Intensification of the South Side of the Asian Jet Stream during the Northern Winter in CMIP5 models

Abstract

The winter response of the Asian jet stream to global warming is investigated using the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model dataset under the RCP4.5 scenario. We first evaluate model performances in reproducing the current climatology in the upper troposphere and select the best 27 models. A multi-model ensemble projection by the selected models indicates that the jet stream over the Indochina peninsula and the South China Sea is intensified on its equatorial side in the late 21st century, while the jet stream shifts poleward over the Eurasian continent and the North Pacific. The strengthening of the jet stream on the south side is associated with cyclonic (anticyclonic) circulation anomalies in the upper (lower) troposphere over the southern part of China and decreased upper tropospheric divergence over the Maritime Continent. The strength of the upper tropospheric divergence and the amplitude of the anticylonic eddy streamfunction are strongly correlated. These findings suggest that future changes in the jet stream are related to the weakening of a Matsuno-Gill response to tropical heating.(Citation: Harada, M., S. Hirahara, S. Hagiya, H. Murai, Y. Oikawa, and S. Maeda, 2013: Intensification of the south side of the Asian jet stream during the northern winter in CMIP5 models. SOLA, 9, 94−97,

Impacts of Slowed Tropical Circulation on Winter Stationary Waves in East Asia and the North Pacific

“…These results are the same as Harada et al (2013, their figure 3), but for a bigger region. At low latitudes, changes in the eddy streamfunctions display a baroclinic structure; a cyclonic (anticyclonic) response in the upper (lower) troposphere is located to the northwest and southwest of decreased divergence over the Maritime Continent (Fig.…”

“…1c). Harada et al (2013) showed that the changes in the streamfunctions were associated with weakening of the Matsuno-Gill response (Matsuno 1966;Gill 1980). In contrast, at mid and high latitudes, the changes in the streamfunctions have equivalent barotropic structures and show a wave-like pattern from low to high latitudes.…”

“…Following Harada et al (2013), 27 CMIP5 models, which exhibit good reproducibility of the tropical circulation, are selected (Table 1). We define the present climatology as the average during the late 20th century (1981−2000) from a historical run, and the future climatology as the average in the late 21st century (2081−2100) based on the RCP4.5 scenario.…”

“…In Section 2, we explain the dataset and the settings of the LBM experiments. In Section 3, we outline the future changes in stationary waves previously reported by Harada et al (2013). We present the results of the LBM experiments in Section 4.…”

“…Using Coupled Model Intercomparison Project Phase 3 (CMIP3) models with the SRES A1B scenario, Hori and Ueda (2006) suggested that poleward shifts of the subtropical jet stream and the Aleutian low would be associated with expansion of the local Hadley cell due to the weakening of the tropical circulation. Harada et al (2013) analyzed CMIP5 models under the RCP4.5 scenario and showed that intensification of the subtropical jet stream over the Indochina Peninsula would be caused by weakening of the Matsuno-Gill pattern (Matsuno 1966;Gill 1980) in response to a slowed Walker circulation (Held and Soden 2006;Vecchi and Soden 2007). They also suggested that changes in the planetary wave near Japan (Kimoto 2005) might be due to changes in Rossby wave propagation from low to high latitudes.…”