with each other on monthly time scale. As we move out of winter season and enter the monsoon season, via pre-monsoon season, the WR undergoes cooling relative to the ER in the range 0.1–1.2°C. As a result, WR experiences reduction of thunder days and lowering in flash count. This decrease in T max, Thn, and flash count over WR may also be associated with relatively small values of T θw and CAPE in comparison with similar values over ER during the monsoon season. Our observation of associated reduction in Thn and lightning count per 1°C cooling in surface air maximum temperature suggests reduction of ∼3.5 thunderstorms per station and 73 flashes. Comparison of lightning flashes between pairs of coastal, oceanic, arid-zone, hilly, and island stations reveals distinct relationship between climate regime and intensity of lightning activity. We may conclude the results of this study by saying that the overhead lightning activity is a clear reflection of the status of the underlying ground-earth properties. A close and continuous monitoring of lightning activity may be considered as a need of present day scientific studies.

Seasonal variation of lightning activity over the Indian subcontinent

The seasonal variation of lightning flash activity over the Indian subcontinent (0°N–35°N and 60°E–100°E) is studied using the quality checked monthly lightning flash data obtained from lightning imaging sensor on board the Tropical Rainfall Measuring Mission satellite. This paper presents results of spatio-temporal variability of lightning activity over the Indian subcontinent. The study of seasonal total lightning flashes indicates that the lightning flash density values are in qualitative agreement with the convective activity observed over this region. Maximum seasonal total flash counts are observed during the monsoon season. The propagation of the inter-tropical convergence zone over this region is also confirmed. Synoptic conditions responsible for variation of lightning activity are also investigated with the help of an observed dataset. The mean monthly flash counts show a peak in the month of May, which is the month of maximum temperatures over this region. Maximum flash density (40.2 km−2 season−1) is observed during the pre-monsoon season at 25.2°N/91.6°E and the annual maximum flash density of 28.2 km−2 year−1 is observed at 33.2°N/74.6°E. The study of the inter-annual variability of flash counts exhibits bimodal nature with the first maximum in April/May and second maximum in August/September.

Concurrent Cloud-to-Ground Lightning and Precipitation Enhancement in the Atlanta, Georgia (United States), Urban Region

AbstractThis study explores how the Atlanta, Georgia (United States), urban region influences warm-season (May through September) cloud-to-ground lightning flashes and precipitation. Eight years (1995–2003) of flashes from the National Lightning Detection Network and mean accumulated precipitation from the North American Regional Reanalysis model were mapped under seven different wind speed and direction combinations derived from cluster analysis. Overlays of these data affirmed a consistent coupling of lightning and precipitation enhancement around Atlanta. Maxima in precipitation and lightning shifted in response to changes in wind direction. Differences in the patterns of flash metrics (flash counts versus thunderstorm counts), the absence of any strong urban signal in the flashes of individual thunderstorms, and the scales over which flashes and precipitation enhancement developed are discussed in light of their support for land-cover- and aerosol-based mechanisms of urban weather modification. This study verifies Atlanta’s propensity to conjointly enhance cloud-to-ground lightning and precipitation production in the absence of strong synoptic forcing. However, because of variability in aerosol characteristics and the dynamics of land use change, it may be a simplification to assume that this observed enhancement will be persistent across all scales of analysis.

A Perfect Prognosis Scheme for Forecasting Warm-Season Lightning over Florida

Abstract This study develops and evaluates a statistical scheme for forecasting warm-season lightning over Florida. Four warm seasons of analysis data from the Rapid Update Cycle (RUC) and lightning data from the National Lightning Detection Network are used in a perfect prognosis technique to develop a high-resolution, gridded forecast guidance product for warm-season cloud-to-ground (CG) lightning over Florida. The most important RUC-derived parameters are used to develop equations producing 3-hourly spatial probability forecasts for one or more CG flashes, as well as the probability of exceeding various flash count percentile thresholds. Binary logistic regression is used to develop the equations for one or more flashes, while a negative binomial model is used to predict the amount of lightning, conditional on one or more flashes occurring. The scheme is applied to output from three mesoscale models during an independent test period (the 2006 warm season). The evaluation is performed using output from the National Centers for Environmental Prediction (NCEP) 13-km RUC (RUC13), the NCEP 12-km North American Mesoscale Model, and local high-resolution runs of the Weather Research and Forecasting (WRF) Model for a domain over south Florida. Forecasts from all three mesoscale models generally show positive skill through the 2100–2359 UTC period with respect to a model containing only climatology and persistence (L-CLIPER) and persistence alone. A forecast example using the high-resolution WRF Model is shown for 16–17 August 2006. Although the exact timing and placement of forecast lightning are not perfect, there generally is good agreement between the forecasts and their verification, with most of the observed lightning occurring within the higher forecast probability contours.

Urban Lightning: Current Research, Methods, and the Geographical Perspective

AbstractThis review of urban lightning research begins with a description of cloud‐to‐ground flash data and some of the conditioning practices related to their use. Urban lightning studies from the United States and internationally are then examined to distill findings as well as to compare and contrast the modes of inquiry among the meteorologists, climatologists, engineers, and geographers who study lightning. In summary, these investigations convey how urban heating, building‐induced surface friction, aerosols, and specificities such as local physiography and synoptic setting are intertwined causal mechanisms underlying urban flash modification. A tension among methodological approaches in these studies circumscribes how questions are posed, and how findings are valued and ultimately synthesized. Flash research tends to follow either a descriptive phenomenological approach or a foundational approach in which prediction and mechanism are paramount. Selecting the spatial extent of an urban lightning study and the methods to assess the statistical embeddedness of flash counts within thunderstorms events are two other methodological points of contention. City‐to‐city comparisons and integrated analysis of aerosols, precipitation, and flashes over multiple scales are important directions for future research.

Diurnal variations in lightning activity over Swaziland as observed from Space: 1998-2006

Lightning phenomena have recently gained a lot of interest among researchers mainly due to its impact on the human and natural environment. The thermodynamics of lightning and its distribution on the landscape are, therefore, under intense investigation in many part of the world, mainly in the developed world. In this report, nine years of lightning data (January 1998 to December 2006) from the Lightning Imaging Sensor on board the Tropical Rainfall Measuring Mission (TRMM) satellite was used to analyse the diurnal frequency of lightning frequency over Swaziland, a country characterized by a complex terrain. Through geographic information systems analysis of the lightning flash counts, which was corrected for detection efficiency and instrument view time, was analysed to reveal diurnal patterns in lightning activity across the four climatic seasons and the country’s four eco-climatic (physiographic) zones. Results showed a pronounced evidence of bimodal peaks, mainly in summer (52%) and autumn (28%), during the late afternoon and evening (1400 and 2000 hours), accounting for 60% of the total hourly flashes, and a second peak during the late evening hours (2200-0000 hours), which were found to be for 27% of the hourly total. The time of maximum lightning frequently occurred mainly over the elevated areas of the Highveld) (37%), Middleveld (32%) and Lowveld (24%), resulting from updrafts caused by topographic lifting. This suggests the presence of convective development and stratiform precipitation according to the local and meso-scale circulation weather system affecting the country. The installation of a ground-based system is recommended, as this would further improve the understanding of the spatial and temporal dynamics of lightning in Swaziland. 1 Swaziland National Trust Commission, P.O. Box 100, Lobamba H107, Swaziland

Diurnal cycles of precipitation, clouds, and lightning in the tropics from 9 years of TRMM observations

The diurnal cycles of surface rainfall, population of precipitation systems, deep intense convection reaching near the tropopause, lightning flash counts, cold clouds, and vertical structure of precipitation are analyzed over the tropics, using 9 years of TRMM Precipitation Radar, Visible and Infrared Scanner, and Lightning Imaging Sensor measurements. The diurnal cycles over land include a late afternoon maximum of precipitation systems, with phase differences among cloud, precipitation, flash counts, and radar echo at different altitudes. Over ocean, the diurnal cycles are interpreted as having contributions from nocturnal precipitation systems and early afternoon showers. There are double peaks of radar reflectivity above 12 km near 0230 and 0530 local time over oceans. The oceanic clouds with infrared brightness temperature < 235 K have two peaks, one during the night and the other in early afternoon.

On perceived synchrony—neural dynamics of audiovisual illusions and suppressions

Whenever temporally incongruent audiovisual sequences are presented, the perceived flash rate follows the physical flutter rate. Increasing the auditory flutter rate increases the perceived flicker rate (visual illusions). Likewise, decreasing the flutter rate decreases the perceived flicker rate (visual suppressions). Here, we investigated the electrophysiological correlates of this perceptual phenomenon. Two sequences of visual flashes and auditory beeps were presented either synchronously (both visual flashes (F) and auditory beeps (B) at 3 or 5 Hz, respectively) or asynchronously at different rates (3F5B or 5F3B). Event-related potentials were acquired, while subjects reported the perceived number of flashes (response options: 3, 4, and 5). During asynchronous trials, subjects' flash counts were significantly higher when the flutter rate exceeded the flicker rate (i.e. visual illusions occurred); and lower flutter rate was below the flicker rate (i.e. visual suppressions occurred). Differential brain responses for reported illusions and suppressions (incorrect flash counts) vs. no-illusions/suppressions (correct flash counts) were found over parieto-occipital sites, followed by slow modulations over frontal and occipital areas. Importantly, the modulation over occipital electrodes starting around 500 ms had an inverse polarity for illusions vs. suppressions. These results provide evidence that both sound-induced visual illusions and suppressions are mediated by an interplay of distributed brain regions, in the attempt to fuse asynchronous audiovisual stimuli into a synchronous percept.

Measurements of reactive nitrogen produced by tropical thunderstorms during BIBLE‐C

The Biomass Burning and Lightning Experiment phase C (BIBLE‐C) aircraft mission was carried out near Darwin, Australia (12°S, 131°E) in December 2000. This was the first aircraft experiment designed to estimate lightning NO production rates in the tropics, where production is considered to be most intense. During the two flights (flights 10 and 13 made on December 9 and 11–12, respectively) enhancements of NOx (NO + NO2) up to 1000 and 1600 parts per trillion by volume (pptv, 10‐s data) were observed at altitudes between 11.5 and 14 km. The Geostationary Meteorological Satellite (GMS) cloud (brightness temperature) data and ground‐based lightning measurements by the Global Positioning and Tracking System (GPATS) indicate that there were intensive lightning events over the coast of the Gulf of Carpentaria, which took place upstream from our measurement area 10 to 14 h prior to the measurements. For these two flights, air in which NOx exceeded 100 pptv extended over 620 × 140 and 400 × 170 km2 (wind direction × perpendicular direction), respectively, suggesting a significant impact of lightning NO production on NOx levels in the tropics. We estimate the amount of NOx observed between 11.5 and 14 km produced by the thunderstorms to be 3.3 and 1.8 × 1029 NO molecules for flights 10 and 13, respectively. By using the GPATS lightning flash count data, column NO production rates are estimated to be 1.9–4.4 and 21–49 × 1025 NO molecules per single flash for these two flight data sets. In these estimations, it is assumed that the column NO production between 0 and 16 km is greater than the observed values between 11.5 and 14 km by a factor of 3.2, which is derived using results reported by Pickering et al. (1998). There are however large uncertainties in the GPATS lightning data in this study and care must be made when the production rates are referred. Uncertainties in these estimates are discussed. The impact on the ozone production rate is also described.

Performance assessment of the Optical Transient Detector and Lightning Imaging Sensor

We describe the clustering algorithm used by the Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) for combining the space‐based observations of lightning pulse data into events, groups, flashes, and areas. Events are single pixels that exceed the LIS/OTD background level during a single frame (2 ms). Groups are clusters of events that occur within the same frame and in adjacent pixels. Flashes are clusters of groups that occur within 330 ms and either 5.5 km (for LIS) or 16.5 km (for OTD) of each other. Areas are clusters of flashes that occur within 16.5 km of each other. The flash data from LIS/OTD are currently being used for lightning and thunderstorm processes and climatological studies; therefore we test how variations in the algorithms for the event‐group and group‐flash clustering affect the flash count for a subset of the LIS and OTD data. We divided the subset into areas with low (1–3), medium (4–15), high (16–63), and very high (64+) flash counts to see how changes in the clustering parameters affect the flash rates in these different sizes of areas. We found that as long as the cluster parameters are within about a factor of two of the current values, the overall flash counts do not change by more than about 20%. Therefore the flash clustering algorithm used by the LIS and OTD sensors are robust and create flash rates that are relatively insensitive to reasonable variations in the clustering algorithms.

Characteristics of cloud-to-ground lightning flashes over Sweden

A detailed study of the characteristics of cloud-to-ground (CG) lightning flashes over Sweden was carried out for the period 1987–2000 using data obtained from the Swedish lightning-locating network. Results are presented by analysing over half a million lightning ground flashes. The average variation of the annual mean of the total number of flashes was found to be 37%. About 12% of the CG flashes were positive flashes and their average variation about the annual mean was 26%. The average peak currents were fairly constant over the years with variations as little as 4% for negative flashes and 5% for positive flashes. The average peak current values for negative and positive flashes were −29.90 and +63.97 kA respectively. A correlation between the mean monthly flash count and percentage of positive flashes was seen. A similar relationship is seen with the mean monthly flash count and the peak currents for both polarities. In general, high flash density and high peak currents were observed in the southern part of Sweden where most of the major cities are located. Flash densities exceeding 0.4 flashes km−2 were observed for several large cities. The maximum flash rate of 32 flashes h−1 within a 10 km radius was seen in Jönköping (14.18°E, 57.78°N) in the province of Småland.

A Statistical Procedure to Forecast Warm Season Lightning over Portions of the Florida Peninsula

Abstract Sixteen years of cloud-to-ground lightning data from the National Lightning Detection Network and morning radiosonde-derived parameters are used to develop a statistical scheme to provide improved forecast guidance for warm season afternoon and evening lightning for 11 areas of the Florida peninsula serviced by Florida Power and Light Corporation (FPL). Logistic regression techniques are used to develop equations predicting whether at least one flash will occur during the noon–midnight period in each area, as well as the amount of lightning that can be expected during this same period, conditional on at least one flash occurring. For the amount of lightning, the best results are achieved by creating four quartile categories of flash count based on climatology, and then using three logistic equations and a decision tree approach to determine the most likely quartile. A combination of forward stepwise screening and cross validation are used to select the best combination of predictors that are most likely to generalize to independent data. Results show the guidance equations to be superior to persistence on both the dependent dataset and during cross validation. The greatest skill scores are achieved for predicting whether at least one flash will occur, as well as predicting the number of flashes to within one quartile of that observed. These results demonstrate that the equations possess forecast skill and will provide useful guidance for the probability and amount of lightning in each of the 11 FPL service areas.

Urban lightning climatology and GIS: An analytical framework from the case study of Atlanta, Georgia

There are three underdeveloped components of urban cloud-to-ground lightning studies: (1) the integration of multiple flash descriptors into more informative summary metrics of flash production, (2) the comparison of flash patterns by thunderstorm type, and (3) the correspondence of urban flashes with underlying land use. We used a GIS to integrate these components as part of an analysis of warm season (May–September) flashes for Atlanta, Georgia, a sprawling region in the thunderstorm-prone southeastern US. Our integrated metric of flash counts and flash days demarcated two large contiguous areas of high flash production in northeast Atlanta. Flashes which developed under conditions related to local surface heating and air mass instability more closely corresponded to urban land uses. Frontally-produced lightning was infrequent over the central city. Instead, peaks in production shifted to the periphery of the urban core, an observation suggestive of building barrier effects.

Cloud-to-ground flash patterns for Atlanta, Georgia (USA) from 1992 to 2003

We analyzed the patterns of cloud-to-ground (CG) lightning flashes around Atlanta, Georgia (USA), a region that has undergone an intense conversion from natural to anthropogenic land uses. For the 12 yr period from 1992 to 2003, annual average CG flash densities of 6 to 8 flashes km -2 emerged around Atlanta. These values are 50 to 75% higher than in the surrounding rural areas, and comparable to flash densities along the Atlantic coast of Georgia. High flash densities extended over a large swath of Atlanta, and into Gwinnett County, a heavily suburbanized, rapidly growing county to the northeast. Urban flash production peaked during the summer (May through June) and exhibited more night and early morning activity (18:00 to 06:00 h) than in surrounding rural areas. Atlanta's higher flash densities do not result from isolated flash production over the city; rather they develop when the large scale atmospheric setting favors widespread lightning throughout the region. Maps of flash counts by interval classes also revealed where flash density maxima emerge in different county regions around the city. A large area of reduced positive polarity flashes developed along the arc of At- lanta's loop highway, Interstate 285. This area also trended south along the corridor of Interstate High- way 75 into central Georgia. This pattern suggests that automobiles may be a source of particulate matter, which is hypothesized to reduce the percentage of positive flashes.

Characteristic Differences of Rainfall and Cloud-to-Ground Lightning Activity over South Korea during the Summer Monsoon Season

Abstract In this paper the characteristic variations of cloud-to-ground (CG) lightning and total precipitation during the Korean summer monsoon (June–August) season have been extensively analyzed for different climate regimes. The data used in this study consist of the monthly CG lightning flash count as detected by the lightning detection network installed at the Korean Meteorological Administration (KMA) and the monthly precipitation data from 23 meteorological observatories spread over the Korean peninsula for a period of 10 yr from 1988 to 1997. Temporal and spatial scales of 1 month and 102 km2, respectively, were considered to determine the seasonal values of rain yield or rain volume per CG flash (defined as the ratio of total precipitation to CG flash count over a common area). Seasonal values of rain yield have been compared with that of monthly values separately. The results of variation of the rain yield during the different months constituting the monsoon season are also presented. Results sho...

Tropospheric ozone over the tropical Atlantic: A satellite perspective

We use satellite sensor measurements to obtain a broad picture of the processes affecting tropical tropospheric O3 production over Africa and the Atlantic in the early part of the year. Terra/MOPITT CO retrievals correlate well with biomass burning fire counts observed by the TRMM/VIRS instrument in Northern Hemisphere savanna regions and allow investigation of the subsequent convection of the biomass burning plume at the intertropical convergence zone and interhemispheric transport. Measurements of NO2 from the ERS‐2/GOME instrument enable identification of two important tropical sources of this O3 precursor, biomass burning and lightning. Good correlation is seen between NO2 retrievals and TRMM/LIS lightning flash observations in southern African regions free of biomass burning, thus indicating a probable lightning source of NOx. The combination of MOPITT CO, GOME NO2, and TRMM fire and lightning flash counts provides a powerful tool for investigating the tropospheric production of O3 precursors. These data are used in conjunction with the MOZART‐2 chemical transport model to investigate the early year tropical Atlantic tropospheric O3 distribution using January 2001 as a case study. Inconsistencies between the various tropical tropospheric O3 column products obtained from EP/TOMS data, and between these products, in situ measurements, and modeling, have led to questions about how the Northern Hemisphere biomass burning is connected to the TOMS derived O3 maximum in the tropical southern Atlantic. We show that the early year tropical O3 distribution is actually characterized by two maxima. The first arises due to biomass burning emissions, is located near the Northern Hemisphere fires, and is most evident in the lower troposphere. The second is located in the southern tropical Atlantic midtroposphere, and results from NOx produced by lightning over southern Africa and South America.