Short‐wave directional properties in the vicinity of atmospheric and oceanic fronts

Abstract

The author estimated and investigated mean wave directions and directional spread parameters of 0.505 Hz ocean waves using data from 24.5 MHz‐HF ocean radar. The author described temporal and spatial variabilities of the short‐wave field. The short‐wave direction is a good indication of wind direction. The spread parameter was related to the variability of wind direction. The author examined the case that an atmospheric front or an oceanic front exists in the HF ocean radar observation area. In the case of an atmospheric front the short‐wave direction changed with the passage of the atmospheric front. Furthermore, the complicated frontal structure, which cannot be verified from a weather chart, was revealed. Narrow directional spread was observed in the vicinity of the convergent front, which was reproduced using a simplified model based on the wave action conservation law. The result shows that wave refraction associated with a frontal convergent zone is important in determining the spatial variability of short‐wave directional properties.

Ocean wave directional spectra estimation from an HF ocean radar with a single antenna array: Observation

“…The correlation coefficient was R c = 0.88 (Table 1), and it was found to be possible to estimate wind directions by HF ocean radar. However, the accuracy of estimations of wind direction was poorer than those of Hisaki [2002]. The RMS difference from the linear regression line is 31° in the work of Hisaki [2002], but 44° in the present case.…”

“…However, the accuracy of estimations of wind direction was poorer than those of Hisaki [2002]. The RMS difference from the linear regression line is 31° in the work of Hisaki [2002], but 44° in the present case. Note that dual radars were used by Hisaki [2002], while a single radar was used in the present study.…”

“…These parameters are randomly generated for pre‐decided parameter ranges, seeking parameters which will minimize the sum of the weighted squared differences of constraints (C1) and (C2). Wind direction is also estimated in the first step, with the initial wind direction estimated from the ratio of first‐order scattering as in the method described by Hisaki [2002].…”

“…It is important to be able to estimate ocean surface wave spectra for a wide variety of marine applications including uses in physical oceanography, wave forecasting, ship routines and coastal engineering. One promising technology for wave measurement is high‐frequency (HF) ocean radar, which radiates HF radio waves to the sea surface and measures ocean surface currents [ Barrick et al , 1977; Prandle and Ryder , 1985; Takeoka et al , 1995; Hisaki et al , 2001; Hisaki and Naruke , 2003] and surface waves [ Hisaki , 1996, 2002, 2004, 2005] by analyzing the Doppler spectra of backscattered signals.…”

Southward recirculation of the East China Sea Kuroshio west of Okinawa Island

“…We analyzed ocean surface currents observed by HF ocean radars. HF ocean radar is used to measure ocean surface currents [e.g., Barrick et al, 1977;Prandle and Ryder, 1985;Takeoka et al, 1995;Hisaki et al, 2001;Hisaki and Naruke, 2003] and surface waves [e.g., Hisaki, 1996Hisaki, , 2002Hisaki, , 2004Hisaki, , 2005Hisaki, , 2006 over broad spatial areas. The method is to radiate high-frequency radio waves and analyze the backscattered signals from the ocean.…”