Fig 8 - uploaded by Kazuo Saito
Content may be subject to copyright.
Schematic chart of the numerical experiment. Figure 9 shows surface winds and MSLP with color shade of 3-hour accumulated precipitation and the height field and horizontal winds at 500 hPa and 300 hPa predicted by JMA-NHM for 0000 UTC 7 October 2009. The observed southerly ageostrophic winds over western part of Japan are well
Source publication
It is well-know that heavy rainfalls in Japan often occur when a typhoon or tropical depression exists on the sea far south of Japan. These phenomena, so-called 'pre-typhoon precipitation', are in many cases explained by the moisture transport over Japan from the tropical cyclone, however, the reason why the moisture is transported northward from t...
Context in source publication
Context 1
... wind. The JMA nonhydrostatic model (JMA-NHM; 2006;2007) was employed as the regional NWP model with a horizontal resolution of 10 km. Initial condition is given by the JMA operational mesoscale analysis at 1800 UTC, 6 October 2009, and boundary conditions are given by the 6 hourly JMA's operational global model forecasts from 1800 UTC, 6 October (Fig. ...
Similar publications
This study analyzes high-frequency wind data collected by research towers in the surface layer of Typhoons Hagupit (2008) and Chanthu (2010) to investigate the characteristics of the momentum flux, turbulent kinetic energy (TKE), drag coefficient, and dissipative heating (DH) during landfalls. It is found that the momentum flux TKE and DH increase...
Citations
The Indochina Peninsula (ICP) is dominated by a tropical monsoon climate, and changes of the prevailing winds here have a marked impact on moisture and aerosol transport. September to early October is within the monsoon retreat period that is preceded by a change in the zonal wind from westerly to easterly. Here, we show the long‐term change of the monsoon retreat date and its related climate factors. Climatologically, the zonal wind is primarily controlled by the meridional land–sea temperature gradient through the geostrophic balance. A simple physical model suggests that a 1 K increase in this gradient is associated with a zonal wind speed change of 2.17 m·s⁻¹, and this estimate is consistent with reanalyses. Over the most recent 40 years there has been a positive trend of 0.107 K·decade⁻¹ in the gradient, and linear regression shows that the average rate of delay of the summer monsoon retreat date over the ICP associated with trend in land–sea contrast is 23.5 day·K⁻¹. The mixing ratio gradient also makes a contribution to the monsoon retreat but its significance is lower than the land–sea temperature contrast. The ICP is located in a transitional zone bounded by three sub‐regions of Asia‐Pacific monsoon system; the delayed ICP monsoon retreat is most consistent with changes of the East Asian‐Western North Pacific monsoon.
Heavy rainfalls often occur when a tropical cyclone (TC) exists on the sea off the south coast. These pre-typhoon rainfalls (PRE) is associated with the northward moisture transport ahead of the TC. In this paper, we examine the northward moisture transport by the ageostrophic winds associated with typhoon T0918 (Melor) and its impact on PRE. According to a numerical simulation conducted in the previous study (Saito 2019), we analyzed the northward moisture fluxes by reproduced geostrophic and ageostrophic winds. Although the southerly ageostrophic winds are dominant mainly in the upper levels, the ageostrophic winds contribute to enhance the poleward water vapor transport for the upper and middle levels above 3 km.
To see the impact of the ageostrophic moisture transport on PRE, we conducted a sensitivity experiment where the model moisture in middle and upper levels over the sea off the south coast of western Japan was reduced. Precipitation over western Japan was decreased about 30% when the contributions in moisture fluxes by ageostrophic winds were removed. This result suggests that the northward ageostrophic winds associated with a TC enhance PRE by moistening the middle and upper atmosphere.
