Recent Developments in Atmospheric Electricity (Publication to Commemorate the 90th Birthday of Stanisław Michnowski)
The present publication contains the contributions presented during the Jubilee Session organized to commemorate the ninetieth birthday of Stanisław Michnowski, many-year leader of the atmospheric electricity group at the Institute of Geophysics, the pioneer of atmospheric electricity and thunderstorm research in Poland, and world-renown expert in this field. The Jubilee Session was held in Warsaw on November 20, 2008.
Series: (D-73), 2009, pp.3-3
Series: (D-73), 2009, pp.5-6
Recollections, congratulations and wishes on the occasion of Stanisław Michnowski’s jubilee
Series: (D-73), 2009, pp.7-8
Eighty years of fair-weather atmospheric electricity monitoring in Poland
Series: (D-73), 2009, pp.9-14
The aim of this note is to draw greater attention to the fact that the Institute of Geophysics is in possession of atmospheric electricity measurement results from Świder for about 80-year period. The data are reliable and of good quality owing to the efforts of Stanisław Warzecha, head of the Świder Geophysical Observatory, and Stanisław Michnowski, head of the atmospheric electricity group at the Institute. With a view to the global climate changes, such materials may provide valuable background for various studies.
Brief outline of the long history of collaboration between the Central Laboratory for Radiological Protection and the Atmospheric Electricity Laboratory of the Institute of Geophysics
Series: (D-73), 2009, pp.15-21
The response of towers and other structures to nearby lightning
Series: (D-73), 2009, pp.23-35
This study describes an attempt to evaluate the potentially hazardous effects on tall structures from nearby cloud-to-ground flashes by conducting measurements of currents and ground potentials on structures during thunderstorms. The analysis of these measurements has shown that the layout of the elements of ground structures and their connections within a grounding grid of the installation have profound effects on magnitudes and polarities of induced currents and voltages. Understanding of the factors affecting the response of tall ground structures to nearby lightning flashes, and therefore correct interpretation of induced lightning effects on a particular installation is crucial for improving the design of grounding systems of the installations.
Modelling the Earth’s Global Atmospheric Electric Circuit - development, challenges and directions
Series: (D-73), 2009, pp.37-53
In this paper we summarise modelling work to date concerning the Earth’s global atmospheric electric circuit. We discuss the development of the models over last decades and some features that require improvements in future models. We consider various atmospheric and ionospheric data sets and models available which can support and improve the current and future modelling of the global electric circuit. We also highlight the new high-resolution model of the global atmospheric electric circuit, EGATEC, currently developed at the University of Leicester.
Variations of the mid-latitude atmospheric electric field (Ez) associated with geomagnetic disturbances and forbush decreases of cosmic rays
Series: (D-73), 2009, pp.55-64
Observations of the atmospheric vertical electric field component (Ez) at the mid-latitude Polish station Świder have been analyzed during 14 strong and moderate magnetic storms. Only data recorded under the so-called “fair weather” periods have been used for this analysis. The daily Ez variations under quiet geomagnetic conditions were established. The seasonal Ez level variations have demonstrated the winter maximum and summer minimum. The effect of the main phase of magnetic storm was discovered in the daytime mid-latitude Ez variations during any local magnetic activity. Short-time strong negative Ez excursion relative to the magnetically quiet daily level has been observed in the daytime simultaneously with magnetosphere substorm onset at the night sector. The long-duration depletion of the Ez amplitudes was found in association with Forbush decreases of galactic cosmic rays.
The results obtained can be interpreted as a significant influence of the changes in the solar wind-magnetosphere-ionosphere system on the global electric circuit state.
Preliminary analysis of dynamic evolution and lightning activity associated with supercell event: case story of the severe storm with tornado and two heavy hail gushes in Poland on 20 July 2007
Series: (D-73), 2009, pp.65-88
A violent explosion of deep convection struck many countries in Europe on 20 July 2007. In that day, severe thunderstorms were accompanied by floods and harmful winds, and even by one 8-minute incident of tornado in Poland. In this paper we have presented the detail analysis of supercell dynamic development connected with tornado incident and the time and space behavior of its lightning activity detected by the SAFIR/PERUN network system. For this purpose, we have used reflectivity data from four Doppler radars, i.e., in Ramża, Pastewnik, Brzuchania and Legionowo, to obtain as realistic as possible history of the 3- dimensional dynamic evolution of convective complex which started to develop over south Poland. We were able to distinguish 5 stages of such a convective evolution, i.e., for the time interval 00 04 UT – the nocturnal dissipation of previous convective structures; between 04 and 10 UT – the further development and dissipation of few new convective cells; between 10 and 14 UT – the development of one large convective cluster and a new convective single cell – a precursor of the next aggregation and supercell; between 14 and 16 UT – the further growth/enlargement of the supercell; and finally between 16 and 18 UT the mature stage of supercell with tornado near Częstochowa associated with a growth of a new convective complex developing over the Tatra mountains and Slovakia. To perform relevant interpretation of the composite radar pictures we prepared, we used two computer simulations with different grid resolutions; the first one concerned the region over Europe, with 14 km grid step and divided into 35 levels, and the other one, nested over Poland (the COSMOLM model, see Steppeler et al. 2003), with grid step squeezed up to 2.8 km and vertical resolu- 66 tion of 50 levels. Moreover, we have taken into account two additional important sources of data: the cloud coverage from satellite observations and the accompanying lightning activity from the SAFIR/PERUN detection system. The numerical forecast model applied predicted many characteristic singularities of the observed real weather situation and gave us also a possibility to get a much deeper insight into some fine mechanisms which could be considered as steering for the studied case, e.g., the occurrence of right- and left-mover wind patterns during convective development of the tornado system. We have also included to our analysis the examination of the observed lightning rate changes of particular convective complexes before and after the supercell aggregation. On the other hand, locations of positive and negative return strokes of cloud-to-ground flashes (RS+ and RS ), and intra cloud discharges (IC) given by the SAFIR/PERUN system in the supercell area revealed their specific clustering co-located with precipitation/hail shafts and previous widespread IC lightning activity followed by grouped CG± flash strokes.
Dynamics of lightning channel corona sheath predicted by return-stroke models with specified longitudinal current distribution
Series: (D-73), 2009, pp.89-98
We consider dynamics of the lightning-channel corona sheath that is implicitly specified by lumped-current-source (LCS) type (transmission-line-type) and distributed-current-source (DCS) type (traveling-currents-source type) lightning return-stroke models. A relaxation model of charge motion in the corona sheath is used to investigate the rate of its expansion and shrinking. This model can be viewed as a generalization of the model proposed by Maslowski and Rakov (2006) and can be applied to both LCS and DCS return-stroke models with specified longitudinal current distribution.
Natural lightning channel evolution obtained from high-speed digital video camera recordings
Series: (D-73), 2009, pp.99-107
First Polish recordings of natural lightning channel evolution obtained from high-speed digital video camera Phantom MIRO 4 on millisecond-scale resolution are presented. The camera was mounted at the observation point on the seventh floor of a high building in Warsaw during thunderstorm condition on August 15, 2008. Three series of digital recordings of CG flashes with relatively good quality were collected, that is, (1) the fork lightning with two terminations to ground, (2) the lightning flash discharge including continuing current, and (3) the CG flash together with some preceding in-cloud discharges activities. The obtained recordings show that high-speed digital video camera with the time resolution of 1 ms and large own buffer memory (4 GB) can be used to keep track/trace of the entire lightning discharge time evolution. However, in order to investigate in greater detail the process of initial stage of return stroke, notably when its current front is traveling between ground and cloud, it would be desirable to have the camera recording possibility giving the time resolution less than ten microseconds. The optimum way of recordings of natural lightning channel time evolution requires at least two digital cameras working simultaneously with very good GPS time synchronization and having different time resolution and other optical parameter settings. This can prevent undesirable overexposures caused by very large luminosity changes/bursts associated with rapid lightning current flow during the return stroke stages. Another advantage of simultaneous using of two digital cameras viewing at different azimuth angle toward the same and possible lightning flash hitting, e.g., in a very high object, is a chance of obtaining/reconstructly the real three dimensional picture of all visible lightning branches together with its main channel for such flash event. We plan to do that experiment during our next field measuring campaign, using two separated high speed cameras, having very good time synchronization supplied by the external IRIG-B connection.
Engineering utilization of the results of lightning research
Series: (D-73), 2009, pp.109-120
This paper deals with the way in which the data on lightning discharges are utilized by engineers for lightning protection. A comprehensive review of these data and their selected features, important from lightning hazard point of view, is followed by a description of the hazard assessment methods. The role of Stanisław Michnowski in lightning discharge physics is pointed out.
Preliminary assessment of ions distribution in the atmospheric mixed layer based on a single column model
Series: (D-73), 2009, pp.121-128
The distribution of ions in the convective boundary layer (CBL) is investigated based on a non-local closure model. The obtained results show that the ion fluxes are not linear and exhibit distinct maxima. The fluxes of small ions, large ions, and aerosol particles strongly differ from each other. Vertical profiles of small ion concentrations are less variable with height than those of large ions. The lifetime of ions versus the eddy turnover time of the CBL is of decisive influence for shaping their fluxes and vertical profiles. The resulting vertical profiles of ions are used for estimating the electrical convective current.
Ground-level electric field and current variations in polar and mid-latitude regions, in relation to solar wind changes (extended abstract)
Series: (D-73), 2009, pp.129-131
Researches on a relationship between the lower atmosphere electricity and solar wind (SW) changes are still meager and delayed in comparison to impressive advances in investigations of the magnetosphere and ionosphere (M-I) dependence on these changes. Remarkable increase of the knowledge on the SW−M-I coupling seems to open new possibilities for a more effective study of the SW effects on the vertical component of electric field (Ez) and electric current (Jz) monitored near the Earth surface. These effects are still not much known and understood in spite of their potential utility in studies of physical processes involved in weather and climate changes in the lower atmosphere. Although some correlations between the SW−M-I and the corresponding atmospheric electricity parameters have been established, on the basis of station observations in the Antarctida, as statistically significant, the number of data on direct physical dependences between them in individual cases is still very scarce. The shortage of systematic atmospheric electricity observations is particularly drastic in the Arctic, despite the fact that at high latitude regions of Northern Hemisphere the modern M-I investigation facilities have been implemented and are in service for a long time.
This paper presents the results of investigation of ground-based electric field, Ez, and current, Jz, response to solar wind changes in the Arctic and in middle latitudes on the basis of the recordings at Hornsund (Spitsbergen) and atmospheric electricity observations at Świder (Poland). Individual events were demonstrated in considerable number for selected coincidences with various M-I states and configurations that were actually imposed by solar wind. Also, cases of average and individual daily Ez and Jz variations for fair-weather in coincidence with quiet magnetic conditions were used, mainly for comparison. The electric ground-level recordings were presented on the background of data on corresponding concurrent solar wind and M-I changes obtained by internet from satellite missions, the magnetic station networks, coherent polar radars, riometer nets and other sources. This approach allowed to discern and show some features of the possible polar and middle latitude Ez and Jz responses to characteristic SW−M-I changes. (Few fragments from subtropical Vietnamese-Polish atmospheric electricity recordings at Sa-Pa in Vietnam are supplementarily used, although they were with limited background of geophysical conditions. It is to be noted that long-term continuous recordings at Sa-Pa and Phu-Lien are waiting to be accessible from Vietnamese Institute of Oceanology in Hanoi, Vietnam).
Various repeatedly occurring solar wind effects on Ez and Jz variations were revealed by their comparison with corresponding ones in undisturbed, fair-weather and magnetically quiet conditions. The Ez variation events were preceded by changes mainly in solar wind, interplanetary magnetic field intensity and in its orientation, in solar wind pressure, solar wind electric field intensity and its orientation, and in solar wind velocity and density. The recorded effects extend previous observations largely, not only in number and diversity of their signatures, but first of all in pointing out their relations to solar wind and corresponding M-I configuration changes. In some examined cases, the solar wind changes might be compared in an extent with the changes in ionosphere potential distribution estimated by the known empirical models, and by conductivity changes in and below the ionosphere, produced by energetic particle precipitation, partly shown by the riometer indications. All these factors affect the Ez values. In the polar region, most of the presented Ez effects were found for the first time during the main and recovery phases of geomagnetic substorms, during sudden enhancement of geomagnetic storms, and even at quiet magnetic conditions. The first-time detected occurrences at mid latitudes of the impressive individual Ez responses to the main phase of magnetic storms are especially remarkable. Their striking large amplitudes, sometimes comparable to the total ground-level values in the global electric circuit, and quite long duration, up to one or two hours, have to be taken into account in extension of present models of the global electric current circuit (GECC) in the lower atmosphere.
The findings gathered in this study show that the ground-level electric measurements are able to bring very interesting data on the lower atmosphere dependence on solar wind changes, most often via magnetosphere-ionosphere effects. On the other hand, they allow to increase significantly our knowledge on global electric current circuit in the lower atmosphere. Since the GECC in the lower atmosphere and the solar wind imposed magnetosphere current circuits are closed by common ionosphere medium, a joint treatment of them is justified, at least in the studies of electrical coupl- 131 ings of the lower atmosphere with the SW−M-I system. A suggestion of preliminary, very simplified but common model of the global electric current circuit in lower atmosphere and the general model of electric current circuit in the near geospace was put forward.
Bibliography of Stanisław Michnowski’s publications in chronological order (1955-2009)
Series: (D-73), 2009, pp.133-142