Multi-Sensor Field Studies of Lightning and Implications for MTG-LI

Future geostationary satellite systems will offer a variety of improved observing capabilities which will be extremely useful for many applications like numerical weather forecasting, nowcasting of severe weather, climate research or hydrology. The planning for MTG (Meteosat Third Generation) includes an optical lightning imager (LI) as part of the payload. One requirement for a proper interpretation of these optical data is a better understanding of what components of a flash are to be seen from space and how these observations relate to ground based radio frequency observations. Therefore, the objectives of the present study concern the improvement of the understanding of the complex lightning process which then enables a proper interpretation of the optical data. For assessing the future performances and benefits of a geostationary lightning sensor this study takes advantage of the comprehensive lightning data sets obtained from the recent CHUVA field experiment performed in Brazil. (CHUVA - Cloud processes of tHe main precipitation systems in Brazil: A contribUtion to cloud resolVing modeling and to the GPM (GlobAl Precipitation Measurement)). During the rainy season of 2011-2012 a large number of ground based lightning detection systems was set up in the Sao Paulo area in Brazil. In the present study we look at the detailed radio frequency (RF) based observation from LINET (Lightning detection network operated by DLR, nowcast and USP) and observing strokes in the VLF/LF (very low and low frequency) range, the LMA (Lightning mapping array) from NASA observing RF sources in the VHF (very high frequency) range and the TRMM-LIS (Tropical Rainfall Measuring Mission-Lightning Imaging Sensor) optical space borne lightning imager. The LIS is used as a reference instrument for the future MTG-LI sensor as well as for the corresponding GLM sensor (Geostationary Lightning Mapper) on GOES-R. Thus it is possible to study the relations between the RF and optical signals from lightning in detail and to assess the performance of the future geostationary observations from a set of proxy satellite data generated from the ground based observations. In confirmation of previous studies, it was found that often a direct temporal coincidence of RF signals (LINET strokes) and optical pulses (LIS groups) exists. The short baseline configuration of LINET allowed to observe the strokes mapping the flash branches similar to LMA, but by locating the limited number of strong cloud strokes rather than a large number of weak source points from leader steps. An initial breakdown phase of vertically propagating sources can often be found in LINET and LMA data. The higher level LINET and LMA signals have higher probability to be optically detected. Lower level LINET and LMA signals are optically detected from above in case of missing high level precipitation as inferred from radar observations provided by USP. The new comprehensive data set allows for constructing proxy data for the future geostationary lightning mappers

The CHUVA Lightning Mapping Campaign

The primary science objective for the CHUVA lightning mapping campaign is to combine measurements of total lightning activity, lightning channel mapping, and detailed information on the locations of cloud charge regions of thunderstorms with the planned observations of the CHUVA (Cloud processes of tHe main precipitation systems in Brazil: A contribUtion to cloud resolVing modeling and to the GPM (GlobAl Precipitation Measurement) field campaign. The lightning campaign takes place during the CHUVA intensive observation period October-December 2011 in the vicinity of S o Luiz do Paraitinga with Brazilian, US, and European government, university and industry participants. Total lightning measurements that can be provided by ground-based regional 2-D and 3-D total lightning mapping networks coincident with overpasses of the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (LIS) and the SEVIRI (Spinning Enhanced Visible and Infrared Imager) on the Meteosat Second Generation satellite in geostationary earth orbit will be used to generate proxy data sets for the next generation US and European geostationary satellites. Proxy data, which play an important role in the pre-launch mission development and in user readiness preparation, are used to develop and validate algorithms so that they will be ready for operational use quickly following the planned launch of the GOES-R Geostationary Lightning Mapper (GLM) in 2015 and the Meteosat Third Generation Lightning Imager (LI) in 2017. To date there is no well-characterized total lightning data set coincident with the imagers. Therefore, to take the greatest advantage of this opportunity to collect detailed and comprehensive total lightning data sets, test and validate multi-sensor nowcasting applications for the monitoring, tracking, warning, and prediction of severe and high impact weather, and to advance our knowledge of thunderstorm physics, extensive measurements from lightning mapping networks will be collected in conjunction with electric field mills, field change sensors, high speed cameras and other lightning sensors, dual-polarimetric radars, and aircraft in-situ microphysics which will allow for excellent cross-network inter-comparisons, assessments, and physical understanding

Characterization of dynamic of convection: a case study from the COPS experiment

The life cycle of deep convection is investigated with emphasis on their dynamical evolution. The data used in this study are from the COPS campaign (Convective and Orographically-induced Precipitation Study) that took place in southwestern Germany and eastern France in the summer 2007. On the basis of case study from 15th July the convection is described from convective initiation at 14:30 UTC to the decay around 16:30 UTC. The convective initiation is identified by significantly changing of brightness temperature of the MSG (Meteosat Second Generation satellite) rapid scan data at visible channel (10.8µm). The dynamic evolution during the life cycle can be described by the horizontal wind field in different altitude stages. Therefore radar data of four different sites were used, namely the operational radars of the German weather service (DWD) at Feldberg and Tuerkheim, C-band radar at Karlsruhe provided by the Institute for Meteorology and Climate Research (IMK), and the polarimetric radar POLDIRAD provided by the Institut für Physik der Atmosphäre (DLR), Oberpfaffenhofen which was situated at Waltenheim sur Zorn (France) during the COPS campaign. While radar scan time was not synchronized ten minute time frames were selected before gridding all data to a common volume and processing by using multiple Doppler method. The estimated wind fields are compared with surface wind from VERA (Vienna Enhanced Resolution Analysis) of the University of Vienna and calculations from the Meso-NH model. To investigate microphysical processes different types of hydrometeors were classified by using polarimetric information of the DLR radar POLDIRAD. In combination with 3D- lightning data, provided by the European lightning network LINET, the electrical activity of the cells are reconstructed. The type and mass density of hydrometeors are also compared with the output from model calculation by using Meso-NH model

Characterization of the life cycle of convection from initiation to decay on the basis of case study from July, 15th 2007

The life cycle of convection from its initiation to the decay is described in detail for a case study on July, 15th 2007 during the COPS (Convective and Orographically-induced Precipitation Study) campaign. The convective initiation on July, 15th is identified for the time step 14:30 – 14:40 UTC. In this time interval the brightness temperature of the MSG rapid scan data at 10.8 µm changed significantly (<-4 K/min) while radar reflectivity reaches values over 35 dBZ and lightning activity starts (first event at 14:34 UTC). To assess the dynamic evolution during the mature state of the cell wind field was estimated by using dual doppler method. Therefore the radar data from the DLR POLDIRAD and the Feldberg radar were combined. To investigate microphysical processes different types of hydrometeors were classified by using polarimetric information of the DLR radar POLDIRAD. In combination with 3D- lightning data, provided by the European lightning network LINET, the electrical activity of the cells were reconstructed. The decay process appears slower and less pronounced than the initiation process. Last lightning event was observed at 14:45 UTC while radar reflectivity decreases to values below 35 dBZ until 15:40 UTC and the brightness temperature remains below 250 K until 16:30 UTC

The temporal evolution of three-dimensional lightning parameters and their suitability for thunderstorm tracking and nowcasting

Total lightning (TL) data have been found to provide valuable information about the internal dynamics of a thunderstorm allowing conclusions about its further development as well as indicating potential of thunderstorm-related severe weather at the ground. This paper investigates electrical discharge correlations of strokes and flashes with respect to the temporal evolution of thunderstorms in case studies as well as by statistical means. The recently developed algorithm li-TRAM (tracking and monitoring of lightning cells, Meyer et al., 2013) has been employed to track and monitor thunderstorms based on three-dimensionally resolved TL data provided as stroke events by the European lightning location network LINET. From statistical investigation of 863 suited thunderstorm life cycles, the cell area turned out to correlate well with (a) the total discharge rate, (b) the in-cloud (IC) discharge rate, and (c) the mean IC discharge height per lightning cell as identified by li-TRAM. All three parameter correlations consistently show an abrupt change in discharge characteristics around a cell area of 170 km2. Statistical investigations supported by the comparison of three case studies – selected to represent a single storm, a multi-cell and a supercell – strongly suggest that the correlation functions include the temporal evolution as well as the storm type. With the help of volumetric radar data, it can also be suggested that the well-defined break observed at 170 km2 marks the region where the transition occurs from short-lived and rather simple structured single storm cells to better organized, more persistent, and more complex structured thunderstorm forms, e.g. multi-cells and supercells. All three storm types experience similar discharge characteristics during their growing and dissipating phases. However, while the poorly organized and short-lived cells preferentially remain small during a short mature phase, mainly the more persistent thunderstorm types develop to sizes above 170 km2 during a pronounced mature stage. At that stage they exhibit on average higher discharge rates at higher altitudes as compared with matured single cells. With the maximum stroke distance set to 10 km and a flash duration set to 1 s, the parameterization functions found for the stroke rate as a function of the cell area have been transformed to a flash rate. The presented study suggests that, with respect to the storm type, stroke and flash correlations can be parameterized. There is also strong evidence that parameterization functions include the time parameter, so that altogether TL stroke information has good potential to pre-estimate the further evolution (nowcast) of a currently observed storm in an object-oriented thunderstorm nowcasting approach

Modeling the Flash Rate of Thunderstorms. Part II: Implementation

In Part I of this two-part paper a new method of predicting the total lightning flash rate in thunderstorms was introduced. In this paper, the implementation of this method into the convection-permitting Consortium for Small Scale Modeling (COSMO) model is presented. The new approach is based on a simple theoretical model that consists of a dipole charge structure, which is maintained by a generator current and discharged by lightning and, to a small extent, by a leakage current. This approach yields a set of four predictor variables, which are not amenable to direct observations and consequently need to be parameterized (Part I). Using an algorithm that identifies thunderstorm cells and their properties, this approach is applied to determine the flash frequency of every thunderstorm cell in the model domain. With this information, the number of flashes that are accumulated by each cell and during the interval between the activation of the lightning scheme can be calculated. These flashes are then randomly distributed in time and beneath each cell. The output contains the longitude, the latitude, and the time of occurrence of each simulated discharge. Simulations of real-world scenarios are presented, which are compared to measurements with the lightning detection network, LINET. These comparisons are done on the cloud scale as well as in a mesoscale region composing southern Germany (two cases each). The flash rates of individual cumulonimbus clouds at the extreme ends of the intensity spectrum are realistically simulated. The simulated overall lightning activity over southern Germany is dominated by spatiotemporal displacements of the modeled convective clouds, although the scheme generally reproduces realistic patterns such as coherent lightning swaths

Modeling the Flash Rate of Thunderstorms. Part I: Framework

In this study a straightforward theoretical approach to determining the flash rate in thunderstorms is presented. A two-plate capacitor represents the basic dipole charge structure of a thunderstorm, which is charged by the generator current and discharged by lightning. If the geometry of the capacitor plates, the generator-current density, and the lightning charge are known, and if charging and discharging are in equilibrium, then the flash rate is uniquely determined. To diagnose the flash rate of real-world thunderstorms using this framework, estimates of the required relationships between the predictor variables and observable cloud properties are provided. With these estimates, the flash rate can be parameterized. In previous approaches, the lightning rate has been set linearly proportional to the electrification rate (such as the storm�s generator power or generator current), which implies a constant amount of neutralization by lightning discharges (such as lightning energy or lightning charge). This leads to inconsistencies between these approaches. Within the new framework proposed here, the discharge strength is allowed to vary with storm geometry, which remedies the physical inconsistencies of the previous approaches. The new parameterization is compared with observations using polarimetric radar data and measurements fromthe lightning detection network, LINET. The flash rates of a broad spectrumof discrete thunderstorm cells are accurately diagnosed by the new approach, while the flash rates of mesoscale convective systems are overestimated