G. K. Manohar

Bio: G. K. Manohar is an academic researcher from Indian Institute of Tropical Meteorology. The author has contributed to research in topics: Thunderstorm & Boundary layer. The author has an hindex of 3, co-authored 4 publications receiving 107 citations.

Thunderstorm activity over India and the Indian southwest monsoon

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.

Impact of a total solar eclipse on surface atmospheric electricity

Abstract: A study of the impact of a total solar eclipse (TSE) on surface atmospheric electricity was made using observations of surface electrical potential gradient, conductivity, and boundary layer parameters recorded during the TSE of February 16, 1980, and on a control day at Raichur. The study showed that with the progressing of the eclipse, as a consequence of inhibited convection, the responses of turbulent mixing in the boundary layer near the ground exhibited diminution and subsequent restoration, respectively. During the next 45 min after the totality, when the surface layer remained stably stratified, the diminution in the potential gradient and the increase in the conductivity was maximum; this was about 60% and 200%, respectively, of their corresponding control day values. This result is in very good agreement with most earlier studies of solar eclipses. The study of the impact of the TSE during 3–4 hours of posteclipse showed significant cooling (∼3°C) of the entire surface air layer and a considerable drop in wind speed over the stretch (1130 km×120 km) of the totality-occupied land region. This significant and systematic phenomenon was responsible for setting up a land-sea breezelike circulation, that is, subsidence/downward air motion over the totality-occupied land region and upward over the noneclipsed land across the totality stretch. This resulted in a considerable aerosol-induced reduction in conductivity and about 5 to 8 times increase in potential gradient during the 3–4 hours of posteclipse. This response of the atmospheric electricity parameters was unlike that observed on the normal days.

Cloud liquid water content responses to hygroscopic seeding of warm clouds

Abstract: The cloud liquid water content (CLWC) data in time and space from a total of 96 pairs of target (T) and control (C) experiments were analyzed in this study to compare the responses of CLWC to hygroscopic seeding of warm clouds. Our results of various approaches taken for this analysis have indicated significant modifications in the CLWC for the T clouds as against C clouds. Analysis of changes in CLWC in the T clouds after and before seeding have pointed out their increasing trend of values with increment in the number of seeded traverse in most cases. These results have shown that CLWC in the T clouds increases following the seeding treatment in the range 9–26%. Similar comparisons in the C clouds have indicated obvious diminution in CLWC that lies in the range 5–11%. These results are the clear indications of influence on microphysical growth and decay of such clouds that arises from hygroscopic seeding and not seeding respectively of warm clouds. Analysis of spatial responses of CLWC to seeding has shown that the optimum effect of seeding may be achieved for a suitable cloud in the altitude range 5750–6250 ft. (a.s.l.) in the Pune area. It is believed that this study has provided adequate support in favor of the hypothesis of hygroscopic seeding of warm clouds.

Regional Variability in Tropical Convection: Observations from TRMM

Abstract: 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 ...

Comprehensive Pattern of Deep Convective Systems over the Tibetan Plateau–South Asian Monsoon Region Based on TRMM Data

Abstract: Diurnal and seasonal variation, intensity, and structure of deep convective systems (DCSs; with 20-dBZ echo tops exceeding 14 km) over the Tibetan Plateau–South Asian monsoon region from the Tibetan Plateau (TP) to the ocean are investigated using 14 yr of Tropical Rainfall Measuring Mission (TRMM) data. Four unique regions characterized by different orography are selected for comparison, including the TP, the southern Himalayan front (SHF), the South Asian subcontinent (SAS), and the ocean. DCSs and intense DCSs (IDCSs; with 40-dBZ echo tops exceeding 10 km) occur more frequently over the continent than over the ocean. About 23% of total DCSs develop into IDCSs in the SHF, followed by the TP (21%) and the SAS (15%), with the least over the ocean (2%). The average 20-dBZ echo-top height of IDCSs exceeds 16 km and 9% of them even exceed 18 km. DCSs and IDCSs are the most frequent over the SHF, especially in the westernmost SHF, where the intensity—in terms of strong radar echo-top (viz., 40 dBZ) he...

Meteorological effects of the eclipse of 11 August 1999 in cloudy and clear conditions

Abstract: Integrated atmospheric measurements were made at two sites in the UK during the total solar eclipse of 11 August 1999. Sensitive high–resolution meteorological observations revealed dynamical atmospheric effects despite the presence of cloud. Short–term eclipse–related changes dominated over temperature, wind speed and wind directions associated with the synoptic conditions, and 35 min period gravity waves were detected in surface–pressure observations. Theoretical calculations for solar radiation changes were compared with observations made during the 97% partial eclipse in clear skies at Reading, Berkshire, and used to predict the radiative changes expected at Camborne, Cornwall, during totality. At Camborne, a vertical array of sensitive fine–wire thermometers was operated with a high–resolution sonic anemometer, logged at 5 Hz. Despite cloudy conditions, which reduced the eclipseinduced thermal perturbations, small temperature and wind changes were detected which were consistent with theory. The cold outflow from the umbra was unambiguously detected for the first time in cloudy conditions.

Evidence of vertical transport of carbon monoxide from Measurements of Pollution in the Troposphere (MOPITT)

Abstract: [1] Vertical profiles of carbon monoxide (CO) mixing ratio retrieved from MOPITT measurements have been analyzed. We find that variations in the vertical structure of CO can be detected in the MOPITT data. The Asian summer monsoon plume in CO is observed for the first time as a strong enhancement of CO in the upper troposphere (UT) over India and southern China indicating the effect of deep convective transport. Similarly, zonal mean height latitude cross-sections for the months of September–December, 2002 indicate deep convective transport of CO from biomass burning in the southern tropics. These findings show that MOPITT CO can provide valuable information on vertical transport phenomena in the troposphere.