An overview of the THORPEX-Pacific Asian Regional Campaign (T-PARC) during August-September 2008

The THORPEX Pacific Asian Regional Campaign (T-PARC) during August-September 2008 is a multi-national field campaign that addresses the shorter-range dynamics and forecast skill of one region (Eastern Asian and the western North Pacific) and its downstream impact on the medium-range dynamics and forecast skill of another region (in particular, the eastern North Pacific and North America). While T-PARC encompasses varying time and space scales, the primary objectives of each region are the same: To increase understanding of the mechanisms that will lead to improved predictive skill of high impact weather events. This multi-scale approach of T-PARC is desirable as high impact weather events over these two regions have strong dynamical links. For example, high-impact weather events over the western North Pacific and East Asia, such as persistent deep tropical convection and tropical cyclones, can trigger downstream responses over the eastern North Pacific and North America via upper-tropospheric wave packets on the primary Asian wave guides. These wave packets can, in turn, be invigorated by subsequent cyclogenesis events, which make the impacts farther downstream fast-spreading, far-reaching, and associated with reduced predictability. The high-impact weather events over North American driven by these processes include intense extratropical cyclones, orographic precipitation, flooding, severe weather and the hot, dry winds that increase the risk of wild fires and the severity of droughts.

A combination of observational platforms and collaborative experiments will be utilized to observe the structure and evolution of the primary Asian/North Pacific wave guides high impact events (heavy rainfall, tropical cyclones and extratropical cyclogenesis) that take place over the western North Pacific and East Asian region that interact with these wave guides. Such an ambitious measurement strategy can only be reasonably accomplished with the level of international collaboration envisioned in 2008. A tropical measurement strategy is designed to examine the large-scale variability in the circulation of the tropical western North Pacific as it relates to enhanced and reduced periods of wide-spread deep convection, tropical cyclone formation and the variations in intensity and track as the systems move to the northwest. The measurement strategy for the extratropical transition (ET) and downstream impacts is based on the poleward movement of a decaying tropical cyclone and the resulting intense cyclogenesis that results from its interaction with the midlatitude circulation. The ET process illustrates clearly the need for a tropical-to-extratropical measurement strategy as the predictability of an ET event depends on the intensity and structure of the tropical cyclone, the characteristics of the middle latitude wave guide that impact the ET cyclogenesis, and the downstream propagation and evolution of the wave packets.

These observations will be used in concert with an unprecedented variety of numerical models, which includes research modeling and assimilation systems together with access to the members of the ensemble forecasts of all the major operational centers through the THORPEX Interactive Global Grand Ensemble (TIGGE). Thus, unlike past weather experiments, T-PARC will be able to readily include the probabilistic nature of the forecast problem, rather than examination of a few deterministic forecasts from research and operational models. TIGGE will provide some insight into the initial condition and model errors, while essentially assuring a strong link between the research and operational communities.