Fig. 3: Background wind profiles of the TC-SGWs.

a–c Composite area-mean background wind (m s⁻¹) within r = 1000 km around the TC center for SPSI, WP, and NAEP, respectively. The x-axis denotes the magnitude of the background wind, and the y-axis denotes the pressure level. The red and blue solid lines denote the zonal and meridional background wind, respectively. Considering that there are both easterly and westerly winds around the TC-SGWs as Fig. 1b−e, to show the magnitude of the easterly and westerly winds, respectively, and avoid offsetting each other, we composite area-mean easterly or westerly background wind profiles separately according to the direction of area-mean background wind at 3-hPa. The red dashed and dot-dashed lines denote the composited background wind profiles when the 3-hPa area-mean background winds are easterly and westerly, respectively. The light blue vertical and horizontal lines denote the zonal wind speed of −20 m s⁻¹ and height of 3 hPa, respectively. The composite dataset is from ERA5; see the “Methods” section for further details.