Abstract
This study investigated the relationship between variations in the atmospheric boundary layer height (ABLH) and typhoons over the Northwest Pacific using global navigation satellite system (GNSS) radio occultation (RO) data during the local summer typhoon season (July–October in the Northern Hemisphere) from 2007 to 2020. The minimum gradient of refractivity derived from COSMIC and COSMIC-2 was used to determine the ABLH. The RO profiles were co-located with the position of a typhoon track base within a 600 km space window and different time windows. ABLH climatology with a 2.5° × 2.5° horizontal resolution was developed, which can be used to obtain the interpolated mean ABLH at any target position. The mean ABLH at the central typhoon position in a specific year was compared with the results interpolated from the climatology of the same location (excluding the year in which the investigated typhoon occurred). In this paper, the results indicate that the ABLH is lower in the vicinity of typhoons relative to the undisturbed atmosphere by a significant amount, and that the reduction in ABLH ranges from 0.13 km to 0.39 km. It was also found that the ABLH was negatively correlated with wind speed, and that the mean correlation coefficient was −0.607. Moreover, similar results can be obtained via the RO water vapor partial pressure profile compared to the refractivity results.
Highlights
The atmospheric boundary layer (ABL) is the layer closest to the Earth’s surface, where turbulent processes often dominate the vertical redistribution of sensible heat, momentum, moisture, and aerosols [1]
The reason for this decrease was that a higher signal-to-noise ratio (SNR) improved the ability of COSMIC-2 to detect refractivity and other parameters at lower altitudes; many radio occultation (RO) profiles with atmospheric boundary layer height (ABLH) below 0.5 km were added into the calculation of ABLH climatology
The refractivity profiles derived from COSMIC (2007–2018) and COSMIC2 (2020) datasets during typhoon season over the Northwest Pacific were used to investigate the influence of a typhoon on the ABLH
Summary
The atmospheric boundary layer (ABL) is the layer closest to the Earth’s surface, where turbulent processes often dominate the vertical redistribution of sensible heat, momentum, moisture, and aerosols [1]. The ABLH is usually taken as the height at which the magnitude of the turbulence parameter becomes much smaller (~95%) than that at the surface layer when the vertical profiles of turbulent intensity and/or flux are measured, and it can be defined via the height of the temperature inversion layer when there are no turbulence data available due to unstable conditions [9]. The measurement of the vertical gradient of virtual potential temperature with a threshold and the parcel method can be used to identify the ABLH when flux data are not available [10,11,12]
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