Temperature Trend Patterns in Southern Hemisphere High Latitudes: Novel Indicators of Stratospheric Change

Abstract

Robust stratospheric temperature trend patterns are suggested in the winter and spring seasons in the Southern Hemisphere high latitudes from the satellite-borne Microwave Sounding Unit (MSU) measurement for 1979–2007. These patterns serve as indicators of key processes governing temperature and ozone changes in the Antarctic. The observed patterns are characterized by cooling and warming regions of comparable magnitudes, with the strongest local trends occurring in September and October. In September, ozone depletion induces radiative cooling, and strengthening of the Brewer–Dobson circulation (BDC) induces dynamical warming. Because the trends induced by these two processes are centered in different locations in September, they do not cancel each other, but rather produce a wavelike structure. In contrast, during October, the ozone-induced radiative cooling and the BDC-induced warming exhibit a more zonally symmetric structure than in September, and hence largely cancel each other. However, the October quasi-stationary planetary wavenumber 1 has shifted eastward from 1979 to 2007, producing a zonal wavenumber-1 trend structure, which dominates the observed temperature trend pattern. Simulated temperature changes for 1979–2007 from coupled atmosphere–ocean general circulation model (AOGCM) experiments run for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) are compared with the observations. In general, the simulated temperature changes are dominated by zonally symmetric ozone-induced radiative cooling. The models fail to simulate the warming in the southern polar stratosphere, implying a lack of the BDC strengthening in these models. They also fail to simulate the quasi-stationary planetary wave changes observed in October and November.

On the seasonal dependence of tropical lower-stratospheric temperature trends

“…The derived dynamic trends based on the two reanalyses agree very well in the NH while the differences are significant in the SH. The close agreement between the NCEP/NCAR reanalysis and the MSU observations in the SH high latitudes in terms of stratospheric temperature trend patterns (Hu and Fu, 2009;Lin et al, 2009) lends confidence to the NCEP/NCAR reanalysis eddy heat flux trend in SH. Furthermore the derived SH dynamic trends based on the independent analysis that does not use the reanalysis data agree with those using the NCEP/NCAR reanalysis .…”

“…Observational evidence of an accelerated BDC has been shown over both the tropics (e.g., Rosenlof and Reid, 2008;Thompson and Solomon, 2009) and high latitudes (Johanson and Fu, 2007;Hu and Fu, 2009;Lin et al, 2009 …”

Stratospheric warming in Southern Hemisphere high latitudes since 1979

“…Butchart and Scaife (2001) and Butchart et al (2006) also showed intensification of the Brewer-Dobson circulation in full atmospheric GCM simulations forced by both increasing greenhouse gases and time-varying SSTs. However, coupled atmosphere-ocean GCM simulations for the Intergovernmental Panel on Climate Change Fourth Assessment Report failed to reproduce the observed high-latitude stratospheric warming, as pointed out by Lin et al (2009). In addition, El Nino and Southern Oscillation may also contribute to the interannual variability of the observed temperatures, which needs to be considered in future studies.…”

“…This weak increase can hardly explain the strong warming in October and its eastward shifting. In a very recent work by Lin et al (2009), they showed that the eastward shifting of warming trend pattern between September and October is due to a phase shift of climatological-mean center of high temperatures in the SH stratosphere in October in the past few decades. They found that the effect of the phase shift can Increasing wave fluxes in the middle and high-latitude stratosphere would also cause more ozone to be transported from low to high latitudes (Fusco and Salby, 1999;Fischer et al, 2008).…”

Radiative and dynamical contributions to past and future Arctic stratospheric temperature trends

“…However, in the lower stratosphere (15-20 km) Thompson et al (2012) show good agreement between various satellite and radiosonde data sets, although most climate and chemistry-climate models underestimate the degree of this cooling. Lin et al (2009) conclude that IPCC AR4 models fail to simulate the BDC strengthening in the southern polar stratosphere. In addition there are significant differences between measurements of mean age of air and CCM simulations (Ray et al, 2010).…”