Wiebke Deierling

Estimation of total lightning from various storm parameters: A cloud‐resolving model study

[1] Because explicit prediction of the electrical activity in storms is computationally expensive and the processes are still poorly understood, an attractive way to predict lightning flash rates in numerical models is to rely on correlations between the flash rate and available model parameters. Predicted flash rates can be used for applications such as the parameterization to infer lightning‐produced nitrogen oxides. In this study, the potential for six model parameters (precipitation ice mass, ice water path, ice mass flux product, updraft volume, maximum vertical velocity, and cloud top height) to predict lightning rate has been investigated in a cloud‐resolving model framework. The Weather Research and Forecasting model (WRF) is used to simulate two different storms: the 10 July 1996 severe storm that occurred over the High Plains and the 13 July 2005 airmass thunderstorm near Huntsville, Alabama. It is shown that the WRF model reproduces the structure of the two storms. Results show that the maximum updraft velocity gives a good flash rate proxy for the severe storm. The ice mass flux product and precipitation ice mass can reproduce the flash rate trend but not the magnitude. The flash rate estimated from the cloud top height does not match the observed flash rate trend and value of the severe storm, but is in good agreement for the airmass thunderstorm. The ice water path predicts flash rate fairly well for the severe storm, but overpredicts it for the airmass thunderstorm. The updraft volume predicts flash rate poorly for both storms.

A method of estimating electric fields above electrified clouds from passive microwave observations

AbstractA unique dataset of coincident high-altitude passive microwave and electric field observations taken by the NASA ER-2 aircraft is used to assess the feasibility of estimating electric fields above electrified clouds using ubiquitous global and multidecadal satellite products. Once applied to a global dataset, such a product would provide a unique approach for diagnosing and monitoring the current sources of the global electric circuit (GEC).In this study an algorithm has been developed that employs ice scattering signals from 37- and 85-GHz passive microwave observations to characterize the electric fields above clouds overflown by the ER-2 aircraft at nearly 20-km altitude. Electric field estimates produced by this passive microwave algorithm are then compared to electric field observations also taken by the aircraft to assess its potential future utility with satellite datasets. The algorithm is shown to estimate observed electric field strengths over intense convective clouds at least 71% (58%)...

The Properties of Optical Lightning Flashes and the Clouds They Illuminate

Optical lightning sensors like the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) measure total lightning across large swaths of the globe with high detection efficiency. With two upcoming missions that employ these sensors – LIS on the International Space Station (ISS-LIS) and the Geostationary Lightning Mapper (GLM) on the GOES-R satellite – there has been increased interest in what these measurements can reveal about lightning and thunderstorms in addition to total flash activity. Optical lightning imagers are capable of observing the characteristics of individual flashes that include their sizes, durations, and radiative energies. However, it is important to exercise caution when interpreting trends in optical flash measurements because they can be affected by the scene. This study uses coincident measurements from the Tropical Rainfall Measuring Mission (TRMM) satellite to examine the properties of LIS flashes and the surrounding cloud regions they illuminate. These combined measurements are used to assess to what extent optical flash characteristics can be used to make inferences about flash structure and energetics. Clouds illuminated by lightning over land and ocean regions that are otherwise similar based on TRMM measurements are identified. Even when LIS flashes occur in similar clouds and background radiances, oceanic flashes are still shown to be larger, brighter, longer lasting, more prone to horizontal propagation and to contain more groups than their land-based counterparts. This suggests that the optical trends noted in literature are not entirely the result of radiative transfer effects, but rather stem from physical differences in the flashes.

Parameterizing total storm conduction currents in the Community Earth System Model

Electrified clouds are known to play a major role in the Global Electric Circuit. These clouds produce upward currents which maintain the potential difference between earths surface and the upper atmosphere. In this study, model output from two simulations of the Community Earth System Model (CESM) are compared with conduction currents and other data derived from the Tropical Rainfall Measuring Mission (TRMM) satellite, including both the lightning imaging sensor (LIS) and precipitation radar (PR). The intention is to determine CESMs skill at representing these microphysical and dynamical properties of clouds. Then, these cloud properties are used to develop a model parameterization to compute conduction currents from electrified clouds. Specifically, we evaluate the ability of global mean convective mass flux, ice water path and convective precipitation to represent conduction current sources. Parameterizations using these variables yield derived global mean currents that agree well with the geographical patterns of TRMM currents. In addition, comparing the diurnal variations of modeled global mean current to the observed diurnal variations of electric potential gradient, root mean square (RMS) errors range between 6.5% and 8.1%, but the maximum occurs 4 to 6 hours early in all three variables. Output currents derived from the model variables generally match well to the currents derived from TRMM, and the total global current estimates agree well with past studies. This suggests that cloud parameters are well suited for representing the global distribution and strength of currents in a global model framework.

Analysis of the diurnal variation of the global electric circuit obtained from different numerical models

This work analyzes different current source and conductivity parameterizations and their influence on the diurnal variation of the global electric circuit (GEC). The diurnal variations of the current source parameterizations obtained using electric field and conductivity measurements from plane overflights combined with global TRMM satellite data give generally good agreement with measured diurnal variation of the electric field at Vostok, Antarctica, where reference experimental measurements are performed. An approach employing 85-GHz passive microwave observations to infer currents within the GEC is compared and shows the best agreement in amplitude and phase with experimental measurements. To study the conductivity influence, GEC models solving the continuity equation in 3-D are used to calculate atmospheric resistance using yearly averaged conductivity obtained from the global circulation model CESM. Then, using current source parameterization combining mean currents and global counts of electrified clouds, if the exponential conductivity is substituted by the conductivity from CESM, the peak to peak diurnal variation of the ionospheric potential of the GEC decreases from 24% to 20%. The main reason for the change is the presence of clouds while effects of 222Rn ionization, aerosols and topography are less pronounced. The simulated peak to peak diurnal variation of the electric field at Vostok is increased from 15% to 18% from the diurnal variation of the global current in the GEC if conductivity from CESM is used.

A TRMM/GPM retrieval of the total mean generator current for the global electric circuit

A specialized satellite version of the passive microwave electric field retrieval algorithm (Peterson et al., 2015) is applied to observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) satellites to estimate the generator current for the Global Electric Circuit (GEC) and compute its temporal variability. By integrating retrieved Wilson currents from electrified clouds across the globe, we estimate a total mean current of between 1.4 kA (assuming the 7% fraction of electrified clouds producing downward currents measured by the ER-2 is representative) to 1.6 kA (assuming all electrified clouds contribute to the GEC). These current estimates come from all types of convective weather without preference, including Electrified Shower Clouds (ESCs). The diurnal distribution of the retrieved generator current is in excellent agreement with the Carnegie curve (RMS difference: 1.7%). The temporal variability of the total mean generator current ranges from 110% on semi-annual timescales (29% on an annual timescale) to 7.5% on decadal timescales with notable responses to the Madden-Julian Oscillation and El Nino Southern Oscillation. The geographical distribution of current includes significant contributions from oceanic regions in addition to the land-based tropical chimneys. The relative importance of the Americas and Asia chimneys compared to Africa is consistent with the best modern ground-based observations and further highlights the importance of ESCs for the GEC.

Colorado Plowable Hailstorms: Synoptic Weather, Radar, and Lightning Characteristics

AbstractSynoptic weather, S-band dual-polarization radar, and total lightning observations are analyzed from four thunderstorms that produced “plowable” hail accumulations of 15–60 cm in localized areas of the Colorado Front Range. Results indicate that moist, relatively slow (5–15 m s−1) southwesterly-to-westerly flow at 500 hPa and postfrontal low-level upslope flow, with 2-m dewpoint temperatures of 11°–19°C at 1200 LST, were present on each plowable hail day. This pattern resulted in column-integrated precipitable water values that were 132%–184% of the monthly means and freezing-level heights that were 100–700 m higher than average. Radar data indicate that between one and three maxima in reflectivity Z (68–75 dBZ) and 50-dBZ echo-top height (11–15 km MSL) occurred over the lifetime of each hailstorm. These maxima, which imply an enhancement in updraft strength, resulted in increased graupel and hail production and accumulating hail at the surface within 30 min of the highest echo tops. The hail core...

Detecting Convective Induced Turbulence via Total Lightning Sensing

In this paper, we research a prototype Convective-Induced Turbulence (CIT) hazard detection system for commercial aviation based on Total Lightning Sensing (TLS) as an indicator of the location and severity of in-cloud CIT. Total lightning is the combination of Cloud-to-Ground (CG) and In-Cloud (IC) lightning, and has been shown to correlate well with storm dynamics. Total lightning activity will be measured globally at high temporal resolution from total lightning detectors onboard future geostationary satellites. We investigate the relationship between IC convective turbulence and total lightning measurements, and determine the skill of total lightning as an indicator of in-cloud CIT. Our design is based on existing satellite-based data; we will not mount any new hardware or software onboard any aircraft, so we avoid high implementation costs related to airborne measurement systems. Our solution has the potential of enhancing the safety of flight for aircraft in the Continental United States (CONUS) as well as over oceanic airspaces (where currently no CIT information is available for commercial aviation).

Retrieving Global Wilson Currents from Electrified Clouds using Satellite Passive Microwave Observations

AbstractHigh-altitude atmospheric electricity measurements have been used to calculate the conduction (Wilson) currents that are supplied to the global electric circuit (GEC) by individual electrif...

Relationships Between Lightning and Convective Turbulence

Total lightning has been shown to correlate well with thunderstorm dynamics. Thus, correlations may exist between in-cloud convective turbulence and total lightning activity. Over the continental United States, the NEXRAD Turbulence Detection Algorithm (NTDA) provides three-dimensional (3D) fields of in-cloud Eddy Dissipation Rate (EDR), which is a quantitative measure of turbulence. Comprehensive total lightning measurements are available in some regions of the United States such as in Northern Colorado and New Mexico. Herein, investigations of the temporal and spatial relationships of 3D total lightning and NTDA EDR measurements for non-severe single cell thunderstorms in New Mexico and severe storms in Colorado are described. Results suggest that the occurrence of moderate or greater turbulence at upper levels of storms is related to storm total lightning flash rate, though exact relationships depend on the storm type. Areas of moderate and greater turbulence are also observed to coincide with the footprint of horizontal lightning flash extents. Time series show that lighter turbulence begins to occur prior to lightning initiation in the storms and also extends past the storm’s lightning activity. Furthermore, trends of storm total moderate or greater turbulence are correlated to storm total lightning flash rate and extent. These observations are consistent with other recent studies by the authors and others that suggest that total lightning may be useful in diagnosing areas of potentially hazardous atmospheric turbulence. With the expected advent of geostationary satellite based lightning mapping in the next few years, possible relationships between lightning and turbulence characteristics might provide useful information to aviation users, particularly in oceanic or remote areas where ground-based Doppler weather radar observations are unavailable.