Walsh Medical Media

Heading : Atmospheric Lightning

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			Physics Today has recently reproduced the classic 1970 description given by Hans Panofsky of the global hydrodynamic and thermodynamic equations governing atmospheric behavior [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#25" title="25">25</a>]. Four basic relations were presented: (1) an equation of state for dry air; (2) an equation for the thermodynamic system, including ‘eddy’ conduction and rate of energy addition by radiation; (3) continuity of material; and (4) Newton’s 2nd law for a rotating body. Inclusion of water vapor as the most important compositional variable was proposed to enter through the first two equations and with need for additional conservation equations. Attention was directed to interaction of the oceans and the atmosphere in influencing surface temperature patterns. Lightning was considered to be at a scale too small for consideration, as has been true until recent years in weather forecasting. Cloud seeding was mentioned as an example for mesoscale application of the equations and in relation to the as yet unknown effect on a hurricane.

A modern introduction to lightning beginning from the time of Benjamin Franklin is given in the recent book by Cooray [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#26" title="26">26</a>]. In relation to the environmental reference made by Panofsky, Williams has produced an important review of lightning activity within the global electrical circuit [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#27" title="27">27</a>]. Included topics were: (1) climate aspects of lightning and rainfall in the general convective circulation; (2) extremes in climate brought on by thunderstorms and lightning; (3) main temperature differential influences relating to cloud buoyancy; and, (4) the microphysics aspects of aerosols on cloud electrification. More extreme cloud systems were indicated to come for a warmer world but there is as yet no indication of enhanced mean thunderstorm lightning flash rates. In another report, Williams focused on further details of the physics of lightning by describing the ‘polarity asymmetry’ characteristics of positively and negatively charged flashes both in CG and IC occurrences, including in the latter case only production of gamma rays directed upward into space [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#28" title="28">28</a>]. The observed asymmetries were taken to be associated with the microscopic asymmetry in mobility to be expected for free electrons and positive ions. Armstrong and Glenn employed such argument for the role of lightning-produced (electrons and) ions in tornadogenesis [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#12" title="12">12</a>]. There is newspaper report of a rare form of ‘dark lightning’ associated with both gamma rays and x-rays being generated by energetic electron collisions with atoms and molecules within storm clouds [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#29" title="29">29</a>].

Evidence of variations in lightning character, both for IC and CG activities, was presented by Marshall and Stolzenburg [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#30" title="30">30</a>] in a one-dimensional model description of changed electrostatic energy within a horizontally stratified cloud producing a ‘spider type’ flash occurrence. Focus was on the constraint provided by amount and (vertical) distribution of the charge structure. A voltage gradient of ~10 to ~120 kV/m was taken to be typical within and below a typical storm cloud, compared to Vonnegut [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#3" title="3">3</a>] employing a relatively low voltage gradient of ~110 kV/m to obtain an order of magnitude estimation of a charge density of ~5 x 103 elementary charges/cm3 being associated with lightning production. So-called sprite production associated with Q-bursts was attributed to a cloud structure having an electrostatic energy of ~1010 J, say, compared to between 5 × 1011 and 2 × 1012 J within a mesoscale convective storm system, allowing a considerable number of (positive) lightning flashes in the range of ~107 to 109 J in addition to the smaller number of energetic +CG flashes generating Q-bursts. The quantitative model calculations reported by Marshall and Stolzenburg were correlated with measurements obtained from balloons carrying electric field meters and meteorological radiosondes. The subject of electric discharges in the mesosphere was surveyed by Neubert, Rycroft, Farges, Blanc et al. with attention given to coordinated storm observations made in Southern Europe and including IC ‘sprite’ activity, ionization, electromagnetic radiation, and ‘runaway’ energetic electron actions [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#31" title="31">31</a>]. Metzger and Nuss [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#32" title="32">32</a>] have pointed more recently to the National Lightning Detection Network using sferics via low and verylow frequency radio bands to detect CG lightning strokes and timeof- arrival analysis with high and very-high frequency radio bands for such IC stroke detections. Several such systems were set up in Florida, Alabama and New Mexico. From such comprehensive measurements, the stroke or lightning flash detections were categorized according to accompanying severe wind or hail or mixed-type associations. A relative increase in CG over IC lightning activity occurred for onset of severe (ground level) wind behavior whereas the IC flash rate increased relatively over CG for hail type association and total lightning activity that always preceded the onset of severe weather. The preceding lightning behavior was taken to relate to the strength of updraft wind action as mentioned in numerous preceding studies.

Low frequency (1 Hz) infrasonic observations coordinated with Doppler radar measurements were reported by Bedard [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#33" title="33">33</a>] in which a vortex whose maximum circulation was detected within an IC storm on 7 June 1995 in eastern Colorado and then was tracked on an eastwardly descending direction for approximately 30 minutes before evolving into a full-fledged tornado on the ground. The infrasonic method, that had been included in the mentioned survey by Neubert et al. [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#31" title="31">31</a>] of electrical discharges in the mesosphere, provides for detection at distances up to ~1000 km, as also described by Bedard, and relates to monitoring of the acoustic energy contained in radial modes of vortex vibrations. Bedard employed results from the method also in several analyses of other archival observations of tornadoes. The infrasonic method is important because of being capable of providing evidence of otherwise unseen tornadogenesis being initiated within the IC structure. In a later report, Fierro et al. [<a href="https://www.walshmedicalmedia.com/admin/index.php?page=omics-ft-fullview&old_omics_id=61637&title=Electrical+Role+for+Severe+Storm+Tornadogenesis+%28and+Modification%29#34" title="34">34</a>] outlined a test case of describing initiation of storm convection at a cloud-resolving scale via incorporation of total lightning data within a numerical weather research and forecasting (WRF) model, also done in conjunction with the Advanced Research WRF dynamic solver. Deep moist precipitating convection of water vapor and graupel was required to occur within the storm cloud structure in order to obtain agreement in the simulation of available measurements of storm parameters. Lightning flash rates from 0-0.7 s-1 were employed in the numerical calculations. The modeling of observations was judged to be promising. Of particular note was the observation that an incremental increase of water vapor at constant temperature in the vicinity of lightning regions led to acceleration of buoyancy and ultimately greater wind updraft in the modeled cloud behavior.
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Electrical Role for Severe Storm Tornadogenesis (and Modification)

Heading : Atmospheric Lightning