Journal Highlights

Identifying changes in convective air circulation

The Hadley cells form the planetary overturning circulation in the tropical atmosphere. In a Hadley cell, air rises from near the equator at the surface to the upper troposphere, moves poleward until about 30° in latitude, then descends into the subtropics before moving equatorward along the Earth's surface. Recent observations and simulations with climate models suggest that the north-south extent of the Hadley cells may be increasing, which may dramatically alter climate on regional scales. Korty and Schneider (2008) analyzed dynamical mechanisms responsible for terminating the Hadley cells in the subtropics. They suggest that Hadley cells terminate where eddies generated in the extratropics become so deep that they reach the upper troposphere. At the latitude where this occurs, the direction of the momentum flux carried by the eddies changes sign; the tropical Hadley cells give way to the extratropical Ferrel cells. The authors show how the atmospheric thermal structure determines this latitude in dry atmospheres. It remains to be investigated how latent heat release in phase changes of water influences the Hadley cell termination.

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Featured Special Collection

A Census of Atmospheric Variability from Seconds to Decades 

The atmosphere varies naturally on all length scales from millimeters to thousands of kilometers, and on all time scales from seconds to decades and longer.  This special collection of Geophysical Research Letters synthesizes and summarizes that variability through a phenomenological census.  The collection brings together some of the most influential and definitive papers to have been published in this journal in recent years.  The topics covered include turbulence on time scales of seconds and minutes, gravity waves on time scales of hours, weather systems on time scales of days, atmospheric blocking on time scales of weeks, the Madden–Julian Oscillation on time scales of months, the Quasi-Biennial Oscillation and El Niño–Southern Oscillation on time scales of years, and the North Atlantic, Arctic, Antarctic, Pacific Decadal, and Atlantic Multi-decadal Oscillations on time scales of decades.  The collection is accompanied by a Commentary article, which provides an authoritative, concise, and accessible point of reference for the most important modes of atmospheric variability.

A Census of Atmospheric Variability from Seconds to Decades