Stably Stratified Planetary Boundary Layer Effects in Northern Hemisphere Climate

Esau I., Davy R.

Planetary boundary layers contribute to the shaping and maintaining of the Earth’s climate. The deep penetrative convection and convective adjustment cool the planet and controls the hydrological cycle. Hence, the convective processes are intensively studied by climatologists. By contrast, the shallow stably-stratified boundary layer receives much less attention. Its impact is mostly associated with local climate features. This study demonstrates that the stratified boundary layer has significant impact on the global earth’s climate. The study identifies the stably-stratified boundary layer depth as a leading factor modulating the surface air temperature response to anomalous climate heat balance. Geographically, the regions with the largest surface air temperature trends and variability are collocated with the regions where the shallow stably-stratified boundary layers frequently occur. The linear correlation coefficients between the inverse stably-stratified boundary layer depth and the surface air temperature reach 0.4—0.6 over Eurasia and the Arctic sea ice. Particularly strong correlations are found for the continental climates over Siberia where the impacts of soil moisture and cloudiness are less pronounced. Climate models do not adequately represent the depth of the stably-stratified boundary layer which results in systematic model biases both in climate temperature trends and in short-term temperature variability.

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