| In this study,we investigated the flash duration,spatial size,optical radiance and their associations with thunderstorm structures in the Asia-Pacific region ranging from 70°E to160°E and from 18°N to 36°N with six specially chosen regions.Firstly,the geographical distributions of flash duration,length,footprint and optical radiance were investigated by employing flash data collected by the Lightning Imaging Sensor?LIS?aboard the Tropical Rainfall Measuring Mission?TRMM?satellite from 2002 to 2014.Then,the characteristics of monthly variation and probability distribution of flash properties during the daytime and nighttime periods,as well as the correlation between flash spatial-temporal scale and optical radiance were analyzed.Finally,the matched LIS flash data and RPF?Radar Precipitation Feature?thunderstorm data were used to establish correspondence between the flash properties and thunderstorm structures.The main conclusions are as follows:Geographical distributions of flash properties:?1?The flash density value was,on average,large over the land,and small over the ocean.However,the spatial distribution of spatial-temporal scale and optical radiance of flash were large over the ocean and small over the land.From a regional perspective,the flash density,the spatial-temporal scale and optical radiance of flash were not simply reversed.Overall,from the east to the west of China,flash density,spatial-temporal scale and optical radiance were all changed from large to small.?2?As a whole,the ocean-land differences in flash properties,were more distinct in the warm season than in the cold season.The seasonal comparison was distinct in some certain areas.Notably,while the mean flash spatial size and optical radiance values over the northern part of the Indian Peninsula were low in both seasons,the mean flash duration was relatively large in the cold season but small in the warm season.In the cold season,the flashes over the ocean and part of Japan in the northern part of the study region had a short mean duration but a very strong mean optical radiance.?3?The flashes over offshore waters near the east coast of China had the longest mean duration,while the flashes over the ocean of southern part of the analyzed area had the largest mean length and footprint,and the flashes over the ocean to the east of Japan had the greatest mean optical radiance.Monthly variations of flash properties:?1?The monthly variation of the flash spatial scale and optical radiance was roughly unanimous,except for the ocean to the east of Japan,while the monthly variation of the flash duration was significantly different from the monthly variation of the flash spatial and optical radiance in many regions and different time.?2?The inverse correlations of flash activity with flash spatial size and optical radiance in the monthly variation was relatively obvious over the land and uncertain over the ocean.In addition,it was found that the monthly variation of some flash properties over some regions were different between the daytime and nighttime periods.In the month of active flash activity?May to August?,the spatial scale and optical radiance of flash were relatively small and vice versa.The monthly variation of flash length and optical radiance over the deep ocean were similar to that of flash density,while the peak value occurred in summer?June to August?.Numerical statistics and distributions of flash properties:?1?Flash spatial scale and optical radiance had a log-normal distribution both in the daytime and nighttime.In the small range,the probability distribution of the land flash samples was larger than that of the ocean.The peak distribution interval of flash durations in the six chosen regions was located in 00.1s.The peak distribution interval of flash length over land was 812 km,while 1216 km over ocean.And the peak was located in 100200 km2 for flash footprint and 00.2 J m-2 sr-1?m-1for flash optical radiance.?2?The flashes over the OFS had the longest mean duration,while the flashes over the PLA had the shortest mean duration during both the daytime and nighttime period.The length of flashes over the DPO had the maximum mean flash optical radiance during both two periods,while the minimum mean flash footprint occurred over the PLA during daytime and over the SHF during nighttime.The optical radiance of flashes over the OEJ had the maximum mean flash optical radiance during both two periods,while the minimum mean flash optical radiance occurred over the PLA during daytime and the SHF during nighttime.?3?The best positive correlation was between length and footprint,as they both characterize the spatial scale of the flash.There was a relatively strong correlation between flash spatial size and optical radiance;however,the relationships of flash duration with flash spatial size and optical radiance were weak.Comparisons of flashes and RPFs properties:?1?Comparisons of flash properties with thunderstorm properties in the cold and warm seasons showed that a positive correlation between flash spatial size and RPF area and a negative correlation between flash spatial size and flash density of RPFs?it can be used as a proxy for the convective intensity of thunderstorm?existed in the studied regions except for the DPO.?2?Comparisons of flash properties with thunderstorm properties in different areas showed that the median RPF area over the ocean was larger than that over the land,while the mean spatial size and optical radiance of flash over the ocean were larger than over the land.If the PLA was taken out of the consideration,the flash spatial size and optical radiance generally exhibited an inverse correlation with the flash density of RPFs over other regions,indicating that the stronger thunderstorms tends to had small-size and low-power flashes.?3?The flashes with top 10%longest duration,greatest length and largest optical radiance were more likely to occur in thunderstorms with high altitude and large area than the flashes with bottom 10% properties. |
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