Showing papers on "Air-mass thunderstorm published in 2016"

The origin of infrasonic ionosphere oscillations over tropospheric thunderstorms

Abstract: Thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere, but it is not clear what processes or which parts of the thunderstorm generate the oscillations. In this paper, we present a new technique that uses an array of ground-based GPS total electron content (TEC) measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms. The location technique utilizes instantaneous phase differences between pairs of GPS-TEC measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and other related parameters. In this preliminary study, the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations. The located sources are compared in time and space with thunderstorm development and lightning activity. Sources are often found near the main storm cells, but they are more likely related to the downdraft process than to the updraft process. As a result, the sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high-altitude sprites discharges.

Lightning Location System Data from Wind Power Plants Compared to Meteorological Conditions of Warm- and Cold Thunderstorm Events

Abstract: Conditions of Warmand Cold Thunderstorm Events DTU Orbit (17/12/2018) Lightning Location System Data from Wind Power Plants Compared to Meteorological Conditions of Warmand Cold Thunderstorm Events Five years of Lightning Location System (LLS) data from five different wind turbine sites in Europe are analysed. The sites are located in Croatia, Italy, Spain, France and one offshore wind power plant in the North sea. Each location exhibits individual characteristic properties in terms of topography, height above mean sea level (AMSL), and average ground flash density. For three sites, the most severe lightning events have been identified during the warm and cold months whereas the other two locations exhibit severe lightning detections mainly during the warm months. In this work severity is a measure of lightning observations per day. Statistics about the monthly exposure of the wind turbines are provided. In order to complement the analysis, meteorological parameters related to the lightning events were analysed. Radio sounding measurements provide an analysis of the condition of the atmosphere, in which an electrically charged thundercloud is formed. Furthermore, the reflectivity data from a radar station is used in order to identify convective cores, cloud shape and height of its top and base, and the motion direction of the thunderstorm clouds. With this approach, distinct differences between warm and cold season thunderstorms can be identified. In total, 27 severe thunderstorms events, which were detected by a LLS in the vicinity of the wind turbines, are investigated. The analysis of cold season thunderstorms shows that lightning discharges are triggered in a very big area over a long time period (up to 18 hours). As characteristic for cold season storms, the altitude of the charge separating -10◦ C isotherm is around 2000 meters above terrain and the wind velocity is above 12 meters per second. Warm season thunderstorms develop faster, and the overall lifetime of such an episode can vary from tens of minutes to several hours in the case of new storms being continuously developed in the same area. The distance of the charge separating -10◦ C and the ground is usually larger than 3000 meters. This analyse provides information about the different thunderstorm types which trigger lightning discharges on wind turbines.

A numerical simulation of sea breeze thunderstorm structure over the Hainan Island

Abstract: The land-sea breeze system is a wind pattern that is observed in coastal regionsIt is generated by the differences in the heat budgets of the land and sea surfacesThe role of the sea breeze circulation,including the sea breeze front,in triggering thunderstorm has long been recognizedThe afternoon thunderstorms triggered by sea breeze can affect the basic characteristics of the sea breeze and its changeIn this paper,the thunderstorm caused by sea breeze is called sea breeze thunderstormSurrounded by the sea,Hainan Island has strong sea breeze and rich water vapor under the influence of tropical oceanIt has a high incidence of sea breeze thunderstorm,which is triggered by interaction of local circulations such as land-sea breeze and mountain-valley breezeThe WRF-ARW model(Version 36)coupled with the Noah land surface is used to simulate the sea breeze thunderstorm over the Hainan Island during July 20,2012The characteristics of thunderstorm over complex terrain are analyzed with radar,satellite,sounding and surface observations dataThe structure and evolution of thunderstorm as well as its trigger mechanism are also discussedThis paper is intended to represent the mechanism of sea breeze thunderstormand improve the forecasting performanceAs a typical sea breeze thunderstorm day,there was a significant wind shift around the islandThe low-level sea breeze and land cover caused a unique water vapor distribution,which provided the conditions for local thunderstorm to produce precipitationThe convective instability layer emerged in the southern part of the island,which was conducive to the formation and development of the convective activityWhile the cold air in the north of island broke the unstable layer,the convection occurrence became more difficult in this regionAfter the sea breeze formed along the coast,it penetrated inland and developed graduallyBecause of the topography forcing,northern and southern sea breezes met in the vicinity of Baoting stationAs a result,a significant sea breeze convergence zone has formed,affecting local divergence and characteristics of vortexUnder the favorable dynamical condition,the local thunderstorm weather occurredWhen sea breeze thunderstorm over Hainan is discussed,we should not only concern with the development of the sea breeze front,but also need to analyze the local distribution of convective inhibitionThe evolution of local energy and convective parameters can indicate the arise of sea breeze thunderstorm in temporal and spatial scalesThe large convective available potential energy(CAPE)and small convective inhibition(CIN)have provided favorable conditions for the development of thunderstorm before it occurredAs the occurrence of thunderstorm,the instability energy was releasedThe CAPE decayed rapidly and the CIN began to riseIt was a symbol that thunderstorm system has entered into the decline stageThis study indicated that the characteristics of the sea breeze and thunderstorm can be reasonably simulated by WRF modelUnder the influence of the tropical ocean,the water vapor,convective potential energy and the level of free convection keep long-lasting development state which is favorable for the convectionThe convection would develop autonomously when the uplift produced by sea breeze convergence overcome the convective inhibition and reach free convection level,so the sea breeze convergence can often trigger thunderstorm in HainanThe sea breeze thunderstorm is closely related to the local terrain,which affects the spatial and temporal distributions of low-level wind and convection convergence zone This study is conducive to understand sea breeze thunderstorm over Hainan Island and the key factor to forecast it,but we still need further studies of more cases to support the relevant conclusion

A numerical study of hail process effects on charge structure and lightning flash rate of thunderstorms

Abstract: By use of French mesoscale non-hydrostatic numerical model Meso-NH, using two kinds of ice phase particles scheme: ICE3 scheme (no hail), ICE4 scheme (with hail), simulate the thunderstorm clouds charge structure, lightning flash rates to explore the impact of the hail process on the microphysical and electrical processes of the thunderstorm clouds. The results showed that: 1) ICE4 scheme of thunderstorm duration is shorter than ICE3 scheme, from ICE3 to ICE4, lightning flash rates display significantly reduced; 2) After addition of hail, thunderstorm cloud charge structure changes very little, charge density of ICE4 scheme significantly less than ICE3 scheme; 3) With the ICE4 scheme, lightning flash peak occurred after precipitation of hail.

Relations of lower atmosphere wind dynamics to synoptic conditions and weather phenomena

Abstract: Nonperiodic vertical and temporal variations in wind direction in the lower 500-meter air layer related to synoptic conditions are studied using the long-term data of acoustic remote sensing by the MODOS sodar at Moscow State University. Average values of wind shear to the right (clockwise) with time as a result of the passage of atmospheric fronts are 55° for cold fronts, 40° for warm fronts, and 45° for occlusion fronts. In some cases the clockwise wind shear may reach 180° per 30 minutes and 720° per several hours. The wind shear to the left with time is usually observed if the northern periphery of anticyclones or the ridge axis pass by. It takes more time than the clockwise wind shear does. Dramatic variations in wind direction with height including synchronous opposite air flows at different heights are observed in the zones of fronts, axes of ridges and troughs (if they are inclined), and cols. The vertical wind shear may reach 250° in the lower 300-meter air layer. Thunderstorms in Moscow are usually accompanied by the average wind speed increase by 1 m/s during 30-40 minutes after their beginning.