Diurnal variation of surface electric field at a tropical station in different seasons: a study of plausible influences

Abstract

Based on the fair weather days of 1993 surface electric field at Pune (18 32 N, 73 51 E, 550 m ASL) is studied for its diurnal and seasonal variations. The analysis attempts to look into factors like atmospheric pollution and space charge formation in presence of the meteorological factors prevalent in the three seasons that modify the global effects that govern fair weather electric field at the site of measurement. Summer (FMAM), monsoon (JJAS) and winter (ONDJ) are the seasons considered. By and large diurnal variation is with double oscillation. The results show high persistent value of electric field during monsoon. Evening peak is the highest during winter with high atmospheric stability conditions and summer afternoons have the lowest value. Space charge formation depending on the wetness or dryness of the ground is proposed in connection with the high and low values of electric field close to ground. It appears that space charge is equally or more important in contributing to electric field variations as conductivity as for local effects. The generation of positive space charge occurrence in connection with evaporation and negative space charge occurrence with very dry ground bypassing the local component to global one due to large area coverage elsewhere as well, under similar weather conditions are suggested. Possibility of monsoon field showing a glimpse of global activities being a cleaner tropical environment during this period is also discussed. Observational verification of space charge formation and the role it could be playing, on abundantly available, by the then active physical processes plays on thunderstorm electrification based on convective theory is mooted.

Characteristics of the atmospheric electric field and correlation with CO2 at a rural site in southern Balkans

“…During the warm months of June to October, the PG exhibited its primary maxima at 10:00-11:00 LT, whereas during the cold months of November to January, the corresponding maxima were transposed to 12:00-14:00 LT. This transposition is attributed to the earlier initiation of convective conditions during the warm months and the subsequent earlier activation of the sunrise effect (Latha 2003) and is in agreement with the results at other continental sites (Retalis and Retalis 1997). The remainder of the months, February to May, showed intermediate behavior, exhibiting their maxima at 11:00-12:00 LT.…”

“…However, both extrema are susceptible to local effects that could enhance or suppress the global signal. The convective conditions maximized earlier that caused a minimum at 18:00 LT were gradually weakened, resulting in increased aerosol concentration close to the ground and subsequently increased PG, as described above (Latha 2003). On the contrary, the gradual transition to nocturnal stratification could cause trapping of radon and its progeny, resulting in intense ionization conditions and the creation of negative space charge (reversed electrode effect), which would eventually suppress PG (Hoppel et al 1986;Latha 2007).…”

“…In that case, the electrode layer that was formed on the mountain's surface during the night is also diluted after sunrise, and after being transported upslope, the positive charges can be advected over the EFM via the returning cell circulation. The significance of the sunrise effect on the morning peak was also emphasized in studies for other stations, irrespective of the character of the site, including typical continental (Retalis and Retalis 1997), tropical continental (Latha 2003), or island tropical (Kumar et al 2009). …”

Diurnal variation of atmospheric Maxwell current over the low-latitude continental station, Tirunelveli, India (8.7°N, 77.8°E)

“…The Maxwell current data from Tirunelveli do in fact reflect the global changes in the atmospheric electrical parameters, and they are not contaminated by local disturbances. The sunrise effect measured at Pune, another tropical Indian site, using a field mill has been reported in a recent publication (Latha et al, 2003). The morning rise is attributed to a local effect, and the same effect is not ob- Fig.…”

Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji

“…Close to the surface, the PG values during fair-weather conditions normally range from 100 V m −1 -200 V m −1 . Surface fair-weather PG measurements have been frequently used to investigate the electrical properties of the atmosphere, be it global, regional or local (Latha, 2003). Long term measurements of PG over the oceans feature a clear global diurnal pattern with a peak around 1900 UT and this trend is known as the Carnegie Curve (Israel, 1973).…”