Observations of TLEs in winter thunderstorms during the ILAN campaigns Yoav Yair 1, Colin Price 2, Michal Ganot 2, Eran Greenberg 2, Roy Yaniv 1,2, Yosef Sherez 2, Baruch Ziv 1, Na’ama Reicher 2, Elyakom Vadislavsky 3, Carynelissa Erlick 3 and Adam Devir 1,4 1 The Open University of Israel 2 Tel-Aviv University 3 Hebrew University of Jerusalem 4 IARD, Nesher

Talk Layout Winter thunderstorms - Refresher The ILAN winter campaigns –Single station observations –Two-Station observations 2007/8 –ELF and VLF data Main Results Optical properties Meteorological conditions Calibrated measurements 3D structure Summary Future Research

Winter thunderstorms - climatology Occur in very few places in Northern Hemisphere winter, mostly where cold air is transported above warm water Gulf Stream, Sea of Japan, Mediterranean Sea Land areas are almost completely devoid of thunderstorm activity

Winter Sprites (refresher) So far, TLEs above winter thunderstorms have been observed exclusively in Japan (Fukunishi et al., GRL, 1999; Takahashi et al., JASTP, 2003; Hobara et al., 2003; Hayakawa et al., JGR, 2004; Adachi et al., GRL, 2004 and many newer papers) In Japan, TLEs are found in the winter monsoon regime, when cold Siberian air-masses flow from north-east above the warm Sea of Japan. The ensuing instability leads to the development of active Cumulonimbus clouds with a vertical dimension of 5-7km, embedded within larger (8,000-40,000km 2 ) stratiform-like regions The analogy between the synoptic setting for winter thunderstorms in Japan and in the Eastern Mediterranean has already been noted (Levin et al., GRL, 1996; Yair et al., JGR, 1998; Altaratz et al., MWR, 2003) – cold air-masses from Europe move over the warm Mediterranean Sea.

ILAN winter campaigns (ISF, ) We observe storms and cold-fronts west of Israel as they approach the coast 2003/4 Season – testing and system validation 2004/5Season – Initial observations from Tel-Aviv –No GPS, No tracking 2005/6 Season observations from TAU and MR 2006/7 and 07/08 Seasons – two stations, also East! Cameras: Watec100N with a 12mm f/0.8 lens (PAL) FOV of 31.5˚x23 Watec-902H with a 25mm f/1.4 lens (NTSC) FOV of 14˚x10.5˚ Real time event-detection software (UFO Capture), GPS time- stamp ELF and VLF data from Negev stations (MR, SB), NCK in Hungary Weather radar – real time, locating active cells (dBZ) Weather forecast – decision on observation site based on viewing conditions as a function of cloud coverage Real-Time target acquisition based on BOLTEK lightning detection system TAU) and IR satellite images, also weather radar

Tel-Aviv or Wise Observatory, Mizpe Ramon

Sites in the Negev Desert (Israel) Mitzpe Ramon (ELF) Sde-Boker (VLF) Geo-location of the parent lightning (Price et al., 2001; Greenberg et al, 2004).

GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L12801, doi: /2007G L029258, 2007 Satellite analysis: 13Jan06 12z USAFE OWS WebSite Estofex: In 4 different winter storms we detected 30 events: 26 sprites and 4 elves. The detection ranges varied from 250 to 450 km. Sprites were found to be produced exclusively by +CGs that can be traced to active cells with a vertical dimension of 5–7 km and cloud top temperature of minus 40C, embedded in a much larger matrix of stratiform cloudiness.

date (MR) (MR) (TA) (TA) Total sprites elves total Type# of eventsDistribution Column (single)27.7% Column (group)1142.3% Carrot (single)311.5% Carrot (group)623% Undefined415.5% ELF: All events have Qds between Qkm, related to +CG

Diffused light from cloud top Sprite β Cepheus Mag α Cepheus Mag µ Cepheus Mag ε Draco Mag Observations from the desert: clean sky, very low light pollution Asymmetric Elves brightness

Combined radar and satellite image analysis for events with location of parent flash based on LPATS Sprites appear in areas with moderate reflectivity in the trailing part of the cold front, not necessarily associated with the highest cloud-tops

 Enhanced convection associated with the left side of the exit of a jet streak Synoptic: conditions for sprite-producing thunderstorms  Shallow upper-level trough with a weak surface low near Cyprus  Deep cyclone near Crete accompanied by upper level divergence, associated with positive vorticity advection ahead of the trough

Time delay between ELF transient from the parent flash and the Optically observed sprite: shorter delay for columns Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 1569– TLEs in 24 minutes. All events were preceded by a clear transient in the SR band, indicating a +CG parent lightning

4 examples for non-TLEs producing CGs that occurred a few tens of seconds before and after SP+CG. No significant difference found compared to SP+CG! Averaged (characteristic) spectral waveforms in frequency for the three EM field components Hns, Hew and Er typical of SP+CG flashes The number of columns is positively correlated with the CMC (unlike Adachi et al., 2004)

Optical observations of transient luminous events associated with winter thunderstorms near the coast of Israel Yoav Yair, Colin Price, Michal Ganot, Eran Greenberg, Roy Yaniv, Baruch Ziv, Yosef Sherez, Adam Devir, Jo'zsef Bór, Gabriella Sátori 10observations: 66TLEs 56sprites 6Column (s) 29Column (g) 6Carrot (s) 11Carrot (g) 4Undefined sprite 9elves 7halos 1Undefined: halo/elve All the ELF signals were produced solely by positive cloud-to-ground flashes (+CGs), recorded in Israel (88%) and Hungary (77%). CMC average values of 1400±600 C·km, with some extreme events exceeding 3500 C·km Accepted: Atmos. Res. 2008, special issue ICAE 2007, Beijing

VLF stations: HWU (18.3 kHz; Le Blanc, France; 46.62°N, 01.08°E) NAA (24.0 kHz; Cutler, Maine, US; 44.63°N, 67.28°W). Crete (CR), Greece (35.31°N, 25.08°E) Sde Boker (SB), Israel (30.86°N, 34.78°E) Trying to identify the signature of 15 sprite-producing lightning discharges in the ELF and VLF bands observed during the 2005 Eurosprite campaign.

Main Findings An ELF transient was not associated with sprite occurrence for 5 out of 15 events, suggesting that long continuing current of tens of msec may not always necessary for sprite production For 6 out of 15 imaged sprites there was more than one parent +CG, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space (a few tens of msec and a few km respectively). Column and carrot sprites cannot be identified by either their ELF or VLF signature alone, at least not at the distance to the source of several thousand km as preformed in the present study.

The winter campaign During the winter of sprite campaign in Israel, observations were conducted simultaneously from Jerusalem and Tel-Aviv / Mitzpe Ramon

20:25: Multiple downward leaders

Winter Statistics Type of TLETel-Aviv / Mitzpe-Ramon Jerusalem Columns3618 Carrots68 Mixed / Unidentified 88 Elves6 0 Upward12 Total successful observation nights from Jerusalem: long range detection, weaker storms, low flash rate, few events 4 successful nights from Tel-Aviv: severe light pollution 1 successful night from MR (half of the data!)

Indication for a circular 3D arrangement of sprite columns The appearance of the Sprite element in 3D varies with observation angle, leading to distortion of the circle from ellipse to straight line. We always see a projection in 2D. The ratio of the small and large axis of the ellipse relates to sin δ, which is the angle from the observer’s horizon to the center

Stereoscopic measurements of sprites A simultaneous image of a column cluster from Jerusalem and Tel Aviv taken on December 5 th Severe light pollution precludes stereoscopic analysis. Hypothesis: a combination of an EMP preceding the QE field of +CG. The EMP has a minimum directly above the lightning but increases as a function of r. The QE field has a maximum close to that axis and decreases with r 2. At some critical R the combined effect is sufficient for conventional breakdown.

An Electrostatic Approach An Electrostatic Approach A point charge above a conducting infinite plane simulates the electric field generated above a thunderstorm after the removal of positive charge from the cloud to the ground by an intense lightning discharge. The model is based on a solution for a 3D electrostatic image charge problem (Hiraki and Fukunishi, 2006): Q - total charge [Coulomb] Zs – the height of the charge above the ground [km] For each Qds configuration, we get a critical radius [km] at a specified altitude that matches the breakdown field [V/m] for that altitude.

Convergence and curvature of sprite tendrils The upper part of the brightest bended carrot is tilted diagonally and oppositely with respect to the lower part The 4 Column sprites on the left-hand side also show some bending Cloud luminosity maximum indicates the location of the parent flash is offset with respect to the vertical carrot. Continuing the tendril direction leads to the location of the charge center. The strength of bending might be related to the speed of development and/or delay from the parent CG (Y. Takahashi, P. Communication).

Calibrated spectral measurements of TLEs with the Watec 902H camera Left Sprite: 269 KR* Right Sprite: 301 KR* Talk will be given by R. Yaniv on Friday afternoon during the COST session

First Observation of Blue Jets (?) / Starters – from Jerusalem to a thunderstorm in Jordan. Range ~ 150 km Cloud top was at 11km, the length of the blue jet ~1 km. Total duration was 0.15 s Clear dry air, little dust – excellent viewing conditions towards east. Parent Flash starts at 28/4/ :12:02.384

Summary and future work The MEIDEX kick-started sprite research in Israel and led to many fruitful international collaborations. ELF and VLF data are continuously collected and enable location of parent CGs for sprites anywhere (best for Europe and Africa) Future Plans: calibrated multi-spectral measurements, Additional new instruments and observation points, fully automated sprite tracking system (FAST).

Just outside the footprint of ISUAL.. Optical capacity building in our continued winter campaigns allows coverage of the entire region and offers extensive ground-truth for present and future space- based platforms (SpriteSat, Taranis, ASIM…)

Acknowledgements This research was supported by the Israel Science Foundation grant 145/03 and by the Research Authority of the Open University Thanks to EU COST Action P-18 Physics of Lightning, for enabling young scientists exchange with U. of Toulouse – M. Ganot and O. Van-der Velde Thanks for your attention!

ILAN is a continuation of the MEIDEX conducted by the first Israeli astronaut Ilan Ramon on the space shuttle Columbia in STS-107, January 2003