Comment on ‘‘Importance of pre-existing oceanic conditions to upper ocean response induced by Super Typhoon Hai-Tang’’ by Z.-W. Zheng, C.-R. Ho, and N.-J. Kuo Akiyoshi Wada, 1 Kanako Sato, 2 Norihisa Usui, 1 and Yoshimi Kawai 2 Received 3 December 2008; revised 4 March 2009; accepted 7 April 2009; published 13 May 2009. Citation: Wada, A., K. Sato, N. Usui, and Y. Kawai (2009), Comment on ‘‘Importance of pre-existing oceanic conditions to upper ocean response induced by Super Typhoon Hai-Tang’’ by Z.-W. Zheng, C.-R. Ho, and N.-J. Kuo, Geophys. Res. Lett., 36, L09603, doi:10.1029/2008GL036890. 1. Introduction [1] Understanding the impact of pre-existing oceanic conditions on the upper ocean response to tropical cyclones (TCs) is one of the important issues for understanding the short-term occurrence of TC-ocean interaction and its im- pact on TC intensity. Zheng et al. [2008] showed that pre- existing cyclonic flow represented by negative sea-surface height anomalies (SSHA) played a crucial role in enhancing sea-surface cooling (SSC) caused by Typhoon Hai-Tang in 2005. On the other hand, the impact of initial oceanic mixed- layer depth and the vertical sea-temperature gradient in the thermocline on the amplitude of SSC has been considered to be small compared with that of the Ekman pumping and entrainment/vertical turbulent mixing [e.g., Wada, 2002]. Therefore, we hardly accept the discussion of Zheng et al. [2008] that the impact of Ekman pumping on SSC is less significant for local SSC occurred in certain areas than that of pre-existing oceanic condition. [2] Zheng et al. [2008] provide no quantitative evidence that SSC caused by the passage of Hai-Tang is irrelevant to the Ekman pumping or that the amplitude of SSC caused by the Ekman pumping is negligibly smaller than that due to relatively low sea surface height (SSH). In this paper, we revisit the relationship between SSC and SSH using a daily oceanic reanalysis dataset [Wada and Usui, 2007] produced by the North Pacific version of the Japan Meteorological Agency/Meteorological Research Institute Multivariate Ocean Variational Estimation system (MOVE) [Usui et al., 2006] in section 2. In section 3, we revisit the impact of the pre-existing oceanic condition on the ocean response to Hai- Tang using the Argo profiling float data. Section 4 presents our concluding remarks. 2. SSH and Ekman Pumping [3] Figure 1a depicts the horizontal distribution of ten- day mean SSH and maximum SSC from 1 to 10 July in 2005. Maximum SSC is defined here as the maximum decrease in sea-surface temperature (SST) from the first day (1 July in 2005) to the corresponding day. Figure 1b presents a distribution similar to that in Figure 1a but for an analyzed period from 11 to 20 July in 2005; the maximum decrease in SST is calculated from 11 July in 2005 to the corresponding day. As Zheng et al. [2008] suggested, we can capture relatively low SSH in certain areas using the MOVE data (Figure 1a): around 23°N, 144°E (C1), 22.5°N, 135°E (C2), 20°N, 130°E (C3) and 21°N, 125°E (C4). In Figure 1a, we can find low SSH areas C1, C2, C3 and C4 at almost the same places as Zheng et al. [2008] and Figure 1b. The stationary low SSH areas suggest that low SSH has already been formed and that these areas exist as pre-existing oceanic conditions. In Figure 1b, we can capture salient SSC in certain areas around 25°N, 140°E and 25°N, 125°E. Due to the relatively rough (0.5°  0.5°) horizontal resolution of MOVE data and wind forcing used in MOVE [see Usui et al., 2006] for resolving in situ SSC caused by a TC, MOVE data underestimate the amplitude of SSC caused by the passage of Hai-Tang compared with high-resolution satellite data shown by Zheng et al. [2008]. Nevertheless, each local SSC event presented in Figure 1b is caused by the passage of Hai-Tang by comparison of SSC between Figures 1a and 1b. [4] Comparing the horizontal distribution of SSH in Figure 1a with that in Figure 1b, we see that the amount of SSH around C4 from 11 to 20 July (Figure 1b) is much lower than that from 1 to 10 July (Figure 1a). According to best-track data archived in the Japan Meteorological Agency, Hai-Tang passed through areas around C3 and C4 (Figure 1b). This suggests the possibility that the Ekman pumping occurs around C3 and C4 during the passage of Hai-Tang. On the other hand, the SSHs around C1 and C2 hardly change even though SSC appears saliently after the passage of Hai-Tang. Their locations are far from the center positions of Hai-Tang (Figure 1b). According to the best-track data, Hai-Tang’s radius of 15 m s 1 wind speed was from 130 to 240 nautical miles (from 240 to 450 kilometers) at most when Hai-Tang passed near C1 and C2. Therefore, we should clearly distin- guish the formation process of local SSC around C1 and C2 from that around C3 and C4. [5] Hai-Tang’s moving speed was nearly 8 m s 1 around C3 at 0000 UTC on 16 July, which was relatively faster than nearly 5 m s 1 around C4 at 0000 UTC on 17 July [Zheng et al., 2008]. These moving speeds exceed the phase speed of the first baroclinic mode (3ms 1 ), indicating that near- inertial currents are generated behind Hai-Tang on the right side of the track. The near-inertial currents are responsible for the right-side bias of SSC alongside the track due to shear-induced entrainment at the mixed-layer base. The GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L09603, doi:10.1029/2008GL036890, 2009 1 Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan. 2 Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan. Copyright 2009 by the American Geophysical Union. 0094-8276/09/2008GL036890 L09603 1 of 4