Impact of tropical and subtropical SSTs on mid-latitude tropospheric warming in the northern summer of 2010

Chiaki Kobayashi

doi:10.1007/s00382-013-2013-4

Abstract

The relationship between mid-latitude tropospheric warming (MLTW) and the tropical sea surface temperatures (SSTs) in June–August (JJA) of 2010 has been investigated using an atmospheric general circulation model forced with the evolving observed SSTs. The simulation results indicate that the SST anomalies (SSTAs) in the equatorial Pacific in JJA 2010, indicating La Niña condition, did not contribute simultaneously to produce the MLTW in JJA 2010, and, instead, the SSTAs in the northern subtropics (the whole latitudinal band between 10°N and 30°N) contributed. However, it is shown by the results that enough magnitude of the atmospheric height anomalies over the northern mid-latitude was not reproduced by the SSTAs over the northern subtropical Indo-western Pacific (IWP) alone or over the northern subtropical Atlantic alone. It implies that both the SSTA over the northern subtropics of IWP and Atlantic were necessary to reproduce the MLTW. The possible role of convective activity for the MLTW is also discussed.

Highlights

The northern summer of 2010 was exceptionally warm over a large area of the mid-latitudes in the Northern Hemisphere
The positive anomalies over the North Africa and Middle East are represented in ExIWP (Fig. 7g) and the positive height anomalies over the southern part of North America and the North Atlantic mid-latitude region are produced in ExATL (Fig. 7h). These results suggest that each of the sea surface temperatures (SSTs) anomalies (SSTAs) in the northern subtropics of Indo-western Pacific (IWP) and ATL contribute to produce the mid-latitude tropospheric warming (MLTW) in JJA 2010, enough magnitude of the height anomalies over the northern mid-latitude is not reproduced by the SSTA over the northern subtropical IWP alone or over the northern subtropical Atlantic alone
The simulation results indicated that (1) the SSTAs in the equatorial Pacific (EP) region, indicating La Nina condition, did not contribute simultaneously to produce the MLTW in JJA 2010, (2) the SSTAs over the equatorial area other than EP region contribute to produce the atmospheric warming over the tropical region, (3) the SSTAs in the northern subtropical region work to produce the MLTW, enough magnitude of the anomalies was not reproduced by the SSTAs over the northern subtropical IWP alone or over the northern subtropical Atlantic alone

Summary

Introduction

The northern summer of 2010 was exceptionally warm over a large area of the mid-latitudes in the Northern Hemisphere. The SST anomalies (SSTA) in the NINO3 region (5°N–5°S, 150°W–90°W) was decreasing in March–May (MAM) 2010 and became negative in JJA 2010. The SSTs over the Indo-Western Pacific region indicated slightly warm anomalies and the SSTAs in the tropical Atlantic Ocean were significantly positive in JJA 2010 (Fig. 1d). The Atlantic significant SSTA had peaked in MAM 2010 and persisted from JJA 2009 to JJA 2010 (not shown). The geopotential height at 200 hPa indicate remarkable positive anomalies in the latitudinal bands between 30° and 50° in the both Hemispheres developed in JJA 2010, after positive anomalies in the tropics occurred during the period January to May 2010 in association with the 2009/2010 El Nino conditions

Results

Discussion

Conclusion