Observed Ocean Surface Winds and Mixed Layer Currents Under Tropical Cyclones: Asymmetric Characteristics

Abstract

Tropical cyclones (TC) transfer kinetic energy to the upper ocean and thus accelerate the ocean mixed layer (OML) currents. However, the quantitative link between near‐surface currents and high wind speeds, under extreme weather conditions, remains poorly understood. In this study, we use multi‐mission satellites and drifting‐buoy observations to investigate the connections between TC surface winds and currents, including their spatial distribution characteristics. Observed ageostrophic current speeds in the OML increase linearly with wind speeds (for the range 20–50 m/s). The ratios of the ageostrophic current speeds to the wind speeds are found to vary with TC quadrants. In particular, the mean ratio is around 2% in the left‐front and left‐rear quadrants with relatively small variability, compared to between 2% and 4% in the right‐front and right‐rear quadrants, with much higher variations. Surface winds and currents both exhibit strong asymmetric features, with the largest wind speeds and currents on the TC right side. In the eyewall region of Hurricane Igor, high winds (e.g., about 47 m/s) induce strong currents (about 2 m/s). The directional rotations of surface winds and currents are resonant and dependent on the location within the storm. Wind directions are approximately aligned with current directions in the right‐front quadrant; a difference of about 90° occurs in the left‐front and left‐rear quadrants. The directional discrepancy between winds and currents in the right‐rear quadrant is smaller. Reliable observations of the wind‐current relation, including asymmetric features, support published theories developed in idealized numerical experiments to explain the upper ocean response to TCs.

Assessment and Calibration of ERA5 Severe Winds in the Atlantic Ocean Using Satellite Data

“…Marine winds have great importance in several ocean engineering sectors, including platform design and operations, oil spill modeling, ship routing, offshore wind energy, and alert of extreme events, among others. Besides these direct applications, surface winds on the ocean play a fundamental role in wave generation [1,2] and wave modeling [3][4][5][6], surface currents [7,8], and sea level changes [9,10]. Therefore, the accuracy of ocean winds gathers a wide range of direct and indirect elements supporting a variety of ocean modeling applications, including climate studies [11][12][13][14][15] and statistical analyses [16,17].…”

Mapping Radial Ocean Surface Currents in the Outer Core of Hurricane Maria From Synthetic Aperture Radar Doppler Measurements

“…Thus, they generate strong surface and sub-surface currents, and impact the atmosphere and marine boundary layer through air-sea interactions, with feedbacks of moisture, momentum, mass and including climate-related greenhouse gases such as CO2. Various instruments have been used to measure ocean currents during hurricanes, including Airborne eXpendable Current Profilers (AXCP) [1], Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats [2], underwater gliders and wave gliders [3]- [4], uncrewed surface vehicles (e.g., saildrone) [5]- [6], and surface drifters [7]- [8]. These devices provide high-quality measurements of near-surface currents, depth-average currents, and current profiles, even under extreme weather conditions.…”

“…Cross swell dominates in the majority of hurricane regions [16]- [17]. Moreover, the strongest current is observed to the right side of the storm track [8], [18]. Thus, surface current retrieval under hurricane conditions is a challenging task.…”

Tropical Cyclones Related Wind Power on Oceanic Near‐Inertial Oscillations

“…Velocity data sets from drifters have indeed been widely utilized to investigate the sea surface current response to TCs (Chang et al., 2013; Fan et al., 2022; Wang et al., 2022). These data sets can also be applied to estimate the global wind power on NIOs (Liu et al., 2019).…”