Investigation of Kelvin wave periods during Hai-Tang typhoon using Empirical Mode Decomposition P. Kishore a, * , J. Jayalakshmi b , Pay-Liam Lin b , Isabella Velicogna a, c , Tyler C. Sutterley a , Enrico Ciracì a , Yara Mohajerani a , S. Balaji Kumar b, d a Department of Earth System Science, University of California, Irvine, CA, 92697, USA b Department of Atmospheric Science, College of Earth Sciences, National Central University, Zhongli City, 32001, Taiwan c Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA d Taiwan International Graduate Program (TIGP), Earth System Science (ESS) Program, Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan ARTICLE INFO Keywords: Typhoon-rainfall Empirical mode decomposition (EMD) Kelvin and planetary waves Winds Precipitation ABSTRACT Equatorial Kelvin waves (KWs) are fundamental components of the tropical climate system. In this study, we investigate Kelvin waves (KWs) during the Hai-Tang typhoon of 2005 using Empirical Mode Decomposition (EMD) of regional precipitation, zonal and meridional winds. For the analysis, we use daily precipitation datasets from the Global Precipitation Climatology Project (GPCP) and wind datasets from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-analysis (ERA-Interim). As an additional measurement, we use in-situ precipitation datasets from rain-gauges over the Taiwan region. The maximum accumulated pre- cipitation was approximately 2400 mm during the period July 17–21, 2005 over the southwestern region of Taiwan. The spectral analysis using the wind speed at 950 hPa found in the 2nd, 3rd, and 4th intrinsic mode functions (IMFs) reveals prevailing Kelvin wave periods of ~3 days, ~4–6 days, and ~6–10 days, respectively. From our analysis of precipitation datasets, we found the Kelvin waves oscillated with periods between ~8 and 20 days. 1. Introduction Tropical Cyclones (TC) are the most catastrophic weather phenome- non in Taiwan. While several typhoons occur near and around Taiwan every year, only three or four make landfall in Taiwan. Hai-Tang was a category-5 typhoon with large intensity and coverage, long duration, and intense rainfall. The strong winds and heavy rainfall of these storms often cause catastrophic flooding, mudslides, debris flow, agriculture damage, tremendous loss of property and human lives (Wu and Kuo, 1990; Lee et al., 2006). The creation of TC involves a tropical perturbation that quickly forms into a warm-centre, cyclonic framework with sustainable winds. The timing of TC formation depends crucially on the evolution of the plane- tary waves/disturbances (i.e. the observed qualities of tropical sum- mertime synoptic-scale disturbances or ingrained mesoscale convective frameworks in terms of structure and propagation) preceding the for- mation of individual storm events (Fu et al., 2007). Numerous synoptic-scale patterns have been identified as favorable to tropical cyclogenesis, include but are not limited to: Tropical Upper Tropospheric Troughs (Sadler, 1978), mixed Rossby-gravity waves (Dickinson and Molinari, 2002), and easterly waves (Fu et al., 2007). The generation of a Rossby wave of a TC and the formation of a new clone demonstrated by Li et al. (2003). Planetary waves are global scale atmospheric oscillations with periods of 2–40 days, and originate in the lower troposphere due to large-scale disturbances that are closely coupled with weather systems (Lindzen, 1967). Matsuno (1966) predicted the basic structures of Kelvin waves (KWs), such as, mixed Rossby-gravity waves, east and westward propagating inertia-gravity waves. Kelvin waves are equatorially trapped oscillations, which play a fundamental role in the tropical convective process. Several studies provided observations of Kelvin waves over the Eastern Pacific(Straub and Kiladis, 2002), the Atlantic (Wang and Fu, 2007), Africa (Mounier et al., 2007), the Indian Ocean (Roundy, 2008), and South America (Liebmann et al., 2009). Dunkerton and Baldwin (1995) and Wheeler et al. (2000) both emphasized the existence of these waves with different spectral analysis techniques and filtering methods using satellite and ground-based instruments. A wavelike disturbance was observed using meridional wind fields and low-level vorticity, and this wave propagates north-westward with a * Corresponding author. E-mail address: kishore@uci.edu (P. Kishore). Contents lists available at ScienceDirect Journal of Atmospheric and Solar-Terrestrial Physics journal homepage: www.elsevier.com/locate/jastp http://dx.doi.org/10.1016/j.jastp.2017.07.025 Received 15 April 2017; Received in revised form 13 July 2017; Accepted 27 July 2017 Available online 1 September 2017 1364-6826/© 2017 Elsevier Ltd. All rights reserved. Journal of Atmospheric and Solar-Terrestrial Physics 164 (2017) 192–202