Characteristics and Causal Analysis of an Extreme Gale on West Coast of Bohai Sea
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Abstract:
The observed process constitutes a combination of systemic cold air gale and thunderstorm gale. The convective system is induced and moves along with the front, resulting in sudden and extreme gale conditions akin to thunderstorm gales. Upon transitioning, the convective system mirrors the persistent traits of a systemic cold air gale. This study uses NCEP-FNL data, FY-4 satellite infrared cloud data, radar data, wind profile data, and automatic weather station data to investigate the characteristics and causes of the extreme gales. The principal findings are as follows: (1) The eastward progression of high trough at 500 hPa and low vortex at 850 hPa established a widened warm region at 850 hPa, as well as an unstable stratified complex along the west coast of the Bohai Sea. The transition of the front triggered convection, leading to extreme windy weather along the west coast. The reflectivity factor revealed that two bands of weak echoes along the west coast of the Bohai Sea were converging and intensifying into a single band, which then developed from a band to a bow echo with a gap in the front, as the system moved eastward. Notably, substantial velocity blurring and mid-level radial convergence emerged from the velocity diagram. (2) The gale event occurred in early spring when shortterm forecasts did not accommodate convective weather, accounting only for the manifestation of frontal precipitation and cold air gales. Prior to the emergence of convection, cold advection at 500 hPa and pronounced warm advection at 700-925 hPa were present over the west coast of the Bohai Sea. The unstable stratum between the upper-level cold and lower-level warm layers furnished favourable environmental conditions for the frontal transition to induce convection. In this context, the CAPE and DCAPE values derived from the NCEP forecast model served as a reference for thunderstorm and gale forecasting. (3) The gale progression was influenced by the downward momentum transfer of large-scale cold air, variable pressure winds, gradient winds induced by large-scale cold air, and the effects of mesoscale thunderstorm cold pool outflow invoked by convective systems. The systemic cold air gales, propagated due to the downward momentum transfer of largescale cold air, variable pressure winds and gradient winds, exerted an augmenting impact on the mesoscale thunderstorm outflow.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.