Global warming hiatus contributed weakening of the Mascarene High in the Southern Indian Ocean.

The Mascarene High (MH) is a semi-permanent subtropical high-pressure zone in the South Indian Ocean. Apart from its large influence on African and Australian weather patterns, it also helps in driving the inter-hemispheric circulation between the Indian Ocean in the south and subcontinental landmass in the north. Using observations and reanalysis products, this study for the first time investigates recent warming trend observed in the MH region during the Global Warming Hiatus (GWH) period (1998-2016). Significant positive trends are observed in sea surface temperature (SST), sea surface height (SSH) and oceanic heat content (OHC) during this period in the MH region. Mixed layer heat budget analysis reveals the dominant role of heat advection in the observed warming trend. During the GWH period, stronger zonal currents advect the warm waters from the Western Pacific (WP) towards the MH region via the Indonesian Throughflow (ITF). This warming in the MH reduces the sea level pressure therein and establishes a weak pressure gradient between the MH and the northern hemisphere landmass. This in-turn weakens the cross-equatorial winds in the western Indian Ocean.

Author Correction: Global warming hiatus contributed weakening of the Mascarene High in the Southern Indian Ocean.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Intensification of tidally generated internal waves in the north-central Bay of Bengal.

Flow of barotropic tidal currents over topographic features, such as continental slopes and submarine ridges, generates internal gravity waves at tidal periods known as internal tides. Amplitude of these waves are generally large near the generation regions. Analysis of Sea Surface Height (SSH) data, derived from satellite altimeter revealed the amplification of internal tides in the semidiurnal period in the north-central Bay of Bengal (BoB) (around 89[Formula: see text]E, 16[Formula: see text]N), which is about 450 km away from their generation sites. SSH signals found in the north-central BoB ([Formula: see text]3 cm) were comparable to the maximum amplitudes (2.5 to 3.5 cm) observed near their potential generation sites in the BoB such as continental slopes in the head of the bay and Andaman-Nicobar (AN) Ridge. Simulations from a high-resolution regional ocean model also confirmed the presence of large internal tide amplitude in the north-central BoB. Our study revealed that convergence of internal tides, which were generated along the concave-shaped source (continental slopes in the head of the bay and the northern parts of AN Ridge), into its focal region caused their amplification in the north-central BoB. It was also found that internal tide energy dissipation rates in this focal region were about 10 times larger than those in other open ocean regions.