1. Thunderstorm Charge Structures Producing Negative Gigantic Jets
Levi Boggs1 Ningyu Liu1, and Hamid K. Rassoul1
1Geospace Physics Laboratory, Physics and Space Sciences Department, Florida Institute of Technology, Melbourne, FL, USA
Abstract
Common Storm Features Observed During GJs
Evolution of Charge Structure
Lightning discharges that escape the upper region of the thundercloud and travel upward to the lower ionosphere (80 km) are known as gigantic jets [Pasko et al., Nature, 416, , 2002; Su et al, Nature, 423, , 2003]. They often are produced by oceanic storms [Chen et al., JGR, 1113, A08306, 2008] and are usually of negative polarity, transferring negative charge upward. These discharges electrically couple the upper troposphere and the lower ionosphere. Gigantic jets are often very powerful and have been found to transfer very large amounts of charge to the ionosphere on a timescale of hundreds of milliseconds to seconds [Liu et al., Nat. Commn., 6, 5995, 2015].The typical thunderstorm has a tripolar charge structure, with large upper positive charge, large middle negative charge, and small lower positive charge. An upper negative screening layer can also be found at the upper thundercloud boundary [Krehbiel et al., Nat. Geosci., 1, , 2008; Riousset et al., JGR, 115, A00E10, 2010]. Most lightning discharges are intracloud (IC) flashes between the upper and middle charge regions. However, if the upper positive charge region is weakened, then an IC flash can escape the upper positive charge and become a gigantic jet [Krehbiel et al., 2008; Riousset et al., 2010]. This takes place when the upper negative screening layer mixes with the upper positive charge, resulting in a charge imbalance between the middle negative and upper positive charge regions. Gigantic jets have been found in environments that exhibit strong external wind shear near the upper thundercloud boundary [Lazarus et al., JGR Atmos., 120, , 2015]. This strong wind shear likely aids in mixing the upper negative screening layer with the upper positive charge, facilitating the formation of gigantic jets. The work we present here includes a detailed charge structure analysis of four gigantic jet producing thunderstorms. The analysis involves combining dual-polarization radar, very high frequency and low frequency lightning, and balloon radiosonde data. Our results show that the charge structure of the gigantic jet producing thunderstorms is very different from the typical tripolar thunderstorm charge structure. We will discuss what meteorological processes form these charge structures and what makes them unique. a b c
Each GJ was observed during a convective ’pulse’
The convective pulses consisted of a brief, very intense updraft . 3 6 9 12 15 a) c) b) d) 1
Florida 2013 3 6 9 12 15 2 3
Florida 2014
Figure 3. Charge structure (overlaid on radar vertical cross sections) determined by the propagation of lightning leaders detected by VHF LDAR data for the Florida 2010 case during the (a) pre-pulse (b) initial pulse (c) final-pulse (gigantic jet) and (d) post-GJ times. The white (black) points denote upper positive (middle negative) charge and the blue vertical lines in (c) denote the edges of the updraft surrounded by large spectrum width, as seen in Figure 2, row 7, column c. The vertical scale is in km.
Introduction 3 6 9 12 15 4
Gigantic jets (GJ) are lightning discharges that escape the top of thunderclouds and propagate to the lower ionosphere
The common thunderstorm has a tripolar charge structure with large, wide upper positive and middle negative charge regions, a small lower positive charge region, and a negative screening layer at the top of the thundercloud
Previous fractal modeling studies simulating GJs used charge structures similar to the classic tripolar charge structures – with a reduced upper positive charge [Krehbiel et al., 2008; Riousset et al., 2010].
Large, wide upper positive charge region before the convective pulse.
During convective pulse, rapid charging inside intense updraft. Upper positive charge elevates.
Near the end of the convective pulse, the upper positive charge is greatly reduced in magnitude, and the upper positive charge region is very narrow and reaches its highest elevation.
After the convective pulse, the upper positive charge widens again and starts to subside.
The convective pulse is short-lived, and the GJ charge structure exists for a short time (2-3 minutes). 5
Oklahoma
2010
Time (UTC)
Horizontal Standard Deviation
Vertical Standard Deviation
Vertical Mean Position
# LDAR points
In U.P. charge region
# Flashes
Pre-Pulse
10:45: :46:30 UTC
12.77 km
1.18 km
11.54 km
594 5
Initial Pulse
10:57: :58:46 UTC
2.94 km
1.52 km
11.73 km
635 8
Final-Pulse (GJ)
11:00: :01:35 UTC
1.57 km
1.11 km
13.2 km 97 6
Post GJ
11:04: :05:19 UTC
6.38 km
1.31 km
12.98 km
762 3 6 9 12 15 6
Table 1. Parameters describing the upper positive charge shown in Figure 3. 7
Conclusions
Figure 1. (Left) Gigantic jet observation from Liu et al. [2015]. (Middle) Classic tripolar charge structure for a small thunderstorm identified from lightning mapping array (LMA) observations [Krehbiel et al., 2008]. (Right) Fractal simulation of a GJ from Riousset et al. [2010].
Florida 2010
The thunderstorm charge structure during GJs features a narrow, elevated upper positive charge region over a wide middle negative charge region – different from the classic tripolar thunderstorm charge structure.
This charge structure is driven by an intense convective pulse with strong storm top divergence, which creates heavy turbulence around the updraft.
The storm top divergence pushes the upper negative screening layer radially outward from the updraft center, and strong external winds mix the negative screening charge with upper positive charge outside the updraft.
This charge structure exists for a short amount of time and may explain why there are so few observations of GJs. 3 6 9 12 15 8
Methods and Data
We analyzed four convective systems that produced nine GJs
Weather Surveillance Radar 88-Doppler (WSR-88D) data provided insight into the storm structure and turbulent mixing
Base Reflectivity (Z): aided in identifying storm updrafts and general storm structure
Base Velocity (BV): provided information about storm top divergence
Spectrum Width (SW): provided information about turbulent mixing near the storm top
Very High Frequency (VHF) lightning data (Lightning Detection and Ranging System [LDAR])
Allowed lightning discharges to be mapped in three dimensions and aided in identifying thundercloud charge regions
Low Frequency (LF) lightning data (National Lightning Detection Network [NLDN])
Provided the latitude and longitude of intracloud (IC) discharges associated with each GJ 10 45 80
dBZ
-70 70 1 12 22
kts
kts
References and Acknowledgements
Figure 2. (Column a) Base Reflectivity (Column b) Base Velocity and (Column c) Spectrum Width during times of GJs. The odd panels are horizontal elevation angles showing the upper (10-14 km) regions of the thunderstorms. The even panels are vertical cross sections taken along the white lines in the odd panels, with the vertical scale in km. The vertical blue lines in the even panels mark the positions of the NLDN IC flashes associated with each GJ. The black points (blue points) in rows 5 and 7 (6 and 8) are VHF points associated with each parent GJ flash.
Pasko, V. P., Stanley, M. A., Matthews, J. D., Inan, U. S. & Wood, T. G. Electrical discharge from a thundercloud top to the lower ionosphere. Nature 416, 152–154 (2002).
Su, H. T. et al. Gigantic jets between a thundercloud and the ionosphere. Nature 423, 974–976 (2003).
Chen, A. B. et al. Global distributions and occurrence rates of transient luminous events. J. Geophys. Res. 113, A08306 (2008).
Krehbiel, P. R., J. A. Riousset, V. P. Pasko, R. J. Thomas, W. Rison, M. A. Stanley, and H. E. Edens (2008), Upward electrical discharges from thunderstorms, Nat. Geosci., 1, 233–237, doi: /ngeo162.
J. A. Riousset, V. P. Pasko, P. R. Krehbiel, W. Rison, and M. A. Stanley. (2010b) Modeling of thundercloud screening charges: Implications for blue and gigantic jets. J. Geophys. Res., 115:A00E10, doi: /2009JA
N. Y. Liu, N. Spiva, J. R. Dwyer, H. K. Rassoul, D. Free, and S. A. Cummer. (2015) Upward electrical dischargesobserved above Tropical Depression Dorian. Nat. Commun., 6:5995, 2015b. doi: /ncomms6995.
S.M. Lazarus, M.E. Splitt, J.Brownlee, N. Spiva, and N. Liu. (2015)A thermodynamic, kinematic and microphysical analysis of a jet and gigantic jet-producing florida thunderstorm. J. Geophys. Res.,: Atmospheres, 2015.
Each storm is very intense - altitude of 30 dBZ reflectivity
Strong storm top divergence is present in all cases
Large amounts of turbulent mixing around the updraft
I would like to thank Gaopung Lu for providing the VHF data. This research was supported in part by NSF grants AGS and AGS to the Florida Institute of Technology.