Abstract
Tropical cyclone (TC) surface wind asymmetry is investigated by using wind data acquired from an L-band passive microwave radiometer onboard the NASA Soil Moisture Active Passive (SMAP) satellite between 2015 and 2017 over the Northwest Pacific (NWP) Ocean. The azimuthal asymmetry degree is defined as the factor by which the maximum surface wind speed is greater than the mean wind speed at the radius of the maximum wind (RMW). We examined storm motion and environmental wind shear effects on the degree of TC surface wind asymmetry under different intensity conditions. Results show that the surface wind asymmetry degree significantly decreases with increasing TC intensity, but increases with increasing TC translation speed, for tropical storm and super typhoon strength TCs; whereas no such relationship is found for typhoon and severe typhoon strength TCs. However, the degree of surface wind asymmetry increases with increasing wind shear magnitude for all TC intensity categories. The relative strength between the storm translation speed and the wind shear magnitude has the potential to affect the location of the maximum wind speed. Moreover, the maximum degree of wind asymmetry is found when the direction of the TC motion is nearly equal to the direction of the wind shear.
Highlights
Tropical cyclones (TCs) can induce storm surges and intense rainfall during landfall, thereby causing serious damage to society and affecting the safety of residents in coastal areas
Previous studies have shown that both storm motion and environmental vertical wind shear are the primary factors that account for TC surface wind asymmetries [15,16,19,21,22]
We used spaceborne radiometer wind data to investigate the effect of storm motion and wind shear on TC wind asymmetry, and we suggest that the relative strength between the storm translation speed and the wind shear magnitude can affect the location of the maximum wind speed
Summary
Tropical cyclones (TCs) can induce storm surges and intense rainfall during landfall, thereby causing serious damage to society and affecting the safety of residents in coastal areas. Meteorologists usually determine TC intensity by identifying the MWS; understanding the two-dimensional surface wind structure has great importance. Efforts have been made to understand the possible reasons for TC surface wind asymmetry by considering large-scale environmental impacts, such as the beta effect, vertical shear of environmental flow, and uniform environmental flows, on storm intensity. It is suggested that these environmental effects induce quasi-stationary asymmetries near the TC eyewall and exert inhibitory actions on storm intensity [1]. Previous studies have shown that other factors may affect TC structural asymmetries, including variations in surface friction [2], Rossby waves [3], and blocking actions [4]
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