סמינר בחוג לגיאופיזיקה: Ground and airborne measurements of electrical parameters above Israel

Abstract:

The global electric circuit (GEC) on earth is driven by electrified shower clouds and thunderstorms that act as current generators. The current flows up to the ionosphere and returns back to earth in areas known as fair weather regions. One of the GEC parameters that is routinely measured is the vertical electrical field (Ez) with a typical fair weather value between 100-300 V/m near ground. The Ez was found to correlate with the diurnal global thunderstorm activity in what is known as the Carnegie curve (Rycroft et al., 2012).

Ground based stations that measure the daily mean variations of the Ez during fair weather are currently operational and located in the arid region of Mitzpe Ramon, Negev desert in southern Israel (30.6N, 34.76E, altitude 860 a.s.l) (Yaniv et al 2016a) and at the Tel-Aviv University Cosmic Ray Observatory on Mount Hermon, in northern Israel (33.3N 35.78E, 2100 a.s.l). We present results of the mean daily variations of Ez recorded in these stations, showing a strong mid-day effect in the mountainous stations (Hermon) and a local morning effect of aerosols in the arid station that is absent from the famous oceanic Carnegie curve. This strong mid-day local effect in mountainous regions were previously observed by several authors and referred to as “Austausch” – The rising of a charged aerosol layer due to solar morning heating of the ground. The transport of electrical charge results in an increase of the local Ez (Chalmers 1965, Cobb et al 1967, Israël 1970).

Airborne balloon measurements up to 35 km above Israel show Ionization variability in the upper atmopshere with a maximum around 17-20 km called the Regner-Pfozer max that agree well with other observations from around the world. The Israeli results shows latitude dependence to other measurements and agree with model results (Yaniv et al 2016b). Radiation dose rate calculations at the altitude of commercial flights (~10km) were found to pose no risk to human health. Ionization and Radiation dose rates were found to increase as we proceed from solar maximum to solar minimum. (Yaniv et al 2017 under review).

מארגן הסמינר: פרופ' איל חפץ