Constant Altitude Plan Position Indicator Research Articles

Distribution of ice particles in wintertime thunderclouds detected by a C band dual polarization radar: A case study

Distributions of radar echo intensities (ZH) and differential reflectivity factors (ZDR) for ice particles in Japan's wintertime thunderclouds are investigated using C band dual polarization radar observations conducted on January 12, 1990, as a case study. At the moment of lightning strokes, the percentage of low‐ZDR data points is increased around the cloud center, while that of high‐ZDR data points is increased near the cloud edge. These radar echoes indicate the backscattering properties from graupel particles and ice crystals, both of which play a critical role in thunderstorm electrification. The ice crystal echoes are primarily enhanced 5–15 min before the lightning stroke. At the moment of lightning stroke; however, they are slightly decreased, and the graupel echoes gradually increase the intensity. These characteristics are well described by the convective motion of the dominant ice particles in this observational case. In addition, graupel echoes of more than 40 dBZ are found for these thunderclouds on January 12, whereas the clouds which produced no lightning, but indicated the evidence of comparable electrification, did not show more than 40 dBZ on January 18, 1990. The lightning locations are seen along the edge of the cloud center with ZH ∼ 30 dBZ, where graupel and ice crystal echoes distribute at short range. Their distributions are then estimated by counting both low‐ and high‐ZDR data points on the constant altitude plan position indicator display, combined with their large and small echo intensities, respectively. Using polarimetric information (ZDR, ZH), the product numbers of graupel and ice crystal echoes in each 5 × 5 km area are found to be fairly well correlated with the lightning location. These results are thus obtained for the one case of the present thunderstorm event, but they may give some insights on evolution of thunderclouds and lightning discharges.

北陸地方における雷雲のレーダエコーとその発雷との関係の研究

In the present work, winter thunderclouds and active convective clouds were observed by means of radar with CAPPI (Constant Altitude Plan Position Indicator). The lightning activity is monitored by a local network of sferics direction finders around Komatsu Airport.In midwinter, from January to early March, active convective clouds, 30 dBZ echo tops of which develop up to the -20°C temperature level, exhibit very weak lightning activity called “Single-Flash Storm”, or sometimes fail to generate even a single lightning discharge. The altitude of the -10°C temperature level is between 1.8 to 1.4km in the former case. On the other hand, it is lower than 1.4km in the latter case. These significantly low altitudes of the -10°C temperature level are the main reason for keeping such clouds in a weak or non-lightning situation.Concerning the classification of the lightning activity, the author has proposed the following criteria:(a) When the altitude of the -10°C temperature level is higher than 1.8km, clouds exhibit strong lightning activity.(b) When the altitude of the -10°C temperature level is between 1.8 to 1.4km, clouds exhibit very weak or no lightning activity.(c) When the altitude of the -10°C temperature level is lower than 1.4km, clouds never generate a lightning discharge.Along with the results of thundercloud investigation stated in Part I of the present article (Michimoto, 1991), it is concluded that the necessary conditions for convective clouds to generate lightning discharge are as follows:(1) The 30 dBZ echo of the clouds has to develop at a level higher than the -20°C temperature level.(2) The altitude of the -10°C temperature level has to be higher than 1.4km.(3) The clouds have to involve rapid development of graupel particle precipitation; specifically, they have to involve formation and rapidly vertical movement of 40-to-50 dBZ echo cells.

Observations in Hailstorms Using the T-28 Aircraft System

Abstract This study relates data gathered during the penetration of hailstorms between 4.9 and 6.7 km MSL by an armored T-28 aircraft to detailed radar data of the hailstorms penetrated. These data recorded by the T-28 data system are combined with observations made by the author while piloting the T-28 through hailstorms. The radar data from the National Hail Research Experiment CPR-2 are specially prepared as Constant Altitude Plan Position Indicator (CAPPI) displays and vertical sections along the aircraft track for comparison with the data gathered by the aircraft system and pilot's observations. The results indicate that significant updrafts are frequently found well ahead of the high radar reflectivity zones. The updrafts are found to be relatively smooth while the high radar reflectivity zones are found to be very turbulent. Significant quantities of supercooled liquid water are found in the updraft regions. Significant airframe icing is found in the strong updrafts with the most severe icing along...