Why We Need to Focus on Regional Tropospheric Temperature Trends

In the Climate Science Weblog of July 28, 2005 entitled “What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?“

it was stated that,

“The 2005 National Research Council report concluded that:

‘regional variations in radiative forcing may have important regional and global climate implications that are not resolved by the concept of global mean radiative forcing.’

And furthermore:

‘Regional diabatic heating can cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing.’

This regional diabatic heating produces temperature increases or decreases in the layer-averaged regional troposphere. This necessarily alters the regional pressure fields and thus the wind pattern. This pressure and wind pattern then affects the pressure and wind patterns at large distances from the region of the forcing which we refer to as teleconnections.�

To further communicate the importance of the regional variations in tropospheric temperatures on the weather that we experience, it is useful to refer to the National Center for Environmental Prediction (NCEP) analyses and forecasts where the anomalies in the tropospheric temperatures are analyzed on a daily basis. A particularly effective display of this information is given at a UCAR web site (see RAP , and then click the time period of interest and “500 mb Z-Anomalyâ€?).

The 500 mb Z-Anomaly is dependent on the layer-averaged temperature below the middle troposphere. When the anomaly is below average, the lower troposphere is colder than average, while the lower troposphere is warmer than average when the anomaly is positive.

The assessment of multi-decadal lower tropospheric temperature trends using such anomalies is what we reported on in 2000 in Chase et al: “A comparison of regional trends in 1979-1997 depth-averaged tropospheric temperatures”.

The examination of the NCEP analysis and forecast data shows two main items with respect to the climate:

1. The anomalies are significant in magnitude and are on the regional scale. An average value of the anomalies over the entire analysis grid would be of very little value in terms of weather forecasts.

2. The anomalies almost always have large values of both negative and positive sign. With a warming troposphere we would expect to see a greater predominance of positive anomalies. The assessment in the trends in these regional anomalies should be a high priority for the climate change community.

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