Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

This paper reviews recent progress in the study and understanding of extreme seasonal events in the Amazon region, focusing on drought and floods. The review includes a history of droughts and floods in the past, in the present and some discussions on future extremes in the context of climate change and its impacts on the Amazon region. Several extreme hydrological events, some of them characterized as ‘once in a century’, have been reported in the Amazon region during the last decade. While abundant rainfall in various sectors of the basin has determined extreme floods along the river's main stem in 1953, 1989, 1999, 2009, 2012–2015, deficient rainfall in 1912, 1926, 1963, 1980, 1983, 1995, 1997, 1998, 2005 and 2010 has caused anomalously low river levels, and an increase in the risk and number of fires in the region, with consequences for humans. This is consistent with changes in the variability of the hydrometeorology of the basin and suggests that extreme hydrological events have been more frequent in the last two decades. Some of these intense/reduced rainfalls and subsequent floods/droughts were associated (but not exclusively) with La Nina/El Nino events. In addition, moisture transport anomalies from the tropical Atlantic into Amazonia, and from northern to southern Amazonia alter the water cycle in the region year-to-year. We also assess the impacts of such extremes on natural and human systems in the region, considering ecological, economic and societal impacts in urban and rural areas, particularly during the recent decades. In the context of the future climate change, studies show a large range of uncertainty, but suggest that drought might intensify through the 21st century.

Extreme seasonal droughts and floods in Amazonia: causes, trends and impacts

Lightning and climate: A review

Observation of the vertical profile of precipitation over the global Tropics is a key objective of the Tropical Rainfall Measuring Mission (TRMM) because this information is central to obtaining vertical profiles of latent heating. This study combines both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine “wet-season” vertical structures of tropical precipitation across a broad spectrum of locations in the global Tropics. TRMM-PR reflectivity data (2A25 algorithm) were utilized to produce seasonal mean three-dimensional relative frequency histograms and precipitation ice water contents over grid boxes of approximately 5°–10° in latitude and longitude. The reflectivity histograms and ice water contents were then combined with LIS lightning flash densities and 2A25 mean rainfall rates to examine regional relationships between precipitation vertical structure, precipitation processes, and lightning production. Analysis of the reflectivity vertical structure histograms ...

/pdf/regional-variability-in-tropical-convection-observations-16hcg85lpi.pdf

Regional Variability in Tropical Convection: Observations from TRMM

Previous total lightning climatology studies using Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) observations were reported at coarse resolution (0.5°) and employed significant spatial and temporal smoothing to account for sampling limitations of TRMM’s tropical to subtropical low-Earth-orbit coverage. The analysis reported here uses a 16-yr reprocessed dataset to create a very high-resolution (0.1°) climatology with no further spatial averaging. This analysis reveals that Earth’s principal lightning hotspot occurs over Lake Maracaibo in Venezuela, while the highest flash rate density hotspot previously found at the lower 0.5°-resolution sampling was found in the Congo basin in Africa. Lake Maracaibo’s pattern of convergent windflow (mountain–valley, lake, and sea breezes) occurs over the warm lake waters nearly year-round and contributes to nocturnal thunderstorm development 297 days per year on average. These thunderstorms are very localized, and their persistent deve...

Where Are the Lightning Hotspots on Earth

This paper describes the results of monthly latitudinal (8Â°-30Â° N) and latitude belts (8Â°-10Â°, 10Â°-15Â°, 15Â°-20Â°, 20Â°-25Â°, and 25Â°-30Â°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.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD02592

Thunderstorm activity over India and the Indian southwest monsoon

[1] Spatio-temporal variability of lightning activity over the Indian land mass region (8°N–33°N, 73°E–86°E) has been studied using monthly satellite based lightning flash grid (5° × 5°) data for 5-year (1998–2002) period. These data have been examined for depicting the annual, seasonal, and spatial distribution of the lightning activity. The study revealed the nonlinear relationship between lightning flash density and latitude on the annual timescale, and it is linked with the convective activity, large-scale circulations, land mass gradient, and orography of the region under study. On the seasonal timescale, the nonlinear positive relationships were observed in the premonsoon and monsoon seasons whereas a bimodal variation is observed in the post-monsoon season. The comparison of flash density with maximum surface air temperature shows the existence of nonlinear relationship between the two parameters. The approximate range of increase of flash density per 1°C rise in temperature is 20 to 44%. The lightning flash density shows a pronounced semiannual oscillation over the latitude belts 8°N–28°N.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004JD005631

Spatio-temporal variability of lightning activity over the Indian region

[1] Satellite (LIS) based lightning flash grid (0.5° × 0.5°) data for the Indian land mass region covering from 8°–33°N and 73°–86°E for a period of 4 years (1998–2001) were used to study the diurnal variation with one hour time resolution. The analysis revealed that there exists a strong diurnal cycle in the lightning activity with a prominent peak around 1000 UTC. An examination of seasonal diurnal variation suggests that the lightning activity was found highest in premonsoon and lowest in the postmonsoon season.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003GL018005

Diurnal variation of lightning activity over the Indian region

This work presents the association of flash rate density (FRD) with surface air temperature, rainfall and convective available potential energy (CAPE) using satellite-based flash count grid (0.5° × 0.5°) data from 1998 to 2007 over Maharashtra, India. We investigate monthly to seasonal variations in lightning activity with rainfall and CAPE. The first peaks for FRD and rainfall found in June and July, respectively, followed by next peaks in September. The difference in peaks for FRD and rainfall of 1 month (June–July) attributed to the onset phase of summer monsoon in June (relatively less wet period favorable for more convective and lightning activity), thereafter, heavy rainfall in July over Maharashtra. The annual variations show that the September peaks for both FRD and rainfall are higher than that in June for FRD and for rainfall in July. FRD is moderately correlated with rainfall (r = 0.51 at significant level <0.0001). There is good parallelism in the variation of FRD, and CAPE as the correlation coefficient in between them is 0.78 at significant level <0.0001.

Lightning activity and its association with rainfall and convective available potential energy over Maharashtra, India

Thirty years (1951-1980) of mean monthly thunderstorms days (TS) and rainfall (RF) amounts for 260 Indian observatories spread uniformly over the country were used to obtain their monthly, seasonal and zonal percentage of occurrence from all India totals. The study has revealed that there is a time lag of one month in the occurrence of peak activity of TS and RF. Seasonal analysis of these two parameters suggest that rainfall yield associated with postmonsoon season TS seems to be higher than the premonsoon season. Six zone analysis of TS and RF has suggested that there exists a wide range of variation in both parameters month after month in that zones, but the 30 year mean percentage of occurrence seems to be more or less equal in magnitude in each zone.

/pdf/study-of-thunderstorm-and-rainfall-activity-over-the-indian-14lcbaywx8.pdf

M. I. R. Tinmaker

Papers

Thunderstorm activity over India and the Indian southwest monsoon

Spatio-temporal variability of lightning activity over the Indian region

Diurnal variation of lightning activity over the Indian region

Lightning activity and its association with rainfall and convective available potential energy over Maharashtra, India

Study of thunderstorm and rainfall activity over the Indian region