Intraseasonal relationships between tropical heating and extratropical jets

Abstract

Intraseasonal variations of the northern midlatitude circulation and their relationships with the global tropical heating field are investigated using climate model fields. The greatest intraseasonal variance in the midlatitude flow is found in the vicinity of the time mean jets, and in the areas immediately downstream of these jet exits. The model kinetic energy field associated with these jets shows a clear 30-60 day variation and eastward propagation within and between the different jet regions. This intraseasonal behavior is found to be well correlated with heating anomalies in specific parts of the global tropics. For each of the jet regions, we use a simple composite analysis to identify the global heating patterns associated with periods of strong and weak flow. For the North Pacific jet, strong flow occurs during and after periods of positive heating anomalies in the tropical western and central Pacific, and negative heating anomalies in the Indian Ocean. Conversely, the North Pacific flow is weak when these heating anomalies are reversed. The North Atlantic jet shows comparable relationships, with positive heating anomalies in the tropical western and eastern Pacific, and negative heating anomalies in the tropical Indian and Atlantic Oceans, before and during periods of strong flow.