Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part I: North Atlantic

Abstract

This study investigates the characteristic differences of tropical disturbances that eventually develop into tropical cyclones (TCs) versus those that did not, using global daily analysis fields of the Navy Operational Global Atmospheric Prediction System (NOGAPS) from the years 2003 to 2008. Time filtering is applied to the data to extract tropical waves with different frequencies. Waves with a 3-8-day period represent the synoptic-scale disturbances that are representatives as precursors of TCs, and waves with periods greater than 20 days represent the large-scale background environmental flow. Composites are made for the developing and nondeveloping synoptic-scale disturbances in a Lagrangian frame following the disturbances. Similarities and differences between them are analyzed to understand the dynamics and thermodynamics of TC genesis. Part I of this study focuses on events in the North Atlantic, while Part II focuses on the western North Pacific.A box difference index (BDI), accounting for both the mean and variability of the individual sample, is introduced to subjectively and quantitatively identify controlling parameters measuring the differences between developing and nondeveloping disturbances. Larger amplitude of the BDI implies a greater possibility to differentiate the difference between two groups. Based on their BDI values, the following parameters are identified as the best predictors for cyclogenesis in the North Atlantic, in the order of importance: 1) water vapor content within 925 and 400 hPa, 2) rain rate, 3) sea surface temperature (SST), 4) 700-hPa maximum relative vorticity, 5) 1000-600-hPa vertical shear, 6) translational speed, and 7) vertically averaged horizontal shear. This list identifies thermodynamic variables as more important controlling parameters than dynamic variables for TC genesis in the North Atlantic. When the east and west (separated by 408W) Atlantic are examined separately, the 925-400-hPa water vapor content remains as the most important parameter for both regions. The SST and maximum vorticity at 700 hPa have higher importance in the east Atlantic, while SST becomes less important and the vertically averaged horizontal shear and horizontal divergence become more important in the west Atlantic.

The influence of large-scale circulations on the extremely inactive tropical cyclone activity in 2010 over the western North Pacific

“…No robust relationship is found between TC number and ENSO, in agreement with previous studies (Chan, 1985;Lander, 1994;Wang and Chan, 2002;Zhao et al, 2010). Further, based on the BDI method proposed by Peng et al (2012), dynamic factors are found to be more important in differentiating the TC formation over the WNP basin between 2010 and 1994. It may be mainly due to the remarkable difference in monsoon flows in the WNP basin between 2010 and 1994.…”

“…Recently, Peng et al (2012) developed the box difference index (BDI) methodology, which can quantitatively determine which parameter at which level is best in distinguishing developing and non-developing disturbance groups. Using the BDI method, the relative importance of environmental factors affecting TC genesis over the WNP basin is assessed, comparing an extreme high TC number for 1994 and an extreme low TC number for 2010.…”

A First Look at the Structure of the Wave Pouch during the 2009 PREDICT–GRIP Dry Runs over the Atlantic

“…They found that the low-level relative vorticity can best discriminate between developing and nondeveloping disturbances. Peng et al (2012) compared developing and nondeveloping disturbances over the North Atlantic and suggested that the vertically integrated moisture, rain rate, 750-hPa relative humidity, and divergence are the most important factors in determining whether or not a tropical disturbance will develop into a tropical storm. Peng et al found also that prior to rapid development into a tropical storm, developing disturbances may not possess stronger vorticity than their nondeveloping counterparts.…”

“…For example, McBride and Zehr (1981) tracked cloud clusters while Kerns and Zipser (2009) tracked vorticity maxima. Peng et al (2012) excluded disturbances with maximum relative cyclonic vorticity less than 10 25 s…”

Precursor synoptic‐scale disturbances associated with tropical cyclogenesis in the South China Sea during 2000–2011

“…In this study, we examined only developing disturbances. A comparison of developing and non-developing disturbances such as observational studies done by Peng et al (2012) and Fu et al (2012) is needed, in order to fully understand cyclogenesis processes over the SCS.…”