BoBBLE: Ocean–Atmosphere Interaction and Its Impact on the South Asian Monsoon (original) (raw)
Related papers
BOBMEX: The Bay of Bengal Monsoon Experiment
Bulletin of The American Meteorological Society, 2001
The first observational experiment under the Indian Climate Research Programme, called the Bay of Bengal Monsoon Experiment (BOBMEX), was carried out during July-August 1999. BOBMEX was aimed at measurements of important variables of the atmosphere, ocean, and their interface to gain deeper insight into some of the processes that govern the variability of organized convection over the bay. Simultaneous time series observations were carried out in the northern and southern Bay of Bengal from ships and moored buoys. About 80 scientists from 15 different institutions in India collaborated during BOBMEX to make observations in most-hostile conditions of the raging monsoon. In this paper, the objectives and the design of BOBMEX are described and some initial results presented.
Journal of Climate, 2018
Time series of surface meteorology and air–sea fluxes from the northern Bay of Bengal are analyzed, quantifying annual and seasonal means, variability, and the potential for surface fluxes to contribute significantly to variability in surface temperature and salinity. Strong signals were associated with solar insolation and its modulation by cloud cover, and, in the 5- to 50-day range, with intraseasonal oscillations (ISOs). The northeast (NE) monsoon (DJF) was typically cloud free, with strong latent heat loss and several moderate wind events, and had the only seasonal mean ocean heat loss. The spring intermonsoon (MAM) was cloud free and had light winds and the strongest ocean heating. Strong ISOs and Tropical Cyclone Komen were seen in the southwest (SW) monsoon (JJA), when 65% of the 2.2-m total rain fell, and oceanic mean heating was small. The fall intermonsoon (SON) initially had moderate convective systems and mean ocean heating, with a transition to drier winds and mean oce...
ASIRI: An Ocean-Atmosphere Initiative for Bay of Bengal
Bulletin of the American Meteorological Society, 2016
Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view ...
The Onset of the Monsoon over the Bay of Bengal: The Observed Common Features for 2008–2011
Atmospheric and Oceanic Science Letters
In situ buoy observation data spanning four years (2008-2011) were collected and used to perform a composite analysis of the monsoon onset process in the Bay of Bengal (BoB). The sea surface temperature (SST) in the central BoB increases dramatically during the monsoon transition period and reaches its annual maximum just before the onset of the monsoon. This process is illustrated by the northward-propagating deep convection phase of the intraseasonal oscillation and the establishment of a steady southwest wind. It is argued that the SST peak plays a potential role in triggering the onset of the monsoon in the BoB and its vicinity. The general picture of the BoB monsoon onset summarized here reveals the possibility of regional land-ocean-atmosphere interaction. This possibility deserves further examination.
MAUSAM, 2021
The observed short term. variability in .the current field of the upper layers of the northern Bay of Bengal IS examined utilizing the available time series data sets of current meter records obtained from mooring lines deployed from USSR stationary ship polygons during MONSOON-77 and MONEX-79 field experiments. Supplementary time series data sets on the vertical profiles of temperature and salinity in addition to surface winds were also made use of to describe the observed variability and structure of the horizontal velocity in the upper 200 m water column. Although the thermal regime appeared to be homogeneous within both the observational arrays considerable differences were noticed in the salinity and current regimes. The strong vertical stratification which is variable in the northern Bay of Bengal appeared to have Influenced the observed upper oceanic flow regime. Evidence for Ekman type of balance was rather weak suggesting the importance of baroclinic and river driven circul...
Journal of Geophysical Research, 2002
1] An analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon (June-September). In the Arabian Sea the winds associated with the summer monsoon are stronger and favor the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer. The weak winds are also unable to overcome the strong near-surface stratification because of a lowsalinity surface layer. This leads to a shallow surface mixed layer that is stable and responds quickly to changes in the atmosphere. An implication is that sea surface temperature (SST) in the bay remains higher than 28°C, thereby supporting large-scale deep convection in the atmosphere during the summer monsoon. The atmospheric heating associated with the convection plays a critical role in sustaining the monsoon winds, and the rainfall associated with it, not only over the bay but also over the Indian subcontinent, maintains a low-salinity surface layer. In the Arabian Sea the strong overturning and mixing lead to lower SST and weak convective activity, which in turn, lead to low rainfall and runoff, resulting in weak stratification that can be overcome easily by the strong monsoon winds. Thus, in both basins, there is a cycle with positive feedback, but the cycles work in opposite directions. This locks monsoon convective activity primarily to the bay.
Journal of Climate
The mechanisms involved in the onset of the Bay of Bengal summer monsoon (BOBSM) were studied using reanalysis data and numerical model experiments. Results revealed that the weak meridional land–sea thermal contrast (LSTC) over the northern BOB in early spring enhances the lower-tropospheric easterly belt along 10°–15°N, which is unfavorable for the BOBSM onset. The BOBSM onset is driven by the cumulative impact of this LSTC along with the LSTC in the meridional direction across the equator and in the zonal direction across the tropics, together with air–sea interactions. While the LSTC intensifies over the northern BOB, a near-surface northward cross-equatorial flow develops south of India, inducing springtime zonal flow and surface sensible heating over the southern BOB and a pair of cyclones straddling the equator over the central Indian Ocean at 700 hPa. The zonal LSTC in the tropics generates near-surface cyclones over land and anticyclones over the sea. This induces a zonal S...
Air-sea interaction over the Indian Ocean during the contrasting monsoon years 2002 and 2003
Geophysical Research Letters, 2005
1] The air sea interaction processes over the Indian Ocean are studied using the satellite data from the Tropical Rainfall Measuring Mission Satellite for two contrasting monsoon years, namely 2002 (deficit) and 2003 (normal). The moisture transport for the two contrasting years was also analyzed using the NCEP/NCAR reanalysis data. Linear correlation coefficient between the convective heating over the Bay of Bengal and the zonal wind at 850 hPa over the peninsular India showed the maximum negative correlation (-0.41) and is statistically significant at 99.9% significance level with a lag of 3 days, with convection leading. The evaporation rates were lower (higher) over the Arabian Sea during active (weak) monsoon conditions, indicating its negligible influence on the ensuing monsoon activity over the subcontinent. Water vapor contents decreased substantially prior to the break over the Arabian Sea and low values prevailed throughout the break period. Further, it was seen that more moisture was transported into the subcontinent (equatorial region) during the active (weak) monsoon conditions.