Northeast India (NEI), the wettest place on the Earth, has experienced a rapid decrease in summer monsoon rainfall (about 355 mm) in the last 36 years (1979–2014), which has serious implications on the ecosystem and the livelihood of the people of this region. However, it is not clear whether the observed drying is due to anthropogenic activities or it is linked with the global natural variability. A diagnostic model is employed to estimate the amount of recycled rainfall, which suggests that about 7% of the total rainfall is contributed by the local moisture recycling and decrease in recycled rainfall is about 30–50 mm. Using gridded observed rainfall and sea surface temperature data of the last 114 years (1901–2014), here we show that the recent decreasing trend of NEI summer monsoon rainfall is rather associated with the strong interdecadal variability of the subtropical Pacific Ocean. The strong interdecadal variability over NEI suggests a possibility of skillful decadal prediction of the monsoon rainfall, which may have important implications in terms of long‐term planning and mitigation.

Abstract:We show that the non-minimal coupling of tachyon field to the scalar curvature, as proposed by Piao et al, with the chosen coupling parameter does not produce the effective potential where the tachyon field can roll down from T = 0 to large T along the slope of the potential. We find a correct choice of the parameters which ensures this requirement and support slow-roll inflation. However, we find that the cosmological parameter found from the analysis of the theory are not in the range obtained from observations. We then invoke warped compactification and varying dilaton field over the compact manifold, as proposed by Raeymaekers, to show that in such a setup the observed parameter space can be ensured.

Several reanalysis data sets are being used for understanding the role of environmental factors controlling tropical cyclones (TCs) evolution. Six reanalysis data sets, namely, European Center for Medium‐range Weather Forecast (ECMWF) ERA‐Interim (ERAI) reanalysis, Global Forecast System (GFS) analysis, Japan Meteorological Agency's 55‐year reanalysis projects reanalysis (JRA55), Modern‐Era Retrospective Analysis for Research and Applications, version 2 (MERRA2) reanalysis, NCEP Climate Forecast System Reanalysis (CFSR), and fifth generation of ECMWF atmospheric reanalysis of global climate (ERA5), have been evaluated for the representation of track, intensity, and structure of 28 TCs which occurred over North Indian Ocean (NIO) during the period 2006–2015. The errors in track, intensity, and minimum sea level pressure (MSLP) of TCs are estimated with respect to the best track data set of India Meteorological Department (IMD). The representation of inner core structure of TCs has been compared. The smallest error in the position of TCs center, MSLP, and maximum wind speed is found in GFS analysis followed by ERA5 and CFSR reanalysis, respectively. GFS and CFSR data sets capture the most intense stages of the TCs followed by the ERA5 data set, while the other three are unable to obtain intensification beyond the severe cyclonic storm stage. The structures of TCs are better represented in GFS analysis followed by ERA5 reanalysis. However, GFS analysis represents early intensification and, in some cases, overprediction of the category of TCs, especially during the most intensified stages (beyond cyclonic storms). Thus, GFS analysis captures the evolution of TCs more realistically, followed by the ERA5 reanalysis data set.

We analyze warm tachyonic inflation, proposed in the literature , but from the viewpoint of four dimensional effective action for tachyon field on a non-BPS D3-brane. We find that consistency with observational data on density perturbation and validity of effective action requires warped compactification. The number of background branes which source the flux is found to be of the order of 10 in contrast to the order of 10 14 in the standard cold inflationary scenario.

Numerical simulations of a thunderstorm event that occurred in the pre‐monsoon season over the North‐Eastern region of India (NEI) and Bangladesh are performed using Weather Research and Forecasting (WRF) Advanced Research Weather Research and Forecasting Model (ARW, version 3.8.1). Doppler weather radar indicates severe convective activity lasted for more than 10 hr. These extremely deep convective clouds with minimum cloud‐top temperature −70 °C at 19 km were triggered by the mixing of a moist air mass transported from the Bay of Bengal in the south and dry air transported from the northwest. A cyclonic circulation observed over the Tibetan plateau is likely to be associated with the strong southerly low‐level wind over NEI, as the plateau acts as a source of heat‐lows during the pre‐monsoon season. The coexistence of ice particles and supercooled water in the storms resulted in a large number of lightning flashes during the storm as observed from the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (TRMM‐LIS). Co‐location of supercooled cloud water droplets helps in forming graupel through riming that plays a vital role in these convective systems. Lightning flashes calculated from WRF simulation using the Morrison microphysical and cloud top height based dynamical lightning parametrization scheme was found comparable with the observed flashes from TRMM‐LIS. Since the WRF model could simulate the thunderstorm, we recommend using this state‐of‐the‐art regional model in thunderstorm and lightning predictions for northeast India which would be useful in preparedness for such extreme events.