Understanding the Predictability of East Asian Summer Monsoon from the Reproduction of Land–Sea Thermal Contrast Change in AMIP-Type Simulation

Abstract

Previous studies on the predictability of East Asian summer monsoon circulation based on SST-constrained Atmospheric Model Intercomparison Project (AMIP)-type simulations show that this phenomenon is reproduced with lower skill than other monsoon patterns. The authors examine the reason in terms of the predictability of land-sea thermal contrast change. In the observation, a stronger monsoon circulation is dominated by a tropospheric warming over East Asian continent and a cooling over the tropical western Pacific and North Pacific, indicating an enhancement of the summertime ''warmer land-colder ocean'' mean state. The tropospheric cooling over the tropical western Pacific and North Pacific, and the tropospheric warming over East Asian continent are reproducible in AMIP-type simulations, although there are biases over both the North Pacific and East Asia. The tropospheric temperature responses in the model indicate a reasonable predictability of the meridional land-sea thermal contrast; the zonal land-sea thermal contrast change is also predictable but shows bias over the region north to 258N in North Pacific. The reproducibility of the meridional thermal contrast is higher than that of the zonal thermal contrast. An examination of the predictability of two commonly used monsoon indices reveals far different skills. The index defined as zonal wind shear between 850 and 200 hPa averaged over East Asia is highly predictable. The skill comes from the predictability of the meridional land-sea thermal contrast. Although the zonal thermal contrast change is mostly predictable except for the biases over the North Pacific, the monsoon index defined as zonal sea level pressure (SLP) difference across the East Asian continent and the North Pacific is unpredictable. The low skill is related to the index definition, which attaches more importance to the land SLP change. The limitation of the index in measuring the land SLP change reduces the model skill. Although regional features of monsoon precipitation changes remain a challenge for current climate models, the predictable land-sea thermal contrast change sheds light on monsoon circulation prediction.

Lagged response of summer precipitation to insolation forcing on the northeastern Tibetan Plateau during the Holocene

“…That is, anomalously warm northwestern Pacific SSTs would have decreased the meridional thermal contrast between East Asia and the tropical western Pacific. This meridional thermal contrast is suggested to be the cause of the EASM (Zhou and Zou 2010), which induces easterly wind anomalies over East Asia transporting water vapour from the northwestern Pacific to the northeastern Tibetan Plateau (Fig. 9b).…”

The strengthening East Asia summer monsoon since the early 1990s

“…The monsoon is determined by land-sea thermal contrast [5,33], which can be expressed by low-level air temperature, sea-level pressure (SLP), and other factors [5]. The land-sea thermal contrast change between 1991-2011 and 1981-1990 is shown in Figure 7(b).…”

Sub-seasonal Predictability of the Onset and Demise of the Rainy Season over Monsoonal Regions

“…The most successful deterministic predictions of monsoon systems to date consist of predicting the large-scale component of the flow, defined as the primary modes of variability (Zhou and Zou, 2010;Zuo et al, 2013;Wang et al, 2015). However, regional features of monsoon precipitation anomalies remain highly unpredictable (Zhou and Zou, 2010).…”