查看更多>>摘要：During the pre-monsoon season in the Eastern and North-eastern Indian regions, thunderstorms are the primary source of precipitation. The intensity and frequency of these thunderstorms are changing over time in these areas. The knowledge of atmospheric instability associated with these pre-monsoon thunderstorms can be aptly collected using thermodynamic indices. Thermodynamic indices integrate the comprehending convective at-mosphere's geographical and temporal interpretation and are crucial in thunderstorm nowcasting. The present work investigated the spatial variation of thermodynamic indices for 1987-2016 over two tropical north-eastern states of India (Assam and Tripura) using the ERA-5 reanalysis data with 0.25 x 0.25 (31 km) resolution. The analysis incorporated information on thunderstorm days (TD) and non-thunderstorm days (NTD) provided by the India Meteorological Department (IMD) for differentiating the spatial variations of thermodynamic indices. The thermodynamic indices used in this work are categorised as conditional, potential, and convective instabilities. The results reveal that indices associated with convective and potential instabilities perform better for differ-entiating thunderstorms. We have incorporated the Man-Kendall trend analysis to investigate the trends in the spatial variation of thermodynamic indices. The results indicate that the region is showing higher instability for thunderstorm occurrences on TD, and there is higher moisture availability for the area during the whole pre-monsoon season. The inhibition is higher over NTD days, limiting the convective activity occurrence on certain days. The severity of thunderstorms as analysed with the help of thermodynamic indices are not changing over the region.
查看更多>>摘要：High spatial and temporal resolution measurements from the Indian Geostationary satellite 'Kalpana-1' have been utilized to find the relation between the convection and upper tropospheric humidity (UTH). The analysis reveals that the UTH leads deep convection by 2-4 h over Indian landmass, which is attributed to the advection associated with tropical easterly jet rather than the direct overshooting monsoon convection. In contradiction, the UTH lags convection by 2-6 h over nearby oceans, indicating that direct overshooting convection plays a major role in moistening the upper troposphere. A new mechanism is proposed in which, if the UTH leads to deep convection, thick and dense high-altitude clouds form that can lead to negative feedback to convection through radiative cooling. If UTH lags convection then thin clouds form, thereby can result in positive feedback for convection. However, this feedback to convection is controlled by the presence of the TEJ.
查看更多>>摘要：Western Ghat (WG) mountains along the west coast of peninsular India play an important role in the distribution of monsoon rainfall on its windward and leeward sides. The study unravels the increase in cloudiness and also increase in the Cloud Enhancement of Solar irradiance (CES) during the dry and wet seasons in the windward (high altitude) and the leeward (low altitude) sides of WG. From May 2018 to May 2021, the global horizontal irradiance (GHI) reveals wide temporal and spatial variability with a high frequency of CES events, even exceeding the extraterrestrial value around the noontime during the wet season (May to October). The observed excess irradiance due to partial/transparent clouds compared to clear sky maxima is more than 400 W/m(2) on the windward and 350 W/m(2) on the leeward. With the increase in cloudy days, diffused irradiance also increased with greater values during CES events. CES induced positive shortwave cloud radiative forcing (CRF) varied up to +400 W/m(2) (warming effect), while negative CRF varied up to-1000 W/m(2) (cooling effect). During monsoon, the warming due to frequent CES events could locally offset a large cooling to some extent. Clouds resulting in huge irradiance variability in a day could also induce large fluctuations in renewable solar energy. Such short-term sporadic local events are averaged out in satellite data.
查看更多>>摘要：Due to contents of the dry air and water vapor, troposphere affects radio signals of the space geodetic techniques (e.g., GNSS and VLBI) as range delays. These tropospheric delays should be eliminated to achieve precise point positioning. Over the years, researchers have been developed many of troposphere model. However, the existing models differ from each other in their resolution, data source used and especially in their accuracy. In this paper, a new troposphere model has been presented. The new model considers annual, semi annual and diurnal effects in both sine and cosine form unlike its ancestors. ERA5's monthly averaged hourly dataset has been used to produce the new model. In order to validate new model, the data of ERA5 and terrestrial meteorological stations have been used. Moreover, zenith tropospheric delay (ZTD) values obtained by the new model have been validated by IGS products. Accuracy of the ZTD values has been obtained 3.15 cm. According to the results, it can be concluded that including diurnal effects in both sine and cosine forms improves the accuracies of determined parameters.
NSTL
Elsevier