Extended Abstract (1.5M)2.7
A review of electrical and turbulence effects of convective storms on the overlying stratosphere and mesosphere
Walter A. Lyons, FMA Research, Inc., Fort Collins, CO; and R. A. Armstrong
One still finds statements in meteorological textbooks describing the stratosphere (and higher atmospheric layers) as regions devoid of “weather,” essentially insulated from the chaotic processes of the troposphere. This paper reviews a decade of developments which reveal the stratosphere and mesosphere to be significantly affected by thunderstorms, causing both electrical and dynamical disturbances. Certain classes of thunderstorms can produce cloud-to-ground lightning strokes characterized by charge moments many times larger than described in most text books. Such discharges induce transient electrostatic fields which initiate breakdown processes in the middle atmosphere that trigger the most common of what are now termed transient luminous emissions (TLEs). Called sprites, these vast networks of electrical streamers originate in the mesosphere (around 70 km) propagating vertically upward to ~90 km and downward towards the cloud tops. There is evidence that these events also include “runaway” high energy electrons which couple to the magnetic field, affecting space environments. The volumes of sprites can envelop tens of thousands of cubic kilometers per event. At least 3000 sprites per day are thought to occur worldwide.
Blue jets and giant upward electrical jets have been documented erupting from convective towers. The latter appear to provide direct electrical connections between the tropospheric charge source and the ionosphere, indicating that they may be an important component of the global electric circuit. The energetics of these TLEs are still poorly understood. Early studies suggest they may induce atmospheric chemical processes not included in current atmospheric models. Also, unusual upward lightning-like discharges, sometimes extending thousands of meters above storm tops, have been confirmed. Lasting for as long as 1 to 2 seconds, they are clearly distinct from conventional tropospheric lightning. The implications for aircraft safety and operations are unknown. The initial consideration of a sprite or blue jet as a potential factor the Space Shuttle Columbia disaster (later discarded) emphasized the lack of detailed knowledge of these processes in the middle atmosphere.
In addition to TLEs, thunderstorms are known to generate upward propagating gravity waves which amplify with height, often detectable as luminous periodic perturbations of the airglow layer around 85 km. But at lower altitudes, storm-scale numerical modeling and some limited in-situ observations indicate that turbulent breaking gravity waves and vertical motions (>several m/sec) occur in the stratosphere for thousands of meters above some storm systems. These could significantly affect operations of high altitude airships (HAAs) and unmanned aerial vehicles (UAVs) currently under consideration. Those planning the deployment of platforms in the stratosphere can no longer consider this region (as well as the mesosphere) as dynamically and electrically quiescent. The implications for the next generation of high altitude civil and military aircraft, surveillance systems, HAAs/UAVs, global chemical modeling and the global electrical circuit will be discussed.
Supplementary URL: http://www.FMA-Research.com
Session 2, Connections with Meteorology, Data Assimilation and User Needs (Room 617)
Tuesday, 13 January 2004, 1:45 PM-5:30 PM, Room 617
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