Joint Seminar: Interannual Modulations of the East Asian Winter Monsoon under the Remote Influence from the Tropics and Arctic

The East Asian winter monsoon is a near-surface manifestation of planetary waves and modulated intra- seasonally and interannually in association with the anomalous surface Siberian High (SH) and/or Aleutian Low (AL). The Western Pacific (WP) pattern, characterized by north-south dipolar anomalies in pressure, may be regarded as a preferred mode of variability that modulates the monsoon by changing the SH and AL. In fact, the dipolar anomalies in baroclinic structure can convert available potential energy from the climatological-mean field. The conversion is more efficient than the net feedback forcing by sub-weekly transients and sufficient for maintaining the monthly WP pattern. The pattern can thus be modulated by any external forcing. Enhanced convective activity over the South China Sea during a La Niña event is known to favor the blocking phase of the WP pattern. We have revealed that the activity of the Australian summer monsoon is uncorrelated with tropical SST variability and remotely modulates the WP pattern with its blocking phase triggered more preferentially under the enhanced monsoon. The SH intensity is found to be modulated also by sea-ice variability in the Barents/Kara Seas (BKS). We have revealed that enhanced heat release in the BKS under reduced ice cover acts to generate a blocking ridge around the Urals and strengthen the SH by inducing anomalous surface cold advection into central Eurasia, contributing to a recent trend toward the Warm Arctic/Cold Eurasian (WACE) pattern. AGCMs tend to underestimate the WACE response to the reduced BKS ice cover and the degree of this underestimation varies considerably from one model to another.

Datum

03.12.2019

Uhrzeit

15:15 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Hisashi Nakamura, University of Tokyo

Chair

Daniela Matei

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