查看更多>>摘要：This paper studies the electric field parameters of negative cloud-to-ground (CG) lightning flashes in the Bogota savanna (a large plateau located in central Colombia), and its comparison with other regions. This work is the first of its kind in the country where the parameters of lightning-generated electric fields are analyzed in detail. A total of 329 CG lightning flashes had been examined. These flashes were recorded within 4-250 km from the measuring station during the period August-November 2016. From observations, negative CG flashes comprised 93% of total events registered. It has been found that negative lightning discharges occurred along the plateau (4250 km2 at 2550 m altitude) exhibit some different characteristics compared with measurements carried out in several regions (tropical, subtropical and temperate latitudes). In this study, it was found that 64.7% of the negative CG flashes are multiple strokes with an average multiplicity of 2.58 strokes per flash. In addition, the mean interval between 789 negative return strokes (306 first- and 483 subsequent strokes) was 61.3 +/- 51.9 ms, while the arithmetic mean of the total duration for 198 multiple-stroke flashes was 149.5 ms. Other lightning flash features such as relation between the interstroke interval and the return stroke order, the ratio of the subsequent stroke peak field to the corresponding first one and the maximum multiplicity are also analyzed.
查看更多>>摘要：The characteristics and driving mechanisms of Elevated Stratopause Events (ESEs) are examined in simulations of the ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry-climate model under present and projected climate conditions. ESEs develop after sudden stratospheric warmings (SSWs) in boreal winter. While the stratopause descends during SSWs, it is reformed at higher altitudes after the SSWs, leading to ESEs in years with a particularly high new stratopause. EMAC reproduces well the frequency and main characteristics of observed ESEs. ESEs occur in 24% of the winters, mostly after major SSWs. They develop in stable polar vortices due to a persistent tropospheric wave forcing leading to a prolonged zonal wind reversal in the lower stratosphere. By wave filtering, this enables a faster re-establishment of the mesospheric westerly jet, polar downwelling and a higher stratopause. We find the presence of a westward-propagating wavenumber-1 planetary wave in the mesosphere following the onset, consistent with in-situ generation by large-scale instability. By the end of the 21st century, the number of ESEs is projected to increase, mainly due to a sinking of the original stratopause after strong tropospheric wave forcing and planetary wave dissipation at lower levels. Future ESEs develop preferably in more intense and cold polar vortices, and tend to be shorter. While in the current climate, planetary wavenumber-2 contributes to the forcing of ESEs, future wave forcing is dominated by wavenumber-1 activity as a result of climate change. Hence, a persistent wave forcing seems to be more relevant for the development of an ESE than the wavenumber decomposition of the forcing.
查看更多>>摘要：The exhalation of geochemical entities from soil to air is significant to understand Lithosphere-Atmospheric relationships. Some of these geochemical entities are capable of modifying the lower atmosphere, and they are employed in various studies. Radon is one of the geochemical gasses widely recognized as a dominant ionization source in near ground regions of the troposphere. The steady state Rn transport equation is considered in many cases for estimating Rn migration from soil to air on the condition that the time evolution is ignored. A method is proposed for estimating radon space-time transport from soil to air. This is achieved by solving the radon transport equation in soil with special boundary conditions. Similar results are obtained with some experimented models, as well as reported radon values in literature for some set of parameter combinations. Strengths and limitations of the method are discussed. The model is useable to study Lithosphere-Atmosphere relationships. It can also be significant in other studies like the Global Electric Circuit or Seismo-Ionospheric studies.
Nandan, RenjuRatnam, M. VenkatKiran, V. RaviNaik, Dinesh N....
9页
查看更多>>摘要：The phase of clouds plays a vital role in determining how clouds interact with the radiation. In this study, long-term radiosonde observations have been used to detect cloud layers and the liquid water path (LWP) is retrieved. The detected cloud layers are verified with the independent observations. All types of clouds shown similar diurnal variation. High occurrence of mixed clouds is observed in all the seasons. The retrieved LWP of liquid water clouds is in good agreement with those obtained from MODIS and ERA5. LWP estimated can be effectively used in various investigations in the absence of any direct observations.
查看更多>>摘要：This study is focused on studying the long-term trend of the diurnal temperature range (DTR) in three temperature zones in Sri Lanka using daily maximum and minimum temperature data set for the recent 33-year (1985-2017). We investigate the potential reasons for the long-term trend in the DTR by studying the response of the DTR to Total Cloud Cover (TCC) and rainfall on a seasonal basis. On an annual basis, results indicate that the DTR significantly decreased per decade by -0.14 degrees C, -0.16 degrees C, and -0.18 degrees C over the high elevation temperature zone (HT), low-elevation temperature zone one (LT-2), and low elevation temperature zone two (LT-2), respectively. The annual decreasing trend of DTR in three temperature zones is mainly due to the larger increase in minimum temperature over the HT (0.13 degrees C/decade), LT-1 (0.23 degrees C/decade), and LT-2 (0.14 degrees C/decade) zones than the maximum temperature from 1985 to 2017. Furthermore, a decreasing trend in DTR is observed during the southwest monsoon (SWM), first inter-monsoon (FIM), second inter-monsoon (SIM), and northeast monsoon (NEM) seasons, where the most prominent decreasing trend in HT, LT-1, and LT-2 is seen in NEM (-0.19 degrees C/decade), SIM (-0.24 degrees C/decade), and SWM (-0.40 degrees C/decade) seasons, respectively. The strong inverse correlation between the DTR and TCC in all seasons indicates that increasing TCC influences the decrease in DTR over the HT, LT-1, and LT-2 zones. Concomitant increasing trends in rainfall during NEM, FIM, and SIM seasons may be one of the possible causes of the DTR decreases in the aforementioned seasons over three temperature zones in Sri Lanka.
Roberto, M.Abalde, J. R.Fagundes, P. R.Bolzan, M. J. A....
16页
查看更多>>摘要：We present and discuss the ionospheric F-region observations from equator to the equatorial ionization anomaly (EIA) regions over the South American sector during an intense space weather event occurred between 27 and May 29, 2017. During this geomagnetic storm, the symmetric-H (SYM-H) reached a minimum of -142 nT at similar to 0700 UT on May 28, 2017. For this investigation, we analyze the vertical total electron content (VTEC) observations from a chain of nearly 120 Global Positioning System (GPS) stations. Magnetometer measurements obtained at two stations in the low latitude regions are also presented. The observations do not indicate prompt penetration electric field (PPEF) effects in the VTEC variations. Magnetometer's observations over Cuiab'a (CBA) and Cachoeira Paulista (CXP) in central west and south parts of Brazil, respectively, have shown a strong crosscorrelation with SYM-H in the period between 3 and 48 h. The results also show positive ionospheric storm phase during the recovery phase on May 28, 2017. Positive effect during the recovery phase of the geomagnetic storm is possibly associated with effects of disturbances winds. During the recovery phase, a strong intensification of the EIA took place, possibly related to an additional ionization effect. The VTEC values show differences between the west and east sectors. This indicates that the EIA crest is stronger in the east sector than in the west sector, possibly due to the combination of disturbance wind effects and geomagnetic field geometry where in the east sector the field lines are more inclined.
查看更多>>摘要：It is investigated theoretically the nonlinear down-conversion of powerful extremely low frequency (ELF) modulated acoustic wave beams at the carrier frequencies 1-20 Hz into ultra-low frequency (ULF) acoustic waves at the frequencies 0.01-0.1 Hz under the propagation upwards within the atmosphere and ionosphere. The approximation of the slowly varying profile is used. It is shown that under a fixed value of the integral power of the initial acoustic ELF beam there exists the optimal value of the initial transverse width where the maximum down-conversion is realized. The different types of the modulation are considered, namely the simplest twofrequency modulation and multifrequency noise-like one. The using of the complex multifrequency modulation results in the increase of the efficiency of the down-conversion within the ionosphere E- and F-layers.
Ehsan, MuhsanAbbas, AyeshaShah, Munawarde Oliveira-Junior, Jose Francisco...
11页
查看更多>>摘要：The ionospheric monitoring satellites aid in correlating the lithospheric variation in ionosphere through Lithosphere-Atmosphere-Ionosphere coupling (LAIC) over the epicenter of future earthquake (EQ). In the present paper, we studied variations in ionosphere associated to two large magnitude EQs (M-w > 6.5) and low epicentral depth EQs of less than 12 km in Plasma Density (PD), Slant Total Electron Content (STEC) and Electron Temperature (ET) of European Space Agency's (ESA) Swarm-three satellites (Swarm-A, -B, and -C). These anomalies are investigated in the Swarm data for 60 days before/after each main shock. The anomalies are detected by statistically implemented median (M) and standard deviation (sigma) method within the Dobrovolsky's area. In order to exclude the geomagnetic perturbations, we have selected the ionospheric data in quiet geomagnetic conditions. Anomalous variations in Swarm-A data occur in ET and STEC for the USA event, and similarly, significant perturbation is clear in STEC of Swarm-B before the M-w 6.5, USA. In case of Swarm-C, no clear anomalies associated with the USA event. Furthermore, Swarm-A, -B and -C have abnormal post-seismic PD, STEC and ET responses to the M-w 6.7 Turkey EQ in the form intensive perturbations beyond the upper bound. We also study the atmospheric data over the epicenters in the form of Outgoing Longwave Radiation (OLR), Relative Humidity (RH), Surface Temperature (ST), and Air Temperature (AT) to support the Swarm observations. RH and ST show pre-seismic atmospheric anomalies before the USA EQ in the same anomalous time period as Swarm satellites. While, OLR, ST and AT have post-seismic atmospheric anomalies after the Turkey EQ within 15-20-day period. The precursors chain from the lithosphere to the atmosphere, followed by the ionosphere are highlighted at different altitudes. The variations window for Swarm satellites and atmospheric indices are 5 days prior to USA main shock and one month after the Turkish EQ. Moreover, this study also aims to study the caliber of Swarm satellites for indicating seismo-ionospheric irregularities, which need more studies to delineate the LAIC hypothesis for future EQ.
查看更多>>摘要：The Sistan Basin in Southwest Asia has been identified as one of the most active sources of dust and windiest terrestrial environments in the world. In this paper, atmospheric analysis of 7 severe dust storms in the Sistan and the Hamoun Lake Basin region during the past two decades was performed. The national center for environmental protection and national center for atmospheric research (NCEP-NCAR) data were used for synoptic analysis of dust events. The locations of low and high pressure systems which were responsible for occurring the dust events were identified and dust plumes routes were presented. The atmospheric analysis results demonstrated that the high-pressure systems over the Caspian Sea and surrounding areas and low-pressure systems over the Indian subcontinent and surrounding areas interactions result in northerly, westerly, and northwesterly winds over the Sistan region, and caused the dust events in this area and transport of dust plumes to east and southeast area. Hamoun Lake Basin in Iran, located in southern and southwestern parts of Afghanistan, and western, northwestern, and central Pakistan are more affected by dust events than other parts of Sistan. An investigation of the areas that were affected by dust plumes showed that southern and southwestern parts of Afghanistan and western Pakistan have the highest AODs and dust load at the surveyed events. The most intense dust activity in Sistan occurs during summertime and based on the results, the maximum amount of dust load reaches 5 gm( -2) in the region in some cases.
查看更多>>摘要：We investigate stochastic acceleration of electrons moving through a chaotic electrostatic field (CEF). Acceleration mechanism is based on irregular scattering of electrons experiencing random pulses in the CEF. Despite the fact that the pulses have random values and orientations, a specific stochastic acceleration of electrons occurs. This acceleration mechanism is analogous to the well-known second-order Fermi acceleration. It can act in various media, where random inhomogeneities create a chaotically distributed electric field. In this paper the phenomenon is investigated specifically for thunderclouds, where the CEF is formed by randomly distributed charged hydrometeors and ions. We show that acceleration process is threshold: the electron flux is accelerated, if the mean CEF value exceeds a certain threshold value, and decelerated otherwise. Accelerated electrons can form the avalanche of relativistic electrons, producing intense bremstrahlung gamma ray radiation. Proposed stochastic acceleration of electrons in the CEF complements second-order Fermi acceleration, expanding its application to static chaotic fields.
NSTL
Elsevier