High-Frequency Mixed Rossby-Gravity Waves in the Mid-Troposphere Triggered Kerala Floods of 2018

2021 ◽  
pp. 2150014
Author(s):  
S. R. Kiran
Keyword(s):  
High Frequency ◽  
Extreme Event ◽  
Deep Convection ◽  
Equatorial Indian Ocean ◽  
Boreal Summer ◽  
The South ◽  
South West ◽  
Rainfall Trends ◽  
South West Monsoon ◽  
The Tropics

Kerala, the South-West coastal state of India, was ravaged by a series of floods during the South-West Monsoon of 2018. The season was marked by severely anomalous rainfall trends, with over 100 mm of departures from the mean daily precipitation in the northern districts of the State. Unlike previous works, this study not only documents the extreme event, but also identifies the tropical dynamics responsible for it. The synoptic disturbances of the tropical Pacific triggered high-frequency Mixed Rossby-Gravity (MRG) waves in the mid-troposphere during Boreal Summer, which meddled with the Monsoon trough, as it propagated westward from the east Equatorial Indian Ocean to the east coast of Africa. Interestingly, these equatorially-trapped waves were found to have teamed up with Madden–Julian Oscillations (MJO) to fuel deep convection in the tropics and caused heavy rainfall over Kerala in 2018.

Anomalous current structure in the eastern equatorial Indian Ocean during the south-west monsoon of 1994

2001 ◽  
Vol 52 (5) ◽  
pp. 727 ◽  
Author(s):  
A. S. Unnikrishnan ◽  
V. S. Murty ◽  
M. T. Babu ◽  
C. K. Gopinathan ◽  
R. J. K. Charyulu
Keyword(s):  
Indian Ocean ◽  
Equatorial Indian Ocean ◽  
Homogeneous Layer ◽  
Surface Mixed Layer ◽  
The South ◽  
Current Structure ◽  
South West ◽  
South West Monsoon ◽  
Eastern Equatorial Indian Ocean ◽  
West Monsoon

Analysis of hydrographic data collected along 80°, 84° and 88°E between 5 °N and 3 °S during peak south-west monsoon (July–August) of 1994 in the eastern equatorial Indian Ocean (EEIO) reveals thermohaline variability and anomalous current structure in the upper ocean. A warm (28.4–28.8°C) and less-saline (33 to 34.8) deep (60-75m) homogeneous layer characterizes the surface mixed layer. The south-west monsoon current, advecting the Arabian Sea High Salinity Water eastwards,appears as an eastward undercurrent (˜50 cm s–1) below 125 m at 80 °E between 1 °and 1.5 °N and in the upper 100 m in the vicinity of the equator with an eastward increase of core velocity between 75 and 100 m. This undercurrent has a transport of 4 Sv at 80 °E. The westward flow in the upper layers north of the equator is anomalous, as the surface winds have an eastward zonal component. The associated westward transport is 44 Sv between 84 °and 88 °E. This equatorial westward flow appears to be influenced by the anomalously strong north-westward coastal current off Sumatra and westward propagating Rossby waves.

scholarly journals The Theory of the South-West Monsoon

Nature ◽  
1922 ◽  
Vol 109 (2726) ◽  
pp. 109-112
Author(s):  
L. C. W. BONACINA
Keyword(s):  
The South ◽  
South West ◽  
South West Monsoon ◽  
West Monsoon

scholarly journals The Barbados Cloud Observatory: Anchoring Investigations of Clouds and Circulation on the Edge of the ITCZ

2016 ◽  
Vol 97 (5) ◽  
pp. 787-801 ◽  
Author(s):  
Bjorn Stevens ◽  
David Farrell ◽  
Lutz Hirsch ◽  
Friedhelm Jansen ◽  
Louise Nuijens ◽  
...  
Keyword(s):  
Climate Change ◽  
Deep Convection ◽  
Seasonal Migration ◽  
Saharan Dust ◽  
Boreal Summer ◽  
Max Planck ◽  
Research Aircraft ◽  
Meteorological Impact ◽  
The Tropics ◽  
The Relationship

Abstract Clouds over the ocean, particularly throughout the tropics, are poorly understood and drive much of the uncertainty in model-based projections of climate change. In early 2010, the Max Planck Institute for Meteorology and the Caribbean Institute for Meteorology and Hydrology established the Barbados Cloud Observatory (BCO) on the windward edge of Barbados. At 13°N the BCO samples the seasonal migration of the intertropical convergence zone (ITCZ), from the well-developed winter trades dominated by shallow cumulus to the transition to deep convection as the ITCZ migrates northward during boreal summer. The BCO is also well situated to observe the remote meteorological impact of Saharan dust and biomass burning. In its first six years of operation, and through complementary intensive observing periods using the German High Altitude and Long Range Research Aircraft (HALO), the BCO has become a cornerstone of efforts to understand the relationship between cloudiness, circulation, and climate change.

scholarly journals Implication of tropical lower stratospheric cooling in recent trends in tropical circulation and deep convective activity

2019 ◽  
Vol 19 (4) ◽  
pp. 2655-2669 ◽  
Author(s):  
Kunihiko Kodera ◽  
Nawo Eguchi ◽  
Rei Ueyama ◽  
Yuhji Kuroda ◽  
Chiaki Kobayashi ◽  
...  
Keyword(s):  
Deep Convection ◽  
Equatorial Indian Ocean ◽  
Boreal Summer ◽  
Convective Activity ◽  
Tropical Circulation ◽  
Surface Cooling ◽  
Central Pacific ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Stratospheric Cooling

Abstract. Large changes in tropical circulation from the mid-to-late 1990s to the present, in particular changes related to the summer monsoon and cooling of the sea surface in the equatorial eastern Pacific, are noted. The cause of such recent decadal variations in the tropics was studied using a meteorological reanalysis dataset. Cooling of the equatorial southeastern Pacific Ocean occurred in association with enhanced cross-equatorial southerlies that were associated with a strengthening of the deep ascending branch of the boreal summer Hadley circulation over the continental sector connected to stratospheric circulation. From boreal summer to winter, the anomalous convective activity center moves southward following the seasonal march to the equatorial Indian Ocean–Maritime Continent region, which strengthens the surface easterlies over the equatorial central Pacific. Accordingly, ocean surface cooling extends over the equatorial central Pacific. We suggest that the fundamental cause of the recent decadal change in the tropical troposphere and the ocean is a poleward shift of convective activity that resulted from a strengthening of extreme deep convection penetrating into the tropical tropopause layer, particularly over the African and Asian continents and adjacent oceans. We conjecture that the increase in extreme deep convection is produced by a combination of land surface warming due to increased CO2 and a reduction of static stability in the tropical tropopause layer due to tropical stratospheric cooling.

scholarly journals The Origin of the South-west Monsoon

Nature ◽  
1921 ◽  
Vol 107 (2683) ◽  
pp. 154-154 ◽  
Author(s):  
G. C. SIMPSON
Keyword(s):  
The South ◽  
South West ◽  
South West Monsoon ◽  
West Monsoon
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