More On The Arctic; Have The Coldest Temperatures In The Mid-Troposphere Warmed?

In the July 15th blog, the issue of Arctic sea ice melting was discussed. The issue of tropospheric temperature trends has also been investigated. In two papers (see Chase et al., 2002: A proposed mechanism for the regulation of minimum midtropospheric temperatures in the Arctic. J. Geophys. Res., 107(D14), 10.10291/2001JD001425 and Tsukernik et al., 2004: On the regulation of minimum mid-tropospheric temperatures in the Arctic. Geophys. Res. Lett., 31, L06112, doi:10.1029/2003GL018831), we investigated whether the area coverage of the coldest temperatures at 500 mb (which is in the mid-troposphere) in the Northern Hemisphere winter has decreased between 1950 and 1998 (it had not as shown in the first of these two papers; see Figure 1 in that paper).

The motivation of this study was a discussion in front of 500 mb weather maps by Professor Ben Herman and me during my visit at the University of Arizona. We both had noted that the coldest temperatures (-40°C to -45°C) were typically reached in November, rather than continuing to become colder for the rest of the winter. We found there is a feedback between the ocean sea surface temperatures and the temperatures at 500 mb. Even though the air at 500 mb could become colder for short times over large continental areas such as Siberia, the air is advected often enough over ice-free ocean (but near freezing) that cumulus convective mixing results in a vertical temperature lapse rate that is nearly moist adiabatic. This produces 500 mb temperatures that are close to -45°C.

This self-regulation of the climate system indicates that the Arctic troposphere, in terms of the areal average of the coldest mid-tropospheric temperatures, is more resilient to change than expressed in the Arctic Climate Impact Assessment (ACIA) report. This is another set of peer-reviewed papers that was ignored in the ACIA study.

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