Madathiparambil Ranganathapai Ramesh Kumar

We review the major conceptual models of atmospheric moisture transport, which describe the link between evaporation from the ocean and precipitation over the continents. We begin by summarizing some of the basic aspects of the structure and geographical distribution of the two major mechanisms of atmospheric moisture transport, namely low-level jets (LLJs) and atmospheric rivers (ARs). We then focus on a regional analysis of the role of these mechanisms in extreme precipitation events with particular attention to the intensification (or reduction) of moisture transport and the outcome, in terms of precipitation anomalies and subsequent flooding (drought), and consider changes in the position and occurrence of LLJs and ARs with respect to any associated flooding or drought. We then conclude with a graphical summary of the impacts of precipitation extremes, highlighting the usefulness of this information to hydrologists and policymakers, and describe some future research challenges including the effects of possible changes to ARs and LLJs within the context of future warmer climates.

We characterize the climatological features of the double inter-tropical convergence zones (DITCZs) over the western Indian Ocean during November–December by a synergistic analysis of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite (HOAPS III) data (1988–2005) and the National Aeronautics and Space Administration's (NASA's) A-Train data (2002–2009). We investigate rainfall, freshwater flux and cloud liquid water, cloud fraction and relative humidity over the DITCZs. In addition, the daily rainfall data from the Global Precipitation Climatology Project (GPCP) are used to document the DITCZs during the El Niño southern oscillation (ENSO) events. An analysis of the GPCP data shows that the DITCZs are clearly discernible during strong ENSO events (1997, 2002 and 2006), in sharp contrast to the DITCZs in the eastern Pacific Ocean, where they are absent during ENSOs. Further, these convergence zones on either side of the equator are of short duration, approximately 3–6 pentads during November and December. All satellite sensor data sets consistently capture the major features of DITCZs. As an accurate simulation of DITCZs in coupled global climate models remains a challenge, the results from the present study would provide a platform for evaluating these models.

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.