**Author details**

Although the calculation errors in the WRF global model simulation grew significantly after seven days of model integration, it seems that the global WRF can be used for the purpose of operational short‐range TCG forecasting. This result is encouraging, considering the fact that the global WRF model was initialized 42 hours before the simulated TCG and subsequent development of a TC, and yet the forecast will be fairly accurate in one continuous simulation for the 7‐day period. It should be also noted that the 7‐day global WRF model simulation

Planetary‐scale atmospheric and oceanic conditions of the western Atlantic basin were analyzed to understand the unique TCG and intensification mechanism of Hurricane Wilma in 2005, using NCEP/NCAR reanalysis data, NOAA optimum interpolation (OI) ¼ degree daily SST V2 data, NOAA/OAR/ESRL PSD interpolated OLR data, and global WRF model simulation. An anomalous development of the 850 hPa circulation pattern in the North Atlantic was triggered by Hurricane Vince (October 8–11, 2005) in the eastern North Atlantic. Circula‐ tion around the southeastern fringe of the North Atlantic subtropical anticyclone during the period had been interrupted by the presence of Vince, causing a perturbation in the down‐ stream flow around the entire southern edge of the North Atlantic subtropical high. On the southwestern flank of the subtropical high, the perturbation contributed to the development of a large‐scale 850 hPa vortex, which would eventually allow for Wilma's TCG in the eastern Caribbean Sea. Due to the change in the low‐level circulation by the deformed subtropical anticyclone, weakened low‐level easterly winds allowed southeasterly winds from the Southern Hemisphere and westerly winds from eastern North Pacific to become relatively important, generating an anomalously prominent low‐level cyclone over the western Atlantic

The anomalously large low‐level cyclone over the western Atlantic matured over the warm ocean before it was separated into two cyclones in a north‐south alignment (a northern cyclone and a southern cyclone). The separation was caused by the advance of northerly winds from a mid‐latitude trough over central Canada one day before TCG. By 1200 UTC October 15, the high‐latitude trough merged with the northern cyclone, resulting in a strengthened northern subtropical low. The enhanced subtropical low eventually played a role in sustaining the low‐ level circulation in the Caribbean Sea by preventing a significant interference from the zonally propagating tropical waves (**Figure 2c** and **d**). The southern cyclone became more concentrated in the Caribbean Sea, near Jamaica by October 14, growing into a tropical depression by 1800

The unusual but persistent meridionally oriented circulation conditions allowed the tropical depression over the Caribbean Sea to strengthen slowly between the northerly winds associ‐ ated with the trough in the northeastern US and the southeasterly winds from the South Atlantic (**Figure 2c** and **d**). Wilma became a tropical storm at 0600 UTC October 17. Over October 17–18, as the North Atlantic subtropical high strengthened to produce more vigorous

required less than six hours in a Linux cluster computer with 96 cores.

106 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**5. Summary and conclusion**

about a week before TCG.

UTC October 15.

Jinwoong Yoo1\*, Robert V. Rohli2 and Jennifer Collins3

\*Address all correspondence to: jinwoong.yoo@gmail.com

1 The Purdue Climate Change Research Center, Purdue University, West Lafayette, IN, USA

2 Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA, USA

3 School of Geosciences, University of South Florida, Tampa, FL, USA

#### **References**


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#### **Mesoscale Convective Systems and Early Development of Tropical Cyclones Mesoscale Convective Systems and Early Development of Tropical Cyclones**

Kevin K. W. Cheung and Guoping Zhang Kevin K. W. Cheung and Guoping Zhang

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64185

#### **Abstract**

This chapter studies two Tropical cyclone (TC) cases, Typhoon Dan (1999) and Typhoon Ketsana (2003), and discusses their rates of formation and relationship with the mesoscale convective activities through examining the numerical simulations of the two cases. Many TCs generate from a single mesoscale convective System (MCS) or multiple MCSs; the physical processes under these two patterns are found to include dissipation of convection leading to new eruptions of deep convection located near the edge of the dissipating convection core, ingestion of nearby convection, merging of multiple MCSs into one MCS, and merging of deep convection within the MCS associated with the aggregation of vorticity in early development stage of TCs. How these activities lead to the formation of Typhoon Ketsana has been diagnosed. The diabatic heating associated with these convective activities also help to form the TC warm core. The relationship between the rate of TC formation and early development and convection energy consumption is discussed.

**Keywords:** tropical cyclone formation, mesoscale convective systems, stratiform and convective rain, diabatic heating, convective available potential energy

#### **1. Introduction**

Over the recent decades, researches for the process that generates a surface vortex have focused on the observation that TC formation is associated with mesoscale convective systems (MCSs) and their accompanying mesoscale convective vortices (MCVs). It was believed that the transition from MCS to a TC-like vortex required the generation of low-level cyclonic vorticity below the MCS, and researches for TC genesis mechanisms focus on what provided this sub-MCS low-level cyclonic vorticity. It is common to observe MCS or MCSs involved in

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the formation process of TCs in the western North Pacific (WNP). Over 63% of the studied TCs have multiple MCS convection appearing at the formation process, and 35% have the single MCS appearing at the beginning of the formation process. About 90% of cases with a shorter time period of formation process (within 6 h) have single MCS [1]. The physical processes underthe single MCS and multiple MCS convection are found to include dissipation of convection leading to new eruptions of deep convection located near the edge of the dissipating convection core, ingestion of nearby convection, merging of multi-MCSs into single MCS, and merging of deep convection within the MCS associated with the aggregation of vorticity in fast formation process.

An MCS is organized as convective cloud clusters, and TC formation process is due to increasing organizition of MCS, which is caused by accumulation of mesoscale vorticity [2]. Convective activities resulted from thermodynamic and/or dynamic effects that affect the evolution of early development of TCs [3, 4]. They play critical roles in the formation process on TCs; furthermore, the local warming and diabatic heating associated with these convective activities also help to spin up the circulation and generate the warm core structure. How the pattern of MCS convection affects the rate of TC formation and early development is the focus of this chapter. In this chapter, two TC cases are studied and their synopses are first provided before their rates of development are discussed. The model simulations of the two cases are validated in terms of synoptic development and convective episodes. The convection types in the model are separated into convective and stratiform types with their respective vertical heating profiles. Then the heating associated with the MCSs and its effect on TC development are analyzed based on previous theories [5] and through Eliassen–Palm (EP) flux analysis. Then, the rates of development in the two TC cases are discussed based on the convective energy consumption point of view. In regard to this view, convection development and maintenance consume convective available potential energy (CAPE) in their local environment. It gradually makes the local environment less conducive for further convection development, which may affect the temporal evolution of TC formation when the surface vorticity is still below the threshold for tropical storm. However, it humidifies the middle and upper troposphere, and then gradually builds up the value of CAPE again in the local environment until new deep convection bursts up.
