Tropical cyclones (TCs) are of the most extreme and dangerous weather phenomena on Earth. In the United States, landfalling TCs account for an average of $10 billion damages annually (Pielke et al. 2008). Hurricane Katrina (2005) alone caused $81 billion of damages and took more than 1,800 lives away. In developing countries, TC landfalls can be extremely detrimental. For example, Cyclone Nargis (2008) took more than 130,000 lives in Myanmer (Burma) . Due to the catastrophic nature of TCs, substantial efforts have been devoted to short-term predictions of TC track and intensity in an effort to minimize the damages and casualties.
In recent years, the relationship between TC activity and climate change has attracted strong attentions in the atmospheric research community. There are a number of evidences suggesting that regional TC activity is going under a substantial shift, which may be a response to changing climate. As discussed later in the chapter, however, detection and association of shifts in TC activity resulting from climate change have been controversial due to uncertainties in the observed data and the difficulty in separating natural variability and anthropogenic forcing. Projections of the future TC activity are also not unanimous; the sources of uncertainties are still being identified and tested for their relative effects in relation to the unanimous projections of TC activity. However, the need for reliable projections for the near-term future TC activities is strong among the governmental organizations and industries located near the coastlines that are often affected by TC landfalls. Therefore, identifying the source of uncertainties in the future projections of TC activity and developing a mechanism to reduce the uncertainties are of the most imperative tasks at hand.
The ultimate goal of this work is to project the future change of North Atlantic TC activity with increasing greenhouse gases using the Nested Regional Climate Model (NRCM, Holland et al. 2010). Substantial attentions will be given to identifying inherent limitations and uncertainties. Approaches will be proposed on how one may reduce some of the limitations and uncertainties. Before proceeding to the actual analysis of the model simulations, it is useful to review the current understanding of the TC-climate relationships, detection and attribution of shifts in the observed TC records, and the model projections of the future TC activity by past studies; and they are outlined in this chapter. This chapter concludes an outline of the thesis.
Researches in the general area of TC and climate relationship have a long history.
A pioneering work by Gray (1968) presented the characteristics of large-scale environment in which TC formations tend to occur; namely high sea surface temperature (SST), high low-tropospheric moisture, background large-scale vorticity, inertial instability, and low vertical wind shear. Although the discovery of these factors is based...