Geoscience Reference
In-Depth Information
Figure 4.8.
Mean sea level pressure (hPa) for the four mid-season months over the
1970-1999 period, based on NCEP/NCAR data (by the authors).
three troughs and three ridges that is fairly well expressed at about 60°N indicates
that the total circulation at this latitude has a strong wavenumber 3 component. In
summer, the 500 hPa vortex is much weaker in response to the more even latitudinal
distribution of radiation and temperature. It is also more symmetric than its winter
counterpart, with the lowest pressure heights centered over the pole.
4.4.2
Temperature Structure
The annual cycle of temperature in the middle troposphere shows a well-developed
kernlose (or coreless) pattern. This refers to the observation that temperatures at
500 hPa, for example, seldom fall below −45°C in winter, despite a continued net
radiative loss. This characteristic was originally noted in Antarctica. There, the
mechanism seems to be a balance between outgoing longwave radiation, downward
longwave radiation, and sensible heat flux from the top of the surface inversion
