Developing versus non-developing disturbances for tropical cyclone formations. Part II: western North Pacific

This is the second part of the investigation into developing and nondeveloping disturbances over tropical oceans. In this part, we focused on western North Pacific.

The genesis of tropical cyclones depends on atmospheric circulations with a wide range of scales both in time and in space. While cyclonic disturbances exist all the time in the tropics, only a small percentage of them became tropical cyclones. Due to recent improvements of numerical models, data assimilation techniques and applications of remotely-sensed data, global analysis can provides us much more reliable representation of the atmosphere than before. In this study, the daily analysis from the U. S. Navy Operation Global Atmosphere Prediction System (NOGAPS) and TRMM TMI data are analyzed to understand why some disturbances formed tropical cyclones while others did not. The data cover the period of 2003 to 2005 and a time filtering technique is applied to separate circulations with different time/spatial scale.

Tropical cyclone genesis in western North Pacific differs from north Atlantic in both large scale background environmental conditions as well as disturbances sources. Large scale low level convergence and horizontal shear have more impacts on whether or not a disturbance will develop to a tropical cyclone. The nature that tropical cyclone genesis involves multi-scale interactions is examined and contributions from different scales will be presented.