Hanako Y. Inoue

Finescale Doppler Radar Observation of a Tornado and Low-Level Misocyclones within a Winter Storm in the Japan Sea Coastal Region

Abstract Life histories of low-level misocyclones, one of which corresponded to a tornado vortex within a winter storm in the Japan Sea coastal region on 1 December 2007, were observed from close range by X-band Doppler radar of the East Japan Railway Company. Continuous plan position indicator (PPI) observations at 30-s intervals at the low-elevation angle revealed at least four cyclonic misocyclones within the head of the comma-shaped echo of the vortical disturbance under winter monsoon conditions. The meso-β-scale vortical disturbance developed within the weak frontal zone at the leading edge of cold-air outbreaks. High-resolution observation of misocyclones revealed the detailed structures of these misocyclones and their temporal evolution. As the parent storm evolved, a low-level convergence line was observed at the edge of the easternmost misocyclone. This convergence line was considered to be important for the initiation and development of the misocyclones and the tornado through vortex stretching...

Three-Dimensional VHF Lightning Mapping System for Winter Thunderstorms

AbstractA three-dimensional (3D) winter lightning mapping system employing very high frequency (VHF) broadband signals was developed for continuous remote observation in winter. VHF broadband pulses radiated by leader progression are received with three discone antennas arranged in a triangle (20–30 m) and recorded on a high-speed digital oscilloscope (1.25-GHz sampling) with GPS digital timing data. The two-dimensional (2D) mapping for azimuth and elevation of the VHF radiation sources was conducted by computing the arrival time differences of three pulses using a cross-correlation technique. From azimuth and elevation data from two sites extracted within a given time frame, 3D lightning mapping was performed using the triangulation scheme. An observation network for winter lightning was constructed within a comprehensive meteorological observation network in the Shonai area, which is located on the coast of the Japan Sea. This report includes the preliminary 2D and 3D mapping of winter lightning observe...

Analysis of the horizontal two-dimensional near-surface structure of a winter tornadic vortex using high-resolution in situ wind and pressure measurements

The horizontal two-dimensional near-surface structure of a tornadic vortex within a winter storm was analyzed. The tornadic vortex was observed on 10 December 2012 by the high-resolution in situ observational linear array of wind and pressure sensors (LAWPS) system in conjunction with a high-resolution Doppler radar. The 0.1 s maximum wind speed and pressure deficit near the ground were recorded as 35.3 m s−1 and −3.8 hPa, respectively. The horizontal two-dimensional distributions of the tornadic vortex wind and pressure were retrieved by the LAWPS data, which provided unprecedented observational detail on the following important features of the near-surface structure of the tornadic vortex. Asymmetric convergent inflow toward the vortex center existed. Total wind speed was strong to the right and rear side of the translational direction of the vortex and weak in the forward part of the vortex possibly because of the strong convergent inflow in that region. The tangential wind speed profile of the vortex was better approximated using a modified Rankine vortex rather than the Rankine vortex both at 5 m above ground level (agl) and 100 m agl, and other vortex models (Burgers-Rott vortex and Wood-White vortex) were also compared. The cyclostrophic wind balance was violated in the core radius R0 and outside the core radius in the forward sector; however, it was held with a relatively high accuracy of approximately 14% outside the core of the vortex in the rearward sector (from 2 R0 to 5 R0) near the ground.

Three-dimensional lightning characteristics relative to reflectivity and airflow structure in winter thunderstorm

A winter thunderstorm was observed in the Shonai area in the northern part of Japan on 30 November 2010. Data from three-dimensional lightning mapping system and two X-band Doppler radars were used to analyze the spatial-temporal relationship between winter lightning channel, reflectivity core, and airflow structure in the thunderclouds. A lightning leader propagating from a rim of echo region to the echo region with high reflectivity involving large vertical vorticity was visualized in 3D. This result indicates that strong updraft caused by airflow convergence in the precipitation system contributed to accumulate positive charges around -10°C level and enhance vertical vorticity by stretching on the convergence line.

Multi‐wavelength radar algorithm with Doppler function for the retrieval of cloud microphysics with precipitation

We developed the retrieval algorithm for clouds accompanying precipitation. In order to obtain the vertical structure of cloud microphysics, W‐, Ka‐ and X‐ band radars with Doppler capability were used. We first considered six different particle types and the scattering properties of the non‐spherical ice particles were calculated at these frequencies by using the discrete dipole approximation (DDA). Then dual wavelength ratios (DWR) and the reflectivity‐weighted terminal velocities (Vtz) for the six particle types were estimated. It was found that the DWR for W‐ and Ka‐ band radars depended on particle shape, orientation and size when particle effective radius exceeds about 60 μ m . DWR for Ka‐ and X‐ band radars also showed the similar dependences but for larger size than the DWR for X and Ka band radars. The Vtz also show the strong dependence on shape, orientation and size for large size. The retrieval algorithm consists of two parts; (1) large particle mode from the combination of DWRs and VTzs from W‐, Ka‐ and X‐ band radars measurements and (2) small particle mode from the radar reflectivity and Vtz from Ka‐ band. We examined the cloud microphysics from the radar data observed in Niigata in December 2007, in the field experiment of Japanese Cloud Seeding Experiment for Precipitation Augmentation (JACSEPA). Retrievals of microphysics were performed for two cases. The retrieval results were compared with the in‐situ data and found some agreement.