labs_title

Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

Historical trends in the jet streams

Cristina L. Archer & Ken Caldeira

A study of the historical properties of jet streams, fast moving winds located fairly high in the atmosphere whose behavior is an important factor in midlatitude weather. Generally, jet streams were found to have increased in altitude and moved closer to the poles. They weakened and strengthened variously.


Archer, CL; Caldeira, K, 2008. Historical trends in the jet streams, Geophysical Research Letters 35 (8), DOI: 10.1029/2008GL033614.

Averages and trends in jet streams: average (left) jet stream speeds, as well as strengthening and weakening trends (right). Jet streams are generally strongest in the East, and have weakened over time in the Northern Hemisphere and the Sub-Tropical Southern Hempishere.

Jet stream pressure averages and trends: Jet stream pressure was used to measure altitude. Jet streams are generally located between 400 and 100 hPa (hectopascal, 1/1000 of an atmosphere). Over time, an almost across the board reduction in pressure was observed. This reduction in pressure means that jet streams have risen in altitude over time.

Abstract

Jet streams, the meandering bands of fast winds located near the tropopause, are driving factors for weather in the midlatitudes. This is the first study to analyze historical trends of jet stream properties based on the ERA-40 and the NCEP/NCAR reanalysis datasets for the period 1979 to 2001. We defined jet stream properties based on mass and mass flux weighted averages. We found that, in general, the jet streams have risen in altitude and moved poleward in both hemispheres. In the northern hemisphere, the jet stream weakened. In the southern hemisphere, the sub-tropical jet weakened, whereas the polar jet strengthened. Exceptions to this general behavior were found locally and seasonally. Further observations and analysis are needed to confidently attribute the causes of these changes to anthropogenic climate change, natural variability, or some combination of the two.