CLIMATE RESEARCH GROUP

Atmospheric circulation and climate change

Major wind and pressure systems throughout the global atmosphere have undergone significant shifts during recent decades. For example, the edges of the tropical Hadley cell have been moving towards the poles by a few degrees over the past 30 years, or in other words, the tropics have been expanding at the expense of the extratropics. At the same time, the extratropics have also undergone important circulation change, as manifested by a poleward shift of the zone of high westerly winds in the midlatitudes, which is also known as an enhanced positive phase of the annular modes (AMs). These circulation trends are important indicators of climate change and are likely to have profound influences on ecosystems and societies.

Climatological mean circulation in the height-latitude plane during boreal summer (JJA). Vertical axis is atmospheric pressure (in hPa) and height (in km) and horizontal axis is latitude (in degrees). The continuous black line denotes the thermally defined tropopause. (left) Zonal mean zonal winds (in m/s) derived from NCEP/NCAR reanalysis. SJ indicates the two subtropical jet cores, and EJ denotes approximate position of the eddy-driven jet. (right) Mean meridional mass streamfunction (in kg/s), with arrows indicating the direction and strength of the zonal mean overturning associated with the Hadley cell, with a strong winter cell in the SH and a weak summer cell in the NH. Adapted from Reichler (2009).

Our research project is targeted towards understanding how climate change affects the strength and structure of the general circulation of the atmosphere and what the driving mechanisms behind these shifts are. To this end, we analyze climate model data, reanalyses, and modern satellite-derived temperature measurements of the atmosphere (e.g., Microwave Sounding Unit MSU, Global Positioning System Radio Occultation GPS-RO, and compare the results with theoretical findings.

Further reading

Reichler, T. (2009): Changes in the atmospheric circulation as indicator of climate change, in: Climate and global change: Observed impacts on planet Earth, T. Letcher, Ed., Elsevier, New York, (in press). [PDF]

Seidel, D., Q. Fu, W. Randel, and T. Reichler (2008): Widening of the tropical belt in a changing climate, Nature Geosci., 1, 21-24. [PDF]


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