Open AccessAn analysis of the multiscale nature of tropical cyclone activities in June 2004: Climate background
Author(s) -
Ching Lin,
Sui ChungHsiung,
Yang MingJen
Publication year - 2010
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jd013803
Subject(s) - tropical cyclone , climatology , tropical cyclone scales , environmental science , meteorology , geography , cyclone (programming language) , geology , computer science , field programmable gate array , computer hardware
A record‐breaking five tropical cyclones (TCs) formed in June 2004 in the western North Pacific (WNP), where June is normally a transition month to the typhoon season and therefore sensitive to climate oscillations. This special month (June 2004) was an unusual period in the developing stage of a warm (El Niño) episode and a strong convective phase of the Madden‐Julian Oscillation (MJO). Such climate background is shown to provide large‐scale favorable circulations for TC formation: the warm sea surface temperature anomalies (SSTAs) associated with developing El Niño and convective heating of the MJO to jointly induce weaker easterly trade winds and a large‐scale cyclonic circulation anomaly in the WNP. A space‐time filtering of the outgoing longwave radiation (OLR) and 850 hPa wind fields is performed to identify the MJO, Rossby waves, and mixed Rossby‐gravity (MRG) waves (or tropical depression (TD)‐type disturbances). From the evolution and structure of these high‐frequency waves in relation to that of the MJO and the climate background, the heating and enhanced low‐level cyclonic flow in the WNP associated with the MJO and climate background are attributed to the initiation, propagation, and energy dispersion of tropical Rossby and MRG‐TD waves, interacting with convection. The relative importance of these large‐scale waves to the five TC formations (A–E) is quantified by examining the normalized vorticity at 850 hPa and OLR at the genesis location of each TC. TCs A and C (TCs B and D) were related to the Rossby wave (the MJO), and the MRG‐TD was the most related to TC E.