Heavy Rainfall Amounts Research Articles

Synoptic-Scale Features Associated with Warm Season Heavy Rainfall over the Interior Southeastern United States

Previous research has established links between heavy rainfall and a wide variety of synoptic features and parameters. In this study, 312 heavy rainfall events are identified over the southeastern United States and used to construct a synoptic climatology that relates 14 synoptic features and parameters to the occurrence and amounts of heavy rainfall. To carry this out, an automated synoptic typing scheme is employed to classify the heavy rainfall sample according to several characteristics of the synoptic regime. This classification provides five distinct synoptic patterns that can be associated with heavy rainfall over the southeastern United States. Commonly occurring synoptic features in each synoptic pattern are highlighted and discussed. Correlation analysis is then used to relate the occurrence and strength of these features to the heavy precipitation totals. Heavy rainfall in four out of the five identified synoptic patterns is most frequently associated with high levels of moisture at the 700-mb level. Ridging in the 850-mb warm air advection field is common over the heavy rain area as well. Numerous relationships are identified between the heavy rainfall amounts and the character of synoptic features; however, the nature of these relationships is found to vary strongly according to the synoptic pattern.

1988年7月に長崎県で観測した梅雨末期の豪雨のメソスケールと対流スケールの特徴

A comprehensive observation during the late period of the Baiu season was performed in July, 1988, in the project "A Study of Mechanism and Prediction on Heavy Rainfalls during Rainy Season in Japan" (Asai, 1990). Spatially and temporally dense (-100 km, 3-6 h) sounding data and Doppler radar data were collected during this special observation. In this study, in order to investigate the mesoscale and convective scale features of the heavy rainfall events in the late period of the Baiu season, the low-level wind field and evolution processes of radar echoes were analyzed by using the Hokkaido University Doppler radar, which was located in Saikai town, Nagasaki Prefecture. Two successive mesoscale rainfall events associated with the Baiu front (Case 1 and Case 2) which were observed on July 17 and 18, 1988, formed the main units of analysis. Both rainfall events occurred in association with a cloud cluster. Heavy rainfall amounts exceeding 100 mm were experienced in limited areas during Cases 1 and 2 (for example, rainfall amounts at Isahaya during Case 1 and Case 2 were 165 mm/3h and 104 mm/3h, respectively). The Doppler radar analyses revealed important mechanisms of the heavy rainfall events, which are described briefly as follows. In Case 1, enhancement of the Baiu frontal convergence by gust fronts from convective clouds, and the merging between the Baiu frontal rainband and isolated echoes generated south of the Baiu front played an important role in the organization of a well developed rainband. The rainfall event of Case 2 occurred about 4 hours after Case 1 and in almost the same region. In Case 2, an organized arc-shaped echo caused the heavy rainfall, and gust fronts contributed to the organization of this echo. The advection of warm and moist air from the undisturbed region of the Case 1 rainfall also played an important role in its development. From these case studies, it can be concluded that mesoscale and convective scale features influencing the formation and maintenance of Baiu frontal rainbands are (1) enhancement of low level convergence by convective outflow (gust front), (2) merging effect of convective clouds, and (3) mesoscale contrast of temperature and rainfall produced by mesoscale rainfall.

A Comparative Analysis of the Temporal Variability of Lightning Observations and GOES Imagery

Lightning Positioning and Tracking System (LPATS) data received by the Cooperative Institute for Research in the Atmosphere via a real-time weather data network were used to study the temporal variability of lightning for a frontal system and hurricane that affected the United States in 1989. Our comparison of these data with GOES-7 imagery revealed that lightning data can help define the development, linearity, and maximum intensity of a frontal band as seen with the correlation of currents discharged by lightning to ground with associated IR temperature fields. Lightning data also revealed a dramatic increase in convection equatorward of Hurricane Chantal's vortex upon her rapid intensification and landfall, and the heavy rainfall amounts associated with the tropical storm correlated to areas of rather frequent lightning activity west of Galveston, Texas, on 1 August 1989.

Mesoscale Analysis of Pressure and Precipitation Patterns during AVE-SESAME 1979, 10–11 April

A mesoscale analysis of hourly surface data of pressure and precipitation is presented for the case of 10–11 April, during AVE-SESAME 1979. Barograph traces also are used in the analysis. Three distinct pressure waves traveling northeastward across Oklahoma and Missouri are found to be well correlated with thunderstorm activity and heavy rainfall amounts. Wave speeds appeared to propagate at approximately 25 m · s−1 and to have amplitudes ranging from 2 to 6 mb. The average time elapsed between successive wave passages at a particular station was 4 h. A ridge of high pressure passed a station about one hour after heavy precipitation had occurred.

The Precipitation under the Assumption of Dry Adiabatic Change and Moist Adiabatic Change of the Air

It is the purpose of this paper to make clear the condensation equation. Using this equation and the vertical motion computed from vorticity equation, an amount of heavy rainfall was calculated. In connection with this problem, the author attempts to calculate the amount of condensation of the vapour and vertical velocity under the assumption of not only dry adiabatic change but also moist adiabatic change of the air.