Initial Results from PhOCAL 2012 Field Operations

The multi-year, multi-institution effort entitled Physical Origins of Coupling to the Upper Atmosphere from Lightning (PhOCAL), has among its goals, to qualitatively understand the meteorology and lightning flash characteristics that produce the unusual and/or very energetic lightning responsible for phenomena such as sprites, halos, elves, blue jets and gigantic jets, collectively known as Transient Luminous Events (TLEs). A key task is to obtain simultaneous video, ideally with a high-speed imager (HSI), of both a TLE and its parent lightning discharge, within the domain of a 3-D Lightning Mapping Array (LMA). While conceptually simple, this task is logistically very complicated. A primary tool to locate likely sprite parent +CGs (SP+CGs) is the Charge Moment Change Network (CMCN), which provides (near) real-time maps of high impulse charge moment change (iCMC) events (using geolocation from the NLDN). Those uncommon +CGs with iCMCs values >100 C km have a likelihood of inducing sprites of > ~10%, with values approaching ~75% for values > 300 C km. Using the CMCN, a number of automated low-light Watec cameras comprising a SpriteNet system can be oriented to monitor the atmosphere above convective storms occurring within LMAs in Colorado, New Mexico, Texas, Oklahoma, Alabama and the DC area. Triangulations from multi-camera detections have been achieved. Several SP+CGs originating in the anvils of supercellular storms were recorded, a departure from the most favorable meteorological regime (a large MCS). These storms also generated trains of middle atmosphere gravity waves imaged with a broad spectrum DSLR camera. An Intensive Observation Period (IOP) was conducted, with a fixed-based intensified HSI (Lubbock, TX) teamed with a mobile van deployed to capture the SP+CG within an LMA. The drought conditions that plagued the 2012 IOP, while less severe than the preceding year, limited the number of nocturnal MCSs. Several “near miss” intercepts proved that the “chase scenario” is feasible. One mission also imaged a +CG, which was followed by Lightning Triggered Upward Lightning (LTUL) event from a tall tower, a scenario that appears to occur frequently in sprite producing MCSs. A dramatic elve plus halo was imaged at 3000 ips, associated with a 243 kA +CG. The newly commissioned Colorado LMA was traversed by two intense, sprite-producing MCSs in June. In one, coincident HSI videos of several distant SP+CGs with recoil leaders and long continuing currents were obtained. HSI captures of a nearby +CG also exhibited recoil leaders. A newly instrumented Lightning Intercept Vehicle (LIV) was commissioned in August to greatly increase the efficiency of mobile video monitoring of SP+CGs within LMAs.