Tetsuya Takemi

This study investigates the relationship between the vertical development of tropical cumulus convection and the vertical profiles of environmental temperature and moisture in order to identify the factors responsible for determining the tropical cumulus heights. The analyses of observational data obtained in the tropical western Pacific region reveal a strong correlation between the development of shallow and middle‐topped cumulus clouds and the existence of dry layers in the middle to upper tr

It has been argued that frequent dust storm developments in east Asia in spring are closely related to midlatitude synoptic‐scale cyclone activity. This study investigates the relationship of springtime dust storms and other dust‐related phenomena in east Asia to the tracks and locations of synoptic‐scale cyclones by conducting statistical analyses of surface weather data, cyclone track data, and satellite data. Through these analyses, we discuss the role of cyclone activity on dust weather phen

Using the newly developed Weather Research and Forecasting (WRF) model, this study investigates the effects of subgrid mixing and numerical filtering in mesoscale cloud simulations by examining the sensitivities to the parameters in turbulence-closure schemes as well as the parameters in the numerical filters. Three-dimensional simulations of squall lines in both no-shear and strong-shear environments have been performed. Using the Smagorinsky or 1.5-order turbulent kinetic energy (TKE) subgrid

This study investigated the environmental factors responsible for the development of heavy rainfall in eastern Japan during the passage of Typhoon Hagibis (2019) by using mesoscale gridded analysis data as well as observed data. Environmental indices for diagnosing stability and moisture conditions were examined. It was found that the whole troposphere is almost saturated and the column total water vapor content is extremely large. In the lower troposphere we identified layers of moist absolutel

The structure and evolution of a long-lived squall line associated with a disastrous dust storm, called a black storm, that occurred over the arid region in northwest China are described. Data used in the present study were those from routine observations in China and those acquired from surface observations of the Heife River Field Experiment. The squall line evolved within an extremely dry environment in which surface water vapor mixing ratios were less than 2.5 g kg−1 and the level of free co

An extreme, damaging rainfall occurred in northern Kyushu in July 2017. Whether such an extreme rainfall is quantitatively captured by numerical models is a challenging issue. We investigate the influences of terrain representation in simulating a stationary convective system and the resulting heavy rainfall for this case by conducting a series of 167-m-resolution numerical experiments. By employing a high-resolution elevation dataset as well as a double-moment cloud microphysics scheme, the con

An intense tropical cyclone, Typhoon Jebi (2018), landed the central part of Japan and caused severe damages. Quantitative assessment of strong winds in urban districts under typhoon conditions is important to understand the underlying risks. As a preliminary study, we investigate the influences of densely built urban environments on the occurrence of wind gusts in an urban district of Osaka City during Typhoon Jebi by merging mesoscale meteorological and building-resolving large-eddy simulation

The environment for the development and evolution of linearly organized convective systems, i.e., squall lines is diverse for their existence in various climate regions. Understanding the behavior of squall lines under various environmental conditions is required for diagnosing and forecasting the development and intensity of the convective systems. The present study investigates the effects of environmental static stability on the squall‐line intensity by conducting a systematic series of ideal

The mechanisms responsible for the development and maintenance of long-lived squall lines in dry environments are investigated through two-dimensional numerical experiments by using a nonhydrostatic cloud model. The squall line environments are characterized by a low convective available potential energy (CAPE), low moisture content, and a high level of free convection (LFC), which are based on observations of a squall line over an arid region in China. Although these environments seem to be unf

This study numerically investigates the influences of global warming on Typhoon Vera (1959) by conducting pseudo-global warming experiments. It was found that the intensity of Typhoon Vera will be stronger in warmed climate conditions than in the actual September 1959 condition not only at the time of the typhoon’s maturity but also at the time of the landfall. Sensitivity experiments indicate that this projected increase in the typhoon intensity is robust, by taking into consideration the effec

Understanding the characteristics of urban airflows with complex geometrical features is very important from viewpoints of assessing strong wind hazards in the region. This study investigated turbulent airflows and strong wind hazards in an urban area by conducting large-eddy simulations (LESs) with explicit representations of buildings and structures. A business district, including historical architectures, of Kyoto City was chosen. The sensitivity experiments with realistic and idealized build