Characteristics of narrow bipolar pulses observed in Malaysia

Narrow bipolar pulses (NBPs) are considered as isolated intracloud events with higher peak amplitude and strong high frequency emission compared to the first return strokes and other intracloud discharges. From 182 NBPs recorded in Malaysia in the tropic, 75 were narrow negative bipolar pulses (NNBPs) while 107 were narrow positive bipolar pulses (NPBPs). The mean duration of NNBPs was 24.6±17.1 μs, while 30.2±12.3 μs was observed for NPBPs. The mean full-width at half-maximum (FWHM) was 2.2±0.7 and 2.4±1.4 μs for NNBPs and NPBPs, respectively. The mean peak amplitude of NPBPs normalized to 100 km was 22.7 V/m, a factor of 1.3 higher than that of NNBPs which is 17.6 V/m. In contrast to the previous studies, it was observed that the electric field change was characterized by a bipolar pulse with a significant amount of fine structures separated by a few tens of nanoseconds intervals, embedded on it.     

Solar forcing on antarctic terrestrial climate: A study by means of GPS observations

With a view to difficulties with explaining the physical mechanism of solar forcing on the Earth’s climate, we applied a new approach of determining and quantifying an influence of solar-related events on water vapor variability by correlating the total electron content (TEC) and precipitable water vapor (PWV), both derived from ground-based GPS observations. In this study, ionospheric TEC and atmospheric PWV values are employed as solar activity and terrestrial climate parameters, respectively. Three-year GPS data at five stations in Antarctica are analyzed on a daily mean basis. Results show significant correlation between TEC and PWV differences during storms-affected days. The high correlation between the daily mean values of TEC and PWV, both of which follow the seasonal signals and subsisting downward trend, suggests an influence of solar activity on climate variability in Antarctica. These quantities are determined by changes of the upper-atmosphere level, which varies in conformity with the zenith angle of the Sun.     

Observations of Antarctic precipitable water vapor and its response to the solar activity based on GPS sensing

Predicting global climate change is a great challenge and must be based on a thorough understanding of how the climate system components behave. Precipitable water vapor (PWV) is one of the key components in determining and predicting the global climate system. It is well known that the local surface temperature and pressure have a direct influence on the production of PWV. However, the influence of solar activity on atmospheric dynamics and their physical mechanisms is still an open debate, where past studies are focused at mid-latitude regions. A new method of determining and quantifying the solar influence on PWV based on GPS observations to correlate the GPS PWV and total electron content (TEC) variations is proposed. Observed data from Scott Base (SBA) and McMurdo (MCM) stations from 2003 to 2005 have been used to study the response of PWV to solar activity. In the analysis, the effects of local conditions (wind speed and relative humidity) on the distribution of PWV are investigated. Results show significant correlation between PWV and solar activity for four geomagnetic storms, with correlation coefficients of 0.74, 0.77, 0.64 and 0.69, which are all significant at the 95% confidence level. There was no significant correlation between TEC and PWV changes during the absence of storms. On a monthly analysis, a strong relationship exists between PWV and TEC during storm-affected days, with correlation coefficients of 0.83 and 0.89 (99% confidence level) for SBA and MCM respectively. These indicate a statistically significant seasonal signal in the Antarctic region, which is very active (higher) during the summer and inactive (lower) for the winter periods.     

GPS observations at quasi-conjugate points under disturbed conditions

The conjugacy effects of the GPS scintillation activities during the geomagnetic storms of October 2003, November 2003 and July 2004 have been investigated at the approximately geomagnetically conjugate stations: Scott Base, Antarctica (SBA) and Resolute Cornwallis Island (RESO) in the high Arctic region. The measurements aim at investigation of the similarities and differences of the scintillation activities occurring at the conjugate points in the polar regions under storm conditions and examine the relationship between the Storm Enhanced Density (SED) and scintillation activity. The measurements of the scintillation activities obtained from total scintillation index during these storm periods at both hemispheres showed asymmetry in the ionospheric scintillation occurrence at the conjugate points. Pronounced scintillation activity was observed at the nightside hemisphere with the total scintillation index higher than at the dayside hemisphere. The results also show that the durations of severe scintillation activity were longer at the nightside hemisphere. The measurements showed that the intense scintillation periods were corresponding to the presence of the SED events where more pronounced SED events were observed over the nightside hemisphere.     

The response of TEC at quasi-conjugate point GPS stations during solar flares

Global Positioning System (GPS) derived total electron content (TEC) measurements were analyzed to investigate the ionospheric response during the X-class solar flare event that occurred on 5-6 December 2006 at geomagnetic conjugate stations: Syowa, Antarctica (SYOG) (GC: 69.00°S, 39.58°E; CGM: 66.08°S, 71.65°E) and árholt, Iceland (ARHO) (GC: 66.19°N, 342.89°E; CGM: 66.37°N, 71.48°E). Bernese GPS software was used to derive the TEC maps for both stations. The focus of this study is to determine the symmetry or asymmetry of TEC values which is an important parameter in the ionosphere at conjugate stations during these solar flare events. The results showed that during the first flares on 5 December, effects were more pronounced at SYOG than at ARHO. However, on 6 December, the TEC at ARHO showed a sudden spike during the flare with a different TEC variation at SYOG.     

The first electric field pulse of cloud and cloud-to-ground lightning discharges

In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as ‘small’, ‘medium’ and ‘large’, depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.