Tropical cyclone induced asymmetry of sea level surge and fall and its presentation in a storm surge model with parametric wind fields Machuan Peng a, * , Lian Xie a , Leonard J. Pietrafesa b a Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Box 8202, Raleigh, NC 27695-8208, United States b College of Physical & Mathematical Sciences, Box 8201, North Carolina State University, Raleigh, NC, United States Received 22 July 2005; received in revised form 14 March 2006; accepted 15 March 2006 Available online 11 May 2006 Abstract The asymmetry of tropical cyclone induced maximum coastal sea level rise (positive surge) and fall (negative surge) is studied using a three-dimensional storm surge model. It is found that the negative surge induced by offshore winds is more sensitive to wind speed and direction changes than the positive surge by onshore winds. As a result, negative surge is inherently more difficult to forecast than positive surge since there is uncertainty in tropical storm wind forecasts. The asymmetry of negative and positive surge under parametric wind forcing is more apparent in shallow water regions. For tropical cyclones with fixed central pressure, the surge asymmetry increases with decreasing storm translation speed. For those with the same translation speed, a weaker tropical cyclone is expected to gain a higher AI (asymmetry index) value though its induced maximum surge and fall are smaller. With fixed RMW (radius of maximum wind), the relation- ship between central pressure and AI is heterogeneous and depends on the value of RMW. Tropical cyclone’s wind inflow angle can also affect surge asymmetry. A set of idealized cases as well as two historic tropical cyclones are used to illustrate the surge asymmetry. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Asymmetry; Storm surge; Tropical cyclone; Parametric wind 1. Introduction Tropical cyclone (TC) induced storm surge is a major threat to coastal residents. Measures of the impacts of these storms on coastal communities are in the loss of human lives and property destruction. Fortunately, the 1463-5003/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ocemod.2006.03.004 * Corresponding author. Tel.: +1 919 515 1436; fax: +1 919 515 7802. E-mail address: mpeng@ncsu.edu (M. Peng). Ocean Modelling 14 (2006) 81–101 www.elsevier.com/locate/ocemod