One of the great remaining unanswered questions in tropical meteorology is why there are 90 tropical cyclones (TCs) globally, on average, per year as opposed to 10, 1000, or 10000 TCs. In contrast to extratropical cyclones whose annual frequency can be roughly calculated given the large scale characteristics of the mid-latitudes, there is no equivalent theory that even justifies the order of magnitude of TCs that occur globally each year. In spite of this, there appears to be a preferential spacing of approximately 1500-2000 km between TCs during multiple TC episodes in the Eastern North Pacific, North Atlantic, and Western North Pacific possibly suggesting that the number of storms in each basin is limited energetically by the environment. Reconciling these issues is fundamentally rooted in determining the role of TCs within the climate. Building upon previous research (e.g. Sobel and Camargo 2005, Hart et al. 2007), the following study seeks to take a preliminary step in addressing these questions by quantifying the spatiotemporal scales over which TCs and the large scale environment interact. Four-dimensional, storm-relative composites of raw variables, raw anomalies, and normalized anomalies for Western North Pacific TCs are utilized in the analysis presented here.

Preliminary results show that the passage of a TC may be initially responsible for exciting a large scale cooling and drying of the atmospheric environment spanning the majority of the composite domain. Within two weeks, these anomalies are found to become localized over the region in which the TC directly passed through and most strongly manifest themselves as a drying of the lower and middle tropospheric environment. The spatial distribution of the moisture and temperature anomalies in the area immediately surrounding the TC track suggests that the suppression of convection potentially due to the underlying sea surface temperature cold wake induced by the TC is the predominant factor in anomaly maintenance. Furthermore, the periodic pulsation in the magnitude of the dry anomalies, approximately every 10 days following TC passage, either implies the passage of waves generated independently of the TC or in response to the passage of the TC itself that further serve to increase the stabilization of the atmospheric environment. In their totality, these results suggest that TCs serve as an efficient mechanism for regulating atmospheric instability within the tropics for weeks after TC passage.