Electric Fields, Cloud Microphysics, and Reflectivity in Anvils of Florida Thunderstorms

A coordinated aircraft - radar project that investigated the electric fields, cloud microphysics and radar reflectivity of thunderstorm anvils near Kennedy Space Center is described. Measurements from two cases illustrate the extensive nature of the microphysics and electric field observations. As the aircraft flew from the edges of anvils into the interior, electric fields very frequently increased abruptly from approx.1 to >10 kV/m even though the particle concentrations and radar reflectivity increased smoothly. The abrupt increase in field usually occurred when the aircraft entered regions with a reflectivity of 10 to 15 dBZ. It is suggested that the abrupt increase in electric field may be because the charge advection from the storm core did not occur across the entire breadth of the anvil and was not constant in time. Screening layers were not detected near the edges of the anvils. Some long-lived anvils showed subsequent enhancement of electric field and reflectivity and growth of particles, which if localized, might be a factor in explaining the abrupt change of field in some cases. Comparisons of electric field magnitude with particle concentration or reflectivity for a combined data set that included all anvil measurements showed a threshold behavior. When the average reflectivity, such as in a 3-km cube, was less than approximately 5 dBZ, the electric field magnitude was <3 kV/m. Based on these findings, the Volume Averaged Height Integrated Radar Reflectivity (VAHIRR) is now being used by NASA, the Air Force and Federal Aviation Administration in new Lightning Launch Commit Criteria as a diagnostic for high electric fields in anvils

Sub-millimetre wave radiometry for cloud and rain characterization: From simulation to Earth observation mission concept

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Assimilation of satellite lightning data in a storm-scale numerical weather prediction system using a 3D-EnVar data assimilation scheme

International audienceAbstract The objective of this study is to prepare the assimilation of the Meteosat Third Generation Lightning Imager (MTG-LI) observations in the regional numerical weather prediction model AROME-France using a 3D-EnVar data assimilation algorithm. As opposed to the current operational configuration of AROME-France data assimilation system, the hydrometeor specific contents are added in the control variable and are thus updated during the assimilation process. Consequently, a lightning observation operator based on the specific contents of snow and graupel is used. As the first MTG satellite was launched in December 2022, the real MTG-LI observations are not available yet, and proxy space-borne lightning observations generated from ground-based lightning detection network are used. We assess the forecast skills of experiments assimilating lightning in a close to operational configuration by comparing the results to a reference experiment that does not assimilate lightning. In the studied cases, the frequency bias and fraction skill score are improved for brightness temperatures forecasts lower than 280 K up to 4 hours after the assimilation, implying a better description of the general cloud cover. The convective cores, identified by brightness temperatures lower than 220 K, are better captured in the first forecast hour but this improvement is not maintained through time and quickly fades

Numerical study of a heavy precipitation event over southern France, in the frame of HYMEX project: Observational analysis and model results using assimilation of lightning

International audienceHere, a heavy precipitation event that affected Southern France in the period of 6–8 September 2010 is studied. This event produced more than 300 mm in a 24-h period and resulted in floods in an area that has been often affected by similar events during autumn.The system has been monitored by in situ surface stations, radar, lightning networks and satellites that put into evidence the anchoring of convective cells along mountainous areas. The precipitation episode was simulated using the MM5 non-hydrostatic model at very high resolution. Moreover, an assimilation technique has been applied that controls the activation of the convective parameterisation scheme using lightning data as a proxy for the presence of convection. The assimilation of lightning proved to have a positive impact on the representation of the precipitation field, providing also more realistic positioning of the precipitation maxima, mainly during the second day of the event. The improvement of the model simulation when lightning was assimilated was quantitatively supported by the verification against observations.The improvement of monitoring, understanding and forecasting of such type of events is in line with the scientific topics prescribed within HYMEX international project

An optical lightning simulator in an electrified Cloud Resolving Model as a support of future lightning observation missions

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A satellite lightning observation operator for storm-scale numerical weather prediction

International audienceThis study aims at simulating satellite-measured lightning observations with numerical weather prediction (NWP) system variables. A total of eight parameters, calculated with the AROME-France NWP system variables, were selected from a literature review to be used as proxies for satellite lightning observations. Two different proxy types emerged from this literature review: microphysical and dynamical proxies. Here, we investigate which ones are best related to satellite lightning and calibrate an empirical relationship between the best parameters and lightning data. To obtain those relationships, we fit machine learning regression models to our data. In this study, pseudo flash extent accumulation (FEA) observations are used because no actual geostationary lightning observations are available yet over France, and non-geostationary satellite lightning data represent a sample that is too small for our study. The performances of each proxy and machine learning regression model are evaluated by computing fractions skill scores (FSSs) with respect to observed FEA and proxy-based FEA. The present study suggests that microphysical proxies are more suited than the dynamical ones to model satellite lightning observations with the AROME-France NWP system. The performances of multivariate regression models are also evaluated by combining several proxies after a feature selection based on a principal component analysis and a proxy correlation study, but no proxy combination yielded better results than microphysical proxies alone. Finally, different accumulation periods of the FEA had little influence, i.e. similar FSS, on the regression model's ability to reproduce the observed FEA. In future studies, the microphysical-based relationship will be used as an observation operator to perform satellite lightning data assimilation in storm-scale NWP systems and applied to NWP forecasts to simulate satellite lightning data

Explicit simulation of electrified clouds: From idealized to real case studies

International audienceOriginal results obtained with the revised version of the explicit cloud electrification module developed in the French mesoscale model MesoNH are presented. The module includes three ingredients: (i) a prognostic budget equation of the electric charges carried by each type of hydrometeor and by the positive and negative ions, (ii) a computation of the electric field by inverting the Gauss equation and (iii) a statistical algorithm to produce intra-cloud and cloud-to-ground discharges. Electric charges are generated by non-inductive (NI) processes involving ice particles that collide in the presence of supercooled water. The geometry of the lightning flashes obeys a fractal law that characterizes the densely branched flash structures with a marked horizontal extent in electrically charged regions of the clouds.For the first time, the electrical module of MesoNH is used to simulate the electrical aspects of a heavy precipitation event over the Cevennes area in the South of France. MesoNH is initialized with "AROME" analyses of Meteo-France for the 6-8 September 2010 event that produced locally 250 to 300 mm of precipitation over the Cevennes ridge. A 54 hour simulation starting 6 September 2010 at 00 UTC and without electricity, is performed at 1 km resolution over a 384 × 384 km2 area in order to check the ability of the model to reproduce the very fine scale structure of the rainfall. MesoNH is then restarted on 7 September 2010 at noon for a 6 hour simulation involving the full electrical module. Several aspects of the electrical state of the clouds could be simulated at this scale: the cloud charge structure, the electric field and the lightning flash characteristics. Finally a map of flash density is compared to observations taken from two conventional detection networks (LInet and ATDnet). Both networks suggest that the model produces ten times too many flashes but arguments are put forward to explain this discrepancy, e.g., filtering the less energetic flashes improves the comparison. In conclusion, this study calls for a reference evaluation of the electrical module of MesoNH against statistics of flash data at high resolution in a next planned field experiment in 2012

Explicit simulations of electrified mixed-phase clouds in MesoNH: from semi-idealized to first real-case studies

International audienceCommunication about Explicit simulations of electrified mixed-phase clouds in MesoNH: from semi-idealized to first real-case studie

Relationships between lightning activity, microphysics and kinematics in thunderclouds: a case study observed by S and C band radars in the South of France (HyMeX SOP area)

International audienceCommunication about Relationships between lightning activity, microphysics and kinematics in thunderclouds: a case study observed by S and C band radars in the South of France (HyMeX SOP area

Natural lightning flashes: from observation to modelling

National audienceCommunication about Natural lightning flashes: from observation to modellin