The Atmospheric Response to Time-dependent Tropical Heating, as Estimated from the Fluctuation Dissipation Theorem

Grant Branstator
National Center for Atmospheric Research (NCAR)

Recent studies have demonstrated the applicability of the Fluctuation Dissipation Theorem to atmospheric response problems in which the external stimulus is a function of space but is constant in time. These investigations have made clear the utility of the resulting response operators for addressing questions concerning optimal response, climate control, attribution and physical mechanisms. In this presentation we explore the usefulness of the FDT methodology for response problems in which the imposed forcing is a function of time. In our study we concentrate on the effects of time varying tropical heating. First we valid operators designed to match the solutions of AGCMs. Next we use the operators to systematically explore how the midlatitude response depends on attributes of the tropical heating including its position, structure and movement. Not only are operators for the response of mean state variables considered but also operators that give the response of storm track and precipitation characteristics. This part of the study is followed by application of the theorem to reanalysis data. The resulting operators are not as accurate as those based on AGCM behavior but they are skillful enough to learn about the midlatitude effects of prominent tropical phenomena including the MJO and to determine the consequence of misrepresentation of these features in weather and climate forecasts.

Presentation (PDF File)

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