Pookkandy Byju

Climate change is expected to have a considerable impact on precipitation leading to more intense and frequent extreme events. Considering the different driving mechanisms of precipitation extreme is essential to understand the changes in response to climate change. In this study, we decompose the intensity of extreme wet month precipitation (EWMP) during the Indian summer monsoon (ISM) into atmospheric dynamic, thermodynamic and non‐linear components by using moisture budget estimation. The data from 19 Coupled Model Intercomparison Project phase‐6 (CMIP6) models are used for historical, intermediate (SSP2‐4.5), and high‐emission (SSP5‐8.5) scenarios and the changes are estimated for near (2021–2040), mid (2041–2060), and far‐future (2081–2100) relative to the historical (1995–2014) period for different monsoon sub‐domains. The findings reveal a significant increase in the intensity of EWMP in the ISM, projecting 2%–12% in SSP2‐4.5 and 8%–25% in SSP5‐8.5 for the far‐future. The enhanced vertical ascent of moisture (V‐Dyn) is found to be a dominant factor contributing more than 70% to EWMP in most sub‐domains. However, regardless of enhancement in intensity of precipitation, the models simulate a reduction in impact of the V‐Dyn by 10%–35% from the near to far‐future period, particularly in high emission scenarios. Vertical thermodynamic and non‐linear moisture advection components also play minor roles (15% in SSP5‐8.5). The responses also vary regionally for components such as horizontal dynamic term, where it leads to precipitation offset in the northern regions, but causes enhanced precipitation in southern regions. The study highlights the spatial and temporal variability of moisture budgets of extreme wet Indian summer monsoon precipitation in a warming environment.

Sea surface temperature anomalies (SSTA) in portions of the extratropics are known to recur from one winter to the next without persisting through the intervening summer. Previous studies identified only a limited number of midlatitude regions where this reemergence occurs. Here we find that most of the global oceans exhibit winter‐to‐winter recurrence of SSTA. Indeed, recurrence of SSTA is the default process in the global ocean. Only regions strongly linked to El Niño do not show signs of SST reemergence. In midlatitudes, the temperature anomalies that recur persist below the shallow mixed layer in summer. However, SST recurrence is also found at some tropical locations and appears to be independent of subsurface ocean heat storage. Reemergence at these locations is linked to the recurrence of atmospheric drivers of SSTA, predominantly the wind‐stress forcing. Our results are supported by different ocean data sets and by state‐of‐the‐art climate model simulations.

The high‐frequency time series data collected during 28th October to 21st November 2006 onboard R/V Mirai provided the first evidence of short‐term bio‐physical coupling in the central equatorial Indian Ocean (EIO). The predominant feature of the thermal structure was the down‐sloping of 28°C‐isotherm and up‐sloping of 14°C‐isotherm indicating deepening of surface‐layer and shoaling of lower‐thermocline respectively. Concomitant with the deepening of surface‐layer, nitracline and subsurface chlorophyll maximum (SCM) also deepened. From the prominent bi‐weekly periodicity in the 14°C‐isotherm and the upward phase propagation in the meridional current velocity, we infer that shoaling was the response of mixed Rossby‐Gravity (MRG) waves. Based on temperature and currents we propose that deepening of surface‐layer was caused by the eastward advection of warmer waters associated with the weakening of Indian Ocean Dipole (IOD). This made the upper ocean more nutrient‐depleted and biologically less‐productive, an indication that the central EIO is returning to its pre‐IOD condition.

The present study investigates the conditions leading to the formation of a cyclone over the Arabian Sea using in situ, buoy, Argo floats, island, satellite, reanalysis and blended datasets. Cyclogenesis parameters, such as the sea-surface temperature (SST), the mid-tropospheric relative humidity (MTRH), the relative vorticity (RV) and the vertical wind shear (VWS), were examined. Furthermore, the variability of different parameters from satellite data, such as the SST, the outgoing longwave radiation (OLR), the precipitable water (PW), the rainfall rate and wind speed (WS), were also investigated from the pre-disturbance stage to the cyclonic stage. An analysis of the dynamic and thermodynamic cyclogenesis parameters from the reanalysis data showed that the MTRH, RV and PW increased dramatically from the pre-disturbance stage to the depression stage by 150%, 530% and 32%, respectively. It is envisaged that better spatial and temporal satellite estimates of the OLR, SST, PW, blended Objectively Analyzed air–sea Flux (OAFlux) project, European Centre for Medium Range Weather Forecast (ECMWF) data products and new tools, such as moored buoys and Argo floats, would be useful for the study of cyclones over the Arabian Sea.