Rainfall distribution of five landfalling tropical cyclones in the northwestern Australian region

Quart J Royal Meteoro Soc

2014

The precipitation pattern of a landfalling tropical cyclone (TC) with and without a weak environmental vertical wind shear (VWS) is investigated using WRF/NCAR model simulations under idealized conditions. In the simulations without VWS, results show that for the outer band (r ∼ 100–300 km), the cold and dry air originating over smooth land is advected offshore, reduces the stability and develops a band of rainfall on the eastern side of the TC, while the rough land surface tends to trigger more rainfall to the west. For the inner core (r< 100 km), there is only small rainfall asymmetry when the land surface is smooth and dry, but with a rough land surface, the rainfall asymmetry becomes evident and generally stronger rainfall is found over the land areas to the west. Further experiments are performed to compare the effects from weak environmental VWS and land–sea contrast. It is found that the storm‐scale (within 400 km from TC centre) VWS changes continuously in direction and magnitude due to asymmetric diabatic heating and accompanying upper‐level winds. The rainfall pattern in the inner‐core region follows closely the storm‐scale VWS with a downshear‐left relationship regardless of the surface properties, while in the outer‐band region, rainfall distribution is first strongly affected by the surface roughness before landfall and by the environmental VWS afterwards. Therefore, an evolving rainfall–VWS (both environmental and due to storm‐scale dynamics) relationship during TC landfall results.

Section: Discussionmentioning

confidence: 99%

Section: Comparison Of Environmental Vws and Land–sea Contrastmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Modelling the effects of land–sea contrast on tropical cyclone precipitation under environmental vertical wind shear

Cheung

Quart J Royal Meteoro Soc

2014

“…Corbosiero and Molinari, ; Chen et al ., ; Cecil, ; Ueno, ) and land properties (e.g. Li et al ., , , ), such as moisture availability, surface friction and topography, may contribute to the different distributions of convection for TCs making landfall from different directions. The results of such an investigation are presented in the next section.…”

Section: Categorization Of Landfalling Tropical Cyclone Rainfall Asymmentioning

confidence: 99%

“…In addition, the impacts of land properties on landfalling TC rainfall asymmetries on the South China coast have received little attention and have not been systematically documented (e.g. Li et al ., ; Li et al ., , ). These form the foci of the present study.…”

Section: Introductionmentioning

confidence: 99%

Rainfall asymmetries of landfalling tropical cyclones along the South China coast

Meteorological Applications

Wong

2018

The rainfall distribution associated with landfalling tropical cyclones (TCs) along the South China coast are examined using radar data from Hong Kong Observatory (HKO). This preliminary study relates the landfall direction, and possible rotations/transitions of TC rainfall asymmetries before and after the landfall. Three types of landfalling TCs on the South China coast are categorized: from the east, normal to the coast and from the southwest. For those from the east, the rainfall maximum rotates anticyclonically from the southwest before later landfall to the northwest. TCs making landfall perpendicular to the coast have a rainfall maximum remaining in the southwest quadrant throughout the landfall process. For TCs making landfall from the southwest, the rainfall maximum rotates cyclonically from the southeast before later landfall to the northeast. The relative importance of the impact of land properties and vertical wind shear on these rainfall asymmetries is investigated by using a numerical model. Sensitivity tests show that the rotations/transitions of landfalling TC rainfall asymmetry appear to be insensitive to land properties (e.g. moisture availability, surface friction and topography), but result primarily from changes in the orientations of the vertical wind shear in the environment. However, the surface friction of the landmass appears to contribute to the enhancement of rainfall intensity.

Numerical study on the development of asymmetric convection and vertical wind shear during tropical cyclone landfall

Cheung

2013

Q.J.R. Meteorol. Soc.

Idealized simulations on an f‐plane of tropical cyclone (TC) landfall under a quiescent environment in the Southern Hemisphere are performed to investigate the effects of land–sea surface contrast on precipitation. In the control simulation, with realistic roughness and moisture over land to the south of the TC, the simulated vortex moves toward land due to a land‐induced steering flow. The abrupt decrease (increase) of tangential wind at the surface leads to convergence (divergence) on the onshore (offshore) flow side. Enhanced convergence at the top of the planetary boundary layer is found on both onshore and offshore sides and is caused by advection from the surface and the enhanced offshore radial wind. The boundary‐layer top convergence pattern is consistent with the rainfall distribution. Vertical wind shear develops during the landfall process associated with the low‐ and upper‐level asymmetric flows across the model domain. The wavenumber‐1‐like low‐level asymmetric flow is introduced by an asymmetric geopotential height field that is generated by the large area of frictionally induced convergence on the onshore side and divergence on the offshore side. The upper‐level asymmetric flow is attributed to asymmetric convection and associated diabatic heating after landfall. Most rainfall is found in the down‐shear right quadrant, which is consistent with previous studies that focused on the effect of environmental shear. Although the existence of feedback from the vertical wind shear to rainfall remains an open question, the relation between maximum rainfall and vertical wind shear is robust, especially when the shear magnitude is large after landfall.