Weakening Trend of the Tropical Easterly Jet Stream of the Boreal Summer Monsoon Season 1950–2009

Abish, B.; Joseph, P. V.; Johannessen, Ola M.

doi:10.1175/jcli-d-13-00440.1

Cited by 53 publications

(33 citation statements)

References 16 publications

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“…However, some previous studies have questioned the direct role of tropospheric temperature gradient in changing the monsoon winds [Lindzen and Hou, 1988;Bordoni and Schneider, 2008;Molnar et al, 2010], and it has been shown that a weakened regional Hadley circulation with a southward displaced ascending branch can itself lead to a decrease in monsoon winds without invoking changes in the meridional upper tropospheric temperature gradient and hence a weakened wind shear [Lindzen and Hou, 1988;Bordoni and Schneider, 2008]. In contrast to these studies, Abish et al [2013] have shown that the rapid Indian Ocean warming and the associated convection have warmed the upper troposphere over the central equatorial Indian Ocean and thereby weakened the meridional tropospheric temperature gradient and this has reduced the monsoon winds through the thermal wind balance. However, our discussion on the Indian Ocean warming and associated changes in the regional Hadley circulation and its impact on the MISO propagation are not dependent on any of these arguments.…”

Section: Mechanismsmentioning

confidence: 98%

“…In contrast to these studies, Abish et al . [] have shown that the rapid Indian Ocean warming and the associated convection have warmed the upper troposphere over the central equatorial Indian Ocean and thereby weakened the meridional tropospheric temperature gradient and this has reduced the monsoon winds through the thermal wind balance. However, our discussion on the Indian Ocean warming and associated changes in the regional Hadley circulation and its impact on the MISO propagation are not dependent on any of these arguments.…”

Section: The Agcm Experimentsmentioning

confidence: 99%

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Modulation of monsoon intraseasonal oscillations in the recent warming period

et al. 2014

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The Indian Ocean sea surface temperature (SST) during the boreal summer has shown a significant warming of 0.3°C in the recent decade (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) compared to a former decade (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988), and it is most pronounced in the central tropical Indian Ocean. By using reanalysis and satellite-derived data sets, we investigated how the monsoon intraseasonal oscillation (MISO) over the South Asian summer monsoon (ASM) region has been influenced by the recent warming in the Indian Ocean. It is found that the MISO variance has increased over the ASM region in the recent period compared with the earlier decade. It is also noted that the characteristic northward propagation of the MISO has slowed over 2001-2010, resembling more of a standing oscillation near the equator. Mechanisms implicated in the observed MISO changes are explored by conducting several model sensitivity experiments with an atmospheric general circulation model. The model experiments suggest that the mean SST increase over the Indian Ocean, and the associated changes in the air-sea interaction, the increased mean moisture convergence, and changes in the large-scale circulation are responsible for the changes in the characteristics of the MISO. The influence of the recent Indian Ocean warming on the MISO characteristics must be understood fully since they determine the seasonal amount of rainfall over the Indian subcontinent. An examination of future projections of the MISO using the MPI-ESM-LR model from the Coupled Model Intercomparison Project phase 5 archive also gives consistent result.

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Section: Mechanismsmentioning

confidence: 98%

Section: The Agcm Experimentsmentioning

confidence: 99%

Modulation of monsoon intraseasonal oscillations in the recent warming period

et al. 2014

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“…Another factor could be the weakening of the tropical easterly jet (Koteswaram, ) in the 20th century found by Abish et al . (), resulting in stronger mean zonal winds.…”

Section: Discussionmentioning

confidence: 99%

“…However, Huang et al (2001) suggested that this increase may be due to an intensification of El Niño events or Madden-Julian Oscillations, which would result in stronger westerly winds in the tropical upper troposphere (Lee, 1999). Another factor could be the weakening of the tropical easterly jet (Koteswaram, 1958) in the 20th century found by Abish et al (2013), resulting in stronger mean zonal winds.…”

Section: Trend Analysismentioning

confidence: 99%

Trends in and closure of the atmospheric angular momentum budget in the 20th century in ERA‐20C

Veerman

Heerwaarden

2019

Quart J Royal Meteoro Soc

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It is well known that global warming in the 20th century has influenced the global circulation of the atmosphere. Atmospheric angular momentum (AAM), a measure of the rotation of the atmosphere around the Earth's axis, is a useful quantity to investigate changes in the global atmospheric circulation. In this study, 20th century trends in the AAM budget are determined using the ERA‐20C reanalysis data of the European Centre for Medium‐Range Weather Forecasts (ECMWF). In addition, the closure of the AAM budget is determined to assess the ability of ERA‐20C to conserve angular momentum. The total AAM has increased in the 20th century, associated mainly with an increasing relative (zonal wind) AAM in most of the stratosphere and the tropical upper troposphere, and a poleward redistribution in the midlatitudes. These trends can be related to the warming in the troposphere and cooling in the lower stratosphere found in this study, likely caused by increasing atmospheric CO2 concentrations. The Ω‐AAM, representing the rotation of the atmosphere along with the Earth, shows no clear trend, but a spurious peak around 1920. This peak is caused by a global increase in surface pressure and is considered an artefact of changes in the amount of assimilated observations. It is also found that the AAM budget is not well closed in ERA‐20C, which is mainly the result of the assimilation of observations during production of the reanalysis. The trends in the AAM budget in ERA‐20C are likely affected by changes in the number of assimilated observations and should be validated with other reanalyses in further research.

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“…For example, studies have shown a weakening of MLLJ in recent decades (Joseph and Simon, 2005;Krishnan et al, 2013). Recent studies show a poleward shift in MLLJ (Sandeep and Ajayamohan, 2015), weakening of TEJ (Abish et al, 2013) and strengthening of subtropical jet stream (Abish et al, 2015). The Intergovernmental Panel on Climate Change (IPCC) (2007) on the basis of results from general circulation models has shown that daily heavy rainfall events in many regions around the globe show an increasing tendency.…”

Section: Introductionmentioning

confidence: 99%

The role of monsoon low‐level jet in modulating heavy rainfall events

Xavier

Kottayil

Mohanakumar

et al. 2017

Intl Journal of Climatology

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Monsoon low‐level jet (MLLJ) is an important component of Asian summer monsoon circulation, which is responsible for large‐scale distribution and variability of rainfall over the Indian subcontinent. The evolution of MLLJ characteristics prior to heavy rainfall days and its changes which lead to instances of heavy rainfall over the south‐western coast of India are studied. The European Centre for Medium Range Weather Forecasts (ECMWF) re‐analysis data and India Meteorological Department (IMD) rainfall data during 1979–2007 were used for this study. It is found that the MLLJ core speed, westerly wind depth, zonal water vapour flux, horizontal wind shear and cyclonic vorticity show a steady increase towards the day of heavy rainfall and gradually decrease thereafter. The intensification of these parameters not only brings in abundant moisture but also triggers convection, thereby resulting in the formation of heavy rainfall during monsoon season. The large‐scale advection of moisture brought about by strengthening of MLLJ is shown to be a prerequisite for heavy rainfall over the Indian subcontinent. An interesting result of this study is that heavy rainfall days may have some predictability by continuous monitoring of the progression of MLLJ.

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Weakening Trend of the Tropical Easterly Jet Stream of the Boreal Summer Monsoon Season 1950–2009

Cited by 53 publications

References 16 publications

Modulation of monsoon intraseasonal oscillations in the recent warming period

Modulation of monsoon intraseasonal oscillations in the recent warming period

Trends in and closure of the atmospheric angular momentum budget in the 20th century in ERA‐20C

The role of monsoon low‐level jet in modulating heavy rainfall events

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