This paper documents the production and validation of retrieved rainfall data obtained from satellite-borne microwave radiometers by the Global Satellite Mapping of Precipitation (GSMaP) Project. Using various attributes of precipitation derived from Tropical Rainfall Measuring Mission (TRMM) satellite data, the GSMaP has implemented hydrometeor profiles derived from Precipitation Radar (PR), statistical rain/no-rain classification, and scattering algorithms using polarization-corrected temperatures (PCTs) at 85.5 and 37 GHz. Combined scattering-based surface rainfalls are computed depending on rainfall intensities. PCT85 is not used for stronger rainfalls, because strong depressions of PCT85 are related to tall precipitation-top heights. Therefore, for stronger rainfalls, PCT37 is used, with PCT85 used for weaker rainfalls. With the suspiciously strong rainfalls retrieved from PCT85 deleted, the combined rainfalls correspond well to the PR rain rates over land. The GSMaP algorithm for the TRMM Microwave Imager (TMI) is validated using the TRMM PR, ground radar [Kwajalein (KWAJ) radar and COBRA], and Radar Automated Meteorological Data Acquisition System (AMeDAS) precipitation analysis (RA). Monthly surface rainfalls retrieved from six microwave radiometers (GSMaP_MWR) are compared with the gauge-based dataset. Rain rates retrieved from the TMI (GSMaP_TMI) are in better agreement with the PR estimates over land everywhere except over tropical Africa in the boreal summer. Validation results of the KWAJ radar and COBRA show a good linear relationship for instantaneous rainfall rates, while validation around Japan using the RA shows a good relationship in the warm season. Poor results, connected to weakprecipitation cases, are found in the cold season around Japan.

No abstract

Abstract. The relationship between cloud height and lightning activity is examined using data from the Tropical Rainfall Measuring Mission (TRMM) satellite. Coincident data from the precipitation radar (PR) and Lightning Imaging Sensor aboard the TRMM satellite are used to examine whether lightning flash rate is proportional to the fifth power of cloud top height. This study-is unique in that (1) the relationship between instantaneous rather than maximum storm height and flash rate is obtained and (2) relatively unbiased full data sets for different locations and seasons over the globe are used. The relationship between thunderstorm height and flash rate is nonlinear with large variance. The overall trend shows that flash rate increases exponentially with storm height. Some tall thunderstorms do not have large flash rates, but the reverse situation never occurs. The fifth power dependency that is derived from scaling laws is not inconsistent with, but not necessarily required by, the observed data.

Two types of high-energy events have been detected from thunderstorms. One is "terrestrial gamma-ray flashes" (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting "gamma-ray glows". Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for~100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within~1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.

Using a low‐frequency lightning location system comprising 11 sites, we located preliminary breakdown (PB) processes in 662 intracloud (IC) lightning flashes during the summer of 2013 in Osaka area of Japan. On the basis of three‐dimensional location results, we studied initiation altitude and upward propagation speed of PB processes. PB in most IC flashes has an initiation altitude that ranges from 5 to 10 km with an average of 7.8 km. Vertical speed ranges from 0.5 to 17.8 × 105 m/s with an average of 4.0 × 105 m/s. Vertical speed is closely related with initiation altitude, with IC flashes initiated at higher altitude having lower vertical speed during PB stage. Characteristics of PB pulse trains including pulse rate, pulse amplitude, and pulse width are also analyzed. The relationship between pulse rate and vertical speed has the strongest correlation, suggesting that each PB pulse corresponds to one step of the initial leader during the PB stage. Pulse rate, pulse amplitude, and pulse width all show decreasing trends with increasing initiation altitude and increasing trends with increasing vertical speed. Using a simple model, the step length of the initial leader during the PB stage is estimated. Most of initial leaders have step lengths that range from 40 to 140 m with an average of 113 m. Estimated step length has a strong correlation with initiation altitude, indicating that leaders initiated at higher altitude have longer steps. Based on the results of this study, we speculate that above certain altitude (~12 km), initial leaders in PB stages of IC flashes may only have horizontal propagations. PB processes at very high altitude may also have very weak radiation, so detecting and locating them would be relatively difficult.

No abstract

Previous observations show that some narrow bipolar events (NBEs) can initiate intracloud discharges, but the role of NBE as lightning initiation is still unclear. During the summer of 2013, 827 NBEs were detected with a 3-D LF lightning location system in Osaka, Japan. Out of 638 positive NBEs, 103 occurred as the initial events of lightning flashes. These initiator-type NBEs, called "INBEs" in this paper, are always followed by positive pulse trains whose locations show upward propagations probably from the main negative charge region to the upper positive charge region. Most of INBEs develop into intracloud flashes. Only two INBEs develop into positive ground flashes and five INBEs develop into negative ground flashes. Pulse widths and peak amplitudes of electric field change waveforms of INBEs are almost the same as those of normal NBEs. A major difference is that INBEs have much lower discharge heights. Most of INBEs are lower than 10 km while normal NBEs are mainly higher than 10 km. Characteristics of positive pulse trains following INBEs are closely related with discharge heights of INBEs. Higher INBEs are usually followed by weaker, fewer, and less frequent positive pulses with slower upward propagations. As the height increases to above 10 km, NBEs are usually no longer followed by such positive pulses.

Discharge heights of thousands of narrow bipolar events (NBEs) observed in Guangzhou and Chongqing of China are calculated using time delays between the direct wave signals of NBEs and their ionospheric reflection pairs. The result shows that most positive NBEs occur between 8 and 16 km while most negative NBEs occur between 16 and 19 km. Very few negative NBEs are above 19 km or below 14 km. It is inferred that positive NBEs are produced between main negative charge layer and upper positive charge layer while negative NBEs are produced between upper positive charge layer and negative screening charge layer at the cloud top. Variations of NBE discharge heights in two thunderstorms are analyzed. It seems that NBEs can be produced at any position between corresponding charge layers. Positive NBEs are generally higher in the periods when negative NBEs are also occurring. For a given short time period in a single thunderstorm, negative NBEs are always observed to occur at a higher altitude than positive NBEs, indicating a dividing charge layer between positive NBEs and negative NBEs. The possibility of some NBEs as upward discharges from cloud tops mentioned by previous studies is discussed. Supported by multiple evidences, we believe such possibility is very low; instead, NBEs are produced in vigorous convective surges that develop to the height comparable to the discharge height of NBEs. Differences in height distributions in Guangzhou and Chongqing are analyzed and a hypothesis is put forward that both positive NBEs and negative NBEs can only be produced above certain height. The relationship between this hypothesis and the mechanism for NBE production is discussed.