Walsh Medical Media

Heading : International Storm/Tornado Results

Tornadic activity is ‘popping up’ with increasing frequency in other parts of the world, for example, as recently reported in detailed studies of such activity in South America, Europe and Asia [<a href="#21" title="21">21</a>-<a href="#23" title="23">23</a>]. Argentina has its own tornado alley in the La Pampa region where occurrences were compiled from newspaper accounts [<a href="#21" title="21">21</a>]. In the study, satellite and radar measurements were employed to monitor hail and, especially, lightning frequency as a proxy for intense and developing storms, reaching a not very high ~0.3 s-1 flash rate in the mountainous region of the Argentina/Chile border, with reported tornadoes occurring further east in the central Pampas. Higher accounts of such flash rates in the US, both experimentally observed and employed in model calculations, are to be discussed. For a particular tornadic storm in Catalonia, at the Spanish east coast of the Iberian Peninsula extending into the Mediterranean Sea, detailed satellite and radar measurements of both CG and IC flash rates were analyzed for moderate lightning activity, heavy rainfall and a weak tornado inflicting minor ground damage [<a href="#22" title="22">22</a>]. A maximum IC lightning flash rate reaching ~0.04 s-1 was measured just before tornado appearance and much smaller flash rate -1 for –CG updraft wind. Several features noted were a relatively low CAPE value, high precipitation, low buoyancy but no lightning jumps during the tornado. An initial sharp increase of the IC flash rate was associated with presumption of a stronger wind shear associated with the storm.

Of greater interest to our purpose is the case study presented for a microphysics analysis of a severe thunderstorm in India in which case the storm features were simulated with the Weather Research and Forecasting (WCF) model and compared with experimental observations and other model simulations [<a href="#23" title="23">23</a>]. Investigation of the storm focused on cloud-ice nucleation/generation among mixed phases in relation to CAPE, wind speed, maximum reflectivity, vertical velocity and the microphysics of latent energy release. The cloud ice and mixed phase processes were pointed out to be responsible for electrical activities inside the cloud. The storm intensity was taken to be especially enhanced by an increased updraft produced by greater latent energy effect of heating in the upper troposphere. Model equations were described for prediction of both mixing ratio and number concentrations of cloud hydrometeors spanning the conversion of water vapor into ice and mixed phases of snow and graupel, all within the convective cloud system. The vapor, moisture, ice and graupel content of the convective cloud system was shown to be an extremely important part of the severe storm problem. And this part of the complex interactive system was the subject of special study. In related investigation of the water-ice system, Marciante and Calvo [<a href="#24" title="24">24</a>] have recently asserted that ‘Nucleation of water droplets from a supersaturated vapor is a basic atmospheric process involved in cloud, mist, and aerosol formation. The general understanding of nucleation through the seminal classical nucleation theory relies on equilibrium thermodynamic considerations. In practice, [the theory] contains a significant number of approximations in its evaluation of the critical nucleus, and often fails quantitatively against experiment or detailed numerical simulations if its ingredients are not known accurately enough’. Merciante and Calvo concentrate on the chemical physics of ‘sticking’ cross-sections of water molecules on cold sizeselected water clusters involving classical and quantum (path-integral) molecular dynamics simulations and provide comparison with experimental results. Earlier mention of Benjamin Franklin’s surmised disappointment would no doubt be partly alleviated by such modern accumulation of knowledge that has been gained in the interim years of studying the complexity of microphysics within a severe storm system.

Electrical Role for Severe Storm Tornadogenesis (and Modification)

Heading : International Storm/Tornado Results