5The Bay of Bengal (BoB) plays a fundamental role in controlling the weather systems that make up the South Asian summer monsoon system. In particular, the southern BoB has cooler sea surface temperature (SST) that influence ocean-atmosphere interaction and impact on the monsoon. Compared to the southeast, the southwestern BoB is cooler, more saline, receives much less rain, and is influenced by the Summer Monsoon Current (SMC). To examine the impact of these features on the monsoon, the BoB Boundary Layer Experiment (BoBBLE) was jointly undertaken by India and the UK during June

No abstract

No abstract

Deformation rates derived from GPS measurements made at two continuously operating stations at Leh (34.1°N, 77.6°E) and Hanle (32.7°N, 78.9°E), and eight campaign sites in the trans-Himalayan Ladakh spanning 11 years (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008), provide a clear picture of the kinematics of this region as well as the convergence rate across northwestern Himalaya. All the Ladakh sites move 32-34 mm/year NE in the ITRF2005 reference frame, and their relative velocities are 13-16 mm/year SW in the Indian reference frame and *19 mm/year W with reference to the Lhasa IGS station in southeastern Tibet. The results indicate that there is no statistically significant deformation in the 200-km stretch between the continuous sites Leh and Hanle as well as between Leh and Nubra valley sites along the Karakoram fault, whereas the sites in and around the splayed Karakoram fault region indicate surface deformation of 2.5 mm/year. Campaign sites along the Karakoram fault zone indicate a fault parallel surface motion of 1.4-2.5 mm/year in the Tangste and western Panamik segment of the Karakoram fault, which quantifies the best possible GPS-derived dextral slip rate of 3 mm/ year along this fault during this 11-year period. Baselines of Ladakh sites show convergence rates of 15-18 mm/year with respect to south India and 12-15 mm/year with respect to Delhi in north India and Almora in the Himalaya *400 km north-northeast of Delhi. These constitute an arc normal convergence of 12-15 mm/year across the western Himalaya, which is consistent with arc normal convergence all along the Himalayan arc from west to east. Baseline extension rates of 14-16 mm/year between Lhasa and Ladakh sites are consistent with the east-west extension rate of Tibetan Plateau.

The India-Eurasia collision, driven by tectonic forcing, is modulated by nontectonic forcing allied to seasonal variations in the neighboring regions. To decipher the ground deformation in response to hydrological mass variations of the Himalaya and North India, we analyzed continuous Global Positioning System (cGPS) observations from 50 sites together with Gravity Recovery and Climate Experiment (GRACE) data for the period 2004-2015. Vertical components of surface deformation derived from GPS and GRACE show moderate to high-level amplitude correlation with a slope value of 0.76 and a level of phase delay from ±25°to ±30°. The average weighted root-mean-square reduction (WRMS) of 17.72% suggests the prominence of hydrological mass variations particularly over the sub-Himalaya and Indo-Gangetic Plain (IGP). GPS-derived vertical deformation after correcting the hydrological effects utilizing GRACE observations suggests that the sub-Himalaya and IGP are undergoing subsidence and the surrounding areas show uplift. In addition to the tectonic and nontectonic forcings, an unsustainable consumption of groundwater associated to irrigation and other anthropogenic uses influence the subsidence rate in the IGP and sub-Himalaya. Further, 2-D elastic dislocation modeling suggests that GRACE correction to the GPS vertical velocity causes a reduction in the subsurface slip rate estimation over the Main Himalayan Thrust (MHT) system by 12.06% and improves the chi-square misfit by 20.32%.