Taro Shinoda

Influential Role of Moisture Supply from the Kuroshio/Kuroshio Extension in the Rapid Development of an Extratropical Cyclone

AbstractThis study focused on an explosive cyclone migrating along the southern periphery of the Kuroshio/Kuroshio Extension in the middle of January 2013 and examined how those warm currents played an active role in the rapid development of the cyclone using a high-resolution coupled atmosphere–ocean regional model. The evolutions of surface fronts of the simulated cyclone resemble the Shapiro–Keyser model. At the time of the maximum deepening rate, strong mesoscale diabatic heating areas appear over the bent-back front and the warm front east of the cyclone center. Diabatic heating over the bent-back front and the eastern warm front is mainly induced by the condensation of moisture imported by the cold conveyor belt (CCB) and the warm conveyor belt (WCB), respectively. The dry air parcels transported by the CCB can receive large amounts of moisture from the warm currents, whereas the very humid air parcels transported by the WCB can hardly be modified by those currents. The well-organized nature of the ...

Future increase of supertyphoon intensity associated with climate change

Increases of tropical cyclone intensity with global warming have been demonstrated by historical data studies and theory. This raises great concern regarding future changes in typhoon intensity. The present study addressed the problem to what extent supertyphoons will become intense in the global warming climate of the late 21st century. Very high resolution downscale experiments using a cloud-resolving model without convective parameterizations were performed for the 30 most intense typhoons obtained from the 20 km mesh global simulation of a warmer climate. Twelve supertyphoons occurred in the downscale experiments, and the most intense supertyphoon attained a central pressure of 857 hPa and a wind speed of 88 m s−1. The maximum intensity of the supertyphoon was little affected by uncertainties that arise from experimental settings. This study indicates that the most intense future supertyphoon could attain wind speeds of 85–90 m s−1 and minimum central pressures of 860 hPa.

Characteristics of Vertical Circulation in the Convective Boundary Layer over the Huaihe River Basin in China in the Early Summer of 2004

The purpose of this study is to clarify the characteristics of the convective boundary layer (CBL) over a humid terrestrial area, the Huaihe River basin in China, which is covered by a large, nearly flat plain with uniform farmland. Data were collected in early summer 2004 using a 32-m flux tower and a 1290-MHz wind profiler radar. When mature wheat fields or bare fields dominated (the first period), the sensible heat flux (SHF) from the land surface was nearly equal to the latent heat flux (LHF). After vegetation changed to paddy fields (the second period), the LHF was much larger than the SHF. Two clear days from the first and second periods were selected and are referred to as the dry case and wet case, respectively. For the dry case, a deep CBL developed rapidly from the early morning, and thermal updrafts in the CBL were vigorous. For the wet case, a shallow CBL developed slowly from late morning, and thermals were weak. To study the thermodynamic process in the CBL, a large-eddy simulation (LES) was conducted. The simulation adequately reproduced the surface heat flux and the CBL development for both the dry case and the wet case. For the dry case, sensible heat contributed to nearly all of the buoyancy flux. In contrast, for the wet case, heat and moisture made equal contributions. The large contribution of moisture to the buoyancy is one of the main characteristics of the CBL over humid terrestrial areas.

Response of rapidly developing extratropical cyclones to sea surface temperature variations over the western Kuroshio–Oyashio confluence region

The dynamical response of rapidly developing extratropical cyclones to sea surface temperature (SST) variations over the western Kuroshio–Oyashio confluence (WKOC) region was examined by using regional cloud-resolving simulations. This study specifically highlights an explosive cyclone that occurred in early February 2014 and includes a real SST experiment (CNTL run) and two sensitivity experiments with warm and cool SST anomalies over the WKOC region (warm and cool runs). The results derived from the CNTL run indicated that moisture supply from the ocean was enhanced when the dry air associated with the cold conveyor belt (CCB) overlapped with warm currents. Further, the evaporated moisture contributed substantially to latent heat release over the bent-back front with the aid of the CCB, leading to cyclone intensification and strengthening of the asymmetric structure around the cyclones center. Such successive processes were more active in the warm run than in the cool run. The dominance of the zonally asymmetric structure resulted in a difference in sea level pressure around the bent-back front between the two runs. The WKOC SST variations have the potential to affect strong wind distributions along the CCB through modification of the cyclones inner system. Additional experiments with two other cyclones showed that the cyclone response to the WKOC SST variations became evident when the CCB north of the cyclones center overlapped with that region, confirming that the dry nature of the CCB plays an important role in latent heat release by allowing for larger moisture supply from the ocean.

A Hydrometeor Classification Method for X-Band Polarimetric Radar: Construction and Validation Focusing on Solid Hydrometeors under Moist Environments

AbstractA fuzzy-logic-based hydrometeor classification (HC) method for X-band polarimetric radar (X-pol), which is suitable for observation of solid hydrometeors under moist environments producing little or no hail, is constructed and validated. This HC method identifies the most likely hydrometeor at each radar sampling volume from eight categories: 1) drizzle, 2) rain, 3) wet snow aggregates, 4) dry snow aggregates, 5) ice crystals, 6) dry graupel, 7) wet graupel, and 8) rain–hail mixture. Membership functions are defined on the basis of previous studies. The HC method uses radar reflectivity Zh, differential reflectivity Zdr, specific differential phase Kdp, and correlation coefficient ρhv as its main inputs, and temperature with some consideration of relative humidity as supplemental information. The method is validated against ground and in situ observations of solid hydrometeors (dry graupel, dry snow aggregates, and ice crystals) under a moist environment. Observational data from a ground-based ima...

A positive feedback process related to the rapid development of an extratropical cyclone over the Kuroshio/Kuroshio Extension

AbstractThe active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resu...

A positive feedback process between tropical cyclone intensity and the moisture conveyor belt assessed with Lagrangian diagnostics

Using a cloud-resolving regional model and Lagrangian diagnostics, we assess a positive feedback process between tropical cyclone (TC) intensity and the moisture conveyor belt (MCB), which connects a TC and the Indian Ocean (IO), the South China Sea (SCS), and the Philippine Sea (PS) vapors, from a macroscopic view. We performed sensitivity experiments that modified the observed sea surface temperature (SST) field over the IO and the SCS to regulate the MCB behavior, and we examined the remote response of a prototypical TC. The results show that the connection between MCB formation and TC development is very robust, which was also observed in another TCs case. The MCB plays a vital role in transporting lots of moist air parcels toward the TC from the IO, SCS, and PS regions. The transported parcels, which further gained the underlying ocean vapor along the MCB, are easily trapped in the inner core by radial inflow in the atmospheric boundary layer and, subsequently, release latent heat around the eyewall, resulting in the TCs intensifying. This acts to further penetrate the moist parcels of remote ocean origin into the inner core through the enhanced and expanded inflow. An additional experiment suggested that the MCB is not formed unless the westward propagation of equatorial waves induced by TC heating overlaps with the background monsoon westerlies. These findings support the reliability and validity of TC-MCB feedback.

Seasonal change of the atmospheric boundary layer over Huaihe River basin in China

The Huaihe River basin has dry winter and wet summer seasons, and the structure of the atmospheric boundary layer shows the seasonal march. The change was continuously observed using a flux tower, a Doppler sodar, and a boundary layer profiler for more than two years. The mixed layer development was strongly affected by the surface conditions, that is, the wheat field, bare soil, and paddy field. When the surface is wet, the development of the mixed layer is weak and vice versa. Generally, the development was controlled by the surface sensible heat flux. But the development of the mixed was also affected by large scale up/downdraft. When a large scale subsidence exists, the development of the mixed layer is suppressed. A so-called LES simulation was performed in order to study the vertical profiles of the sensible heat and latent heat fluxes. It was found that the profile over paddy field is in between those over dry land and over ocean. The importance of the buoyancy due to the water vapor was also confirmed.