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Are intraseasonal summer rainfall events micro monsoon onsets over the western edge of the South-Asian monsoon?
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2010 (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 98, no 2-4, 341-346 p.Article in journal (Refereed) Published
Abstract [en]

A thermodynamic structure leading the active phase (AP) of the Western Edge of the South-Asian Monsoon (WESAM) is investigated The APs seems to have significant contribution in the mean seasonal rainfall in the region A few days before APs the upper level warm anomaly appears over the north Hindu Kush-Himalaya (HKH) region and It is reinforced by surface heating yielding the column average warming The height anomalies are baroclinic with the low-level anticyclone being located at the east of warming The low-level anticyclone causes the moisture convergence at the core WESAM region As the region keeps warming, the height anomalies and associated low-level convergence become stronger The AP starts when the low-level moisture convergence is strong enough to overcome the preexisting stable atmospheric condition due to the upper level warming The proposed mechanism of APs has some resemblance with large scale south Asian monsoon onset, whereas conventional south Asian monsoon intraseasonal oscillations (ISOs) do not show clear relationship with APs of WESAM

Place, publisher, year, edition, pages
2010. Vol. 98, no 2-4, 341-346 p.
Keyword [en]
Onset, Pakistan, Intraseasonal variability, Monsoon, Active phases
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-51241DOI: 10.1016/j.atmosres.2010.07.006ISI: 000284983400016OAI: oai:DiVA.org:su-51241DiVA: diva2:387716
Note
authorCount :4Available from: 2011-01-14 Created: 2011-01-10 Last updated: 2017-12-11Bibliographically approved
In thesis
1. On the intra-seasonal to decadal climate variability over South-Asia
Open this publication in new window or tab >>On the intra-seasonal to decadal climate variability over South-Asia
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

South Asia, a land of contrasting landscapes, seasons and climates, is highly vulnerable to climate variability over intra-seasonal to decadal time scales. In winter, precipitation over the western parts of south Asia and fog over the Indo-Gangetic (IG) plains are the two major climatic features. During summer most of the region comes under the grip of monsoon.

Winter precipitation over the north-western parts of South Asia is associated with eastwards propagating ‘western disturbances’ originating mostly from Mediterranean. Both observations and regional climate-model simulations show that the winter precipitation increases/decreases during the positive/negative phases of the North Atlantic Oscillation (NAO) and the warm/cold phase of the El Niño-Southern Oscillation (ENSO). During these phases, the intensification of western disturbances results from the effect of an enhanced trough visible at sea-level as well as at higher altitudes over central Asia. The inter-annual variability of fog is coupled over IG plains with a significant trend in the fog frequencies, both in observations and ERA-Interim reanalysis data. This increase shows two distinct regime shifts in 1990 and 1998 with respect to mean and variance, this in contrast to a gradual increase of the humidity over the region.

The thermodynamic analysis of the intra-seasonal summer monsoon active phases (APs) over Pakistan revealed that a few days before AP, an upper-level warm anomaly appears over the northern Hindu Kush-Himalaya region and is reinforced by surface heating. The baroclinic height anomalies, with a low-level anticyclone located east of the warming, causes a moisture convergence, strong enough to overcome the preexisting stable atmospheric conditions. The extratropical dynamics also play an important role for the inter-annual variation of the South-Asian monsoon. It is found that the two leading modes between the upper-level circulation in the Atlantic/European region and monsoon rainfall are the Circumglobal Teleconnection (CGT) and the summer NAO. The positive phase of the CGT is related to a widespread increase of monsoon rainfall, and a positive summer NAO is related to a precipitation dipole with its positive anomaly over Pakistan.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2011. 30 p.
Keyword
South Asia, monsoon, western disturbances, fog, climate variability, climate dynamics, teleconnections, ENSO, NAO, CGT
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-62988 (URN)978-91-7447-375-9 (ISBN)
Public defence
2011-11-18, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted. Available from: 2011-10-27 Created: 2011-10-06 Last updated: 2011-10-13Bibliographically approved

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