Influence of PDO on South Asian summer monsoon and monsoon–ENSO relation

This study has investigated the possible relation between the Indian summer monsoon and the Pacific Decadal Oscillation (PDO) observed in the sea surface temperature (SST) of the North Pacific Ocean. Using long records of observations and coupled model (NCAR CCSM4) simulation, this study has found that the warm (cold) phase of the PDO is associated with deficit (excess) rainfall over India. The PDO extends its influence to the tropical Pacific and modifies the relation between the monsoon rainfall and El Niño-Southern Oscillation (ENSO). During the warm PDO period, the impact of El Niño (La Niña) on the monsoon rainfall is enhanced (reduced). A hypothesis put forward for the mechanism by which PDO affects the monsoon starts with the seasonal footprinting of SST from the North Pacific to the subtropical Pacific. This condition affects the trade winds, and either strengthens or weakens the Walker circulation over the Pacific and Indian Oceans depending on the phase of the PDO. The associated Hadley circulation in the monsoon region determines the impact of PDO on the monsoon rainfall. We suggest that knowing the phase of PDO may lead to better long-term prediction of the seasonal monsoon rainfall and the impact of ENSO on monsoon.     

Characterization of the 26 December 2004 tsunami deposits in Andaman Islands (Bay of Bengal, India)

The large tsunami, which was generated by an earthquake on 26 December 2004, affected most of the countries around the Indian Ocean. A total of 48 tsunamigenic surface sediments and nine core samples have been collected from various coastal geomorphological features such as beaches, estuaries/creeks and mangrove areas in the Andaman Islands. These samples were analysed for textural analysis and geochemical studies to evaluate effects of the tsunami on sediment contamination. The studied sediments, deposited by the 26 December 2004 tsunami in Andaman group of islands, belong to poorly sorted, coarse to medium sands. Generally the concentration of heavy metals in the tsunamigenic surface sediments is mainly in the order of Cu > Mn > Fe > Zn > Pb during the post-tsunami (2005) and Cu > Fe > Mn > Zn > Pb during the post-monsoon (2008). The analysed core samples show that tsunami sediments have been preserved at certain depths from the sampling locations and indicate that they were derived from shallow littoral to neritic depths. The approximate width of deposits deposited by the 26 December 2004 Tsunami in Diglipur and Mayabandar areas (North Andaman) is ~10 cm, in Rangat and Baratang (Middle Andaman) the thickness of the deposits is ~15 cm. In Chidiyatapu, Junglighat, Rutland Islands and Havelock Island (South Andaman) the thickness of the deposits is ~30, ~8, ~25 and ~5 cm, respectively, and in Hut Bay (Little Andaman) the thickness of the deposits is about ~15 cm.