查看更多>>摘要：This paper investigated the indirect effects due to sea-salt aerosols on tropical cyclones using the Weather Research and Forecasting model, coupled with a chemistry module (WRF-Chem). The parameterization of seasalt aerosols in the model was operated. The domain-averaged vertically integrated cloud auto-conversion rates were 0.699 and 0.038 mm/h with and without the inclusion of the aerosol indirect effects, respectively. Cloud ice deposition and mixing ratio were higher with inclusion of indirect effects than without. Conversely, the cloud top temperature at a specified time was lower with indirect effects than without. When indirect effects of aerosols were included, the 0.01 g/kg contour line of the azimuthally and temporally averaged cloud ice mixing ratio increased by about 500 m. Overall, the inclusion of the aerosols indirect effects led to the extension of the cloud tops of tropical cyclones to greater heights.
查看更多>>摘要：The effect of Ground Level Enhancements (GLEs) on the atmospheric and dust particles electrical properties is studied. It has been found that in the case of fair weather conditions, GLE events enhance the atmospheric electrical conductivity, reduce the columnar resistance, and modify the fair weather electric field, air-earth conduction current, and possibly the Ionospheric Potential (IP) in a way that depends on the geomagnetic cut-off rigidity of the location and the altitude. If a dust particle layer is present, GLE events tend to cancel its electrical effects in the ambient atmosphere. This means that the enhancement of the electric field and the reduction of atmospheric electrical conductivity, caused by the ion attachment to dust particles, not only tend to return to their ambient fair weather values, but they can be further modified as if the dust layer was not present. Finally, in terms of dust particles' electrical properties, GLE events tend to modify the ion attachment mechanism, and in principle, the particle net charge, and the electric field "sensed"by them, increase. Nevertheless, since the electrical force magnitude is up to six orders of magnitude less than gravity, the increase of the particles' electrical properties is not sufficient to modify the particle settling dynamics and settling velocities.
查看更多>>摘要：We report the first estimation of Cloud to Ground (CG) lightning activity over the Indian subcontinent. Initial results from the analysis of ground-based data of worldwide lightning location network (WWLLN) over the Indian region are discussed. The CG lightning density is analysed from the quality controlled WWLLN data for three years during 2009-2011. The lightning flash density (LFD) analysis is shown with high and low LFD regions spatially. The LFD is enhanced by 20% in year 2010 and 13% in year 2011 in comparison to LFD in the year 2009 over the eastern sector. Over the west coast (around geo latitude 200 E) there is a 30% increase in LFD in 2010 and 17% increase in 2011. Over the Bay of Bengal, there is an increase of up to 66% LFD at few places in both the years. Aerosols and carbon dioxide (CO2) being the two most significant species in the Earth atmosphere responsible for atmospheric heating and convection are studied for the variations in their concentration during this period. There is an enhancement of 4 ppm in the CO2 concentration over the study region in 2010 and 7 ppm in 2011 corresponding to enhancement in LFD. The Aerosols concentration over Indian mainland has increased up to 50%. Over the Arabian Sea and Bay of Bengal the aerosol optical depth (AOD) is found to decrease 25% where lightning flash density is found to reduce from the previous year. We find positive correlation between LFD-aerosols and LFD-CO2. Overall, there is an increasing trend of atmospheric temperature, LFD, aerosols and CO2. The cloud microphysical effect that may have been impacted due to increase in air temperature, AOD and in concentrations of CO2 in the atmosphere is investigated with this study of lightning discharges.
Seba, Ephrem BeshirNigussie, MelessewMoldwin, Mark B.
9页
查看更多>>摘要：We analyze the role of thermospheric winds on the variability of ionospheric plasma density irregularities for solar maximum periods using ionospheric plasma density profiles from the three Swarm satellites and zonal wind data from the Horizontal Wind Model 14 (HWM14). The results show that the plasma density irregularities are strongest during post-midnight hours compared to pre-midnight hours in the African - American longitude sector and this is associated with an enhancement in eastward zonal wind after midnight. In addition, the occurrence of plasma irregularities are observed to show a westward shift. The zonal wind reversal from westward to eastward during post-sunset hours is found to be very important for the generation and variability of plasma irregularities. In the African - American longitudinal sector, where plasma irregularities are the most intense, the eastward wind is strongest in December solstice than for the other seasons. Moreover, plasma irregularity during the December solstice is comparable to the Rayleigh-Taylor Instability mechanism (RTI) favored equinox seasons. But, plasma irregularities are weakest in the June solstice where the zonal eastward wind over geomagnetic equatorial region is weakest as compared to the other seasons. Zonal wind reversal from westward to eastward around post-sunset hours occurred early for seasons with stronger ionospheric irregularity activity whereas the reversal is delayed for the season with weakest ionospheric irregularity activity in the African - American sector. Our results are confirmations of the theoretical prediction on the role of eastward zonal wind in plasma instability growth rate by Kudeki et al. (2007).
查看更多>>摘要：Field-aligned current (FAC) is one of the most important aspects in the coupling of magnetosphere and the ionosphere. This paper presents a systematic numerical study of the magnetospheric and ionospheric influences on the evolution and modification of FACs, with focus on the role of ionospheric Pedersen conductance and its gradient. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfven waves. During their reflection from the ionosphere, these FACs are modified. The nature of modifications depends on the magnitude and distribution of ionospheric Pedersen conductance. A uniform ionosphere, having a high Pedersen conductance, enhances such a magnetospheric FAC strongly. For conductance-gradients perpendicular to the wave-polarization, FACs are generated after the reflection of simple Alfvenic perturbations, which are not carrying any FACs. A suitable arrangement of ionospheric Pedersen conductance can create a pair of antiparallel FACs, with consequent generation of a strong Pedersen current at the ionospheric boundary. For conductance-gradients along the polarization of the wave, the steady state velocity perturbation assumes an average value of the imposed Pedersen conductance over the entire region after reflection from the ionosphere. This configuration is comparable to the situation where the Cowling conductance operates.
NSTL
Elsevier