On the intra-seasonal to decadal climate variability over South-Asia
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
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.
South Asia, monsoon, western disturbances, fog, climate variability, climate dynamics, teleconnections, ENSO, NAO, CGT
Meteorology and Atmospheric Sciences
Research subject Atmospheric Sciences and Oceanography
IdentifiersURN: urn:nbn:se:su:diva-62988ISBN: 978-91-7447-375-9OAI: oai:DiVA.org:su-62988DiVA: diva2:446306
2011-11-18, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Shukla, Jagadish, Professor
Körnich, Heiner, Assistant ProfessorKjellström, Erik, Associate Professor
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted. 2011-10-272011-10-062011-10-13Bibliographically approved
List of papers