Radio emissions from RHESSI TGFs A. Mezentsev 1, N. Østgaard 1, T. Gjesteland 1, K. Albrechtsen 1, M.Marisaldi 1, 2, D. Smith 3 and S. Cummer 4 (1) Birkeland Centre for Space Science, University of Bergen, Norway; (2) INAF-IASF, National Institute for Astrophysics, Bologna, Italy; (3) Santa Cruz Institute for Particle Physics, University of California, USA; (4) Duke University, Durham, USA A detailed analysis of RHESSI TGFs is performed in association with WWLLN sources and VLF sferics recorded at Duke University. RHESSI clock systematic offsets are evaluated and found to experience changes on the 5 August 2005 and 21 October 2013, based on the analysis of TGF-WWLLN matches. The clock offsets were found for the whole period of observations with standard deviations less than 100 µ s. In the case of multiple peak TGFs WWLLN detections are observed to be simultaneous with the last peak of the TGF. VLF radio recordings from Duke University also attribute sferics to the second peak of double TGFs, exhibiting no detectable radio emission during the first TGF peak. Spectral characteristics of 81 VLF sferics recorded at Duke University and related to the RHEESI TGFs show that maximal power is emitted between 6 and 12 kHz, which implies the characteristic current pulse width of ∼ 15 to 30 µs. This suggests that the observed TGFs might have substructures including brief intense bursts that are responsible for the radio emissions TGF-WWLLN matching allows to determine RHESSI systematic clock offsets. Time differences between TGF peak times and WWLLN detections being plotted against occurrence date demonstrate three clearly distinct observation periods with different clock offset values. For RHESSI TGFs of 2004, 2005, 2006 and 2011 simultaneous with WWLLN detections there are 17 events that have also simultaneous VLF radio recordings performed at Duke University. Also there were recorded several hundred VLF and ULF sferics within several ms time window around other RHESSI TGFs. Additionally there were selected another 64 TGFs with possible simultaneous VLF sferics. Assuming that TGFs and VLF sferics have the same source locations, the following restricting criteria were used for selection: source location should be consistent with the simultaneity of the TGF and VLF sferic within ±200 µs uncertainty; source location should lay within the azimuthal ±4º cone defined by the ratio of the radial and azimuthal magnetic field components of the VLF sferic; source location should lay in 800 km circle around RHESSI foot-point; source location should lay within a cluster of a current lightning activity validated by WWLLN (or any other lightning detection network). Abstract Double RHESSI TGFs VLF sferics associated with RHESSI TGFs TGF-WWLLN matches RHESSI clock offsets Another two operational space missions capable of TGF recordings, Fermi GBM and AGILE, demonstrate very similar resultant distributions for TGF-WWLLN matches. Standard deviations are remarkably close for all three distributions. This allows to assume that the main contribution into the uncertainty of the TGF-WWLLN matches is given by the WWLLN uncertainty and by the natural variability of the process itself. The search procedure found 357 TGFs (out of the total amount of 2779 TGFs revealed by the off-line search algorithm during the observation period from June 2002 to May 2015) simultaneous with WWLLN sources within ±400 µs, with 320 TGF-WWLLN matches within ±200 µs. TGF peak times were corrected for the propagation time from the WWLLN sources to the RHESSI satellite, the altitude of the sources was assumed to be 15 km in all cases. WWLLN sources within 800 km distance from the RHESSI foot-point were taken into consideration. The wider distribution and a shift of ~0.5 ms compare to the longest observation period was a result of a truncation to a millisecond by the reference time stamping procedure during the initial observation period. After 5 August 2005 this problem was fixed by the RHESSI ground team. Another changes were implemented on 21 October 2013 which led to an additional systematic delay of ~200 µs. Within the analysis period (June 2002 to May 2015) there were found 16 multiple (15 double and 1 multi) peak TGFs with simultaneous WWLLN detections. For 2 of those 16 events we also have VLF and ULF radio waveforms recorded at Duke University, which allows to analyze the time evolution of the radio emissions in addition to the WWLLN data. In all 16 cases the WWLLN detection is simultaneous with the last peak of the multi-peak TGFs. Radio recordings also show a sferic simultaneous with the last TGF peak and no detectable emissions associated with the first TGF peak. Discovered asymmetry in radio signatures associations with multiple TGF peaks might relate to certain peculiarities of the TGF-generated VLF radio emission. Quantitative estimations show that the source fluence of the TGF-producing relativistic electrons gives enough secondary low energy electrons to generate a current pulse which emits VLF sferic. Though, it is hard to distinguish between the VLF pulses related to the +IC leader recoil currents and radio sferic produced by the TGF itself. Growing +IC leader concentrates huge potential drop and electric field in front of its tip, providing necessary conditions for generating TGF. The most favorable conditions for TGF production occur before the attachment. VLF sferic emitted by the recoil current after the attachment is expected to be more powerful compare to pulses emitted during stepping. current in the +IC leader channel after the attachment. the last TGF peak of a multi-peak TGF. A multi-peak TGF can be generated during the +IC leader progression, with most favorable conditions for the last TGF peak to occur before the attachment. After the attachment the most powerful VLF sferic is emitted by the recoil current wave running through the established leader channel. Described scenario gives prevalence for the most powerful VLF sferic (which is more likely to be detected by WWLLN) to be simultaneous (within ±200 µs) to All selected sferics also exhibit a significant ELF pulse which lasts from 2 to 7 ms. This ELF pulse likely refers to the slow current pulse along the +IC leader channel, analogous to a continuing current in CG discharges. This, in turn, makes the VLF sferic more likely to be produced by a recoil to