Journal of Atmospheric and Solar-Terrestrial Physics最新文献

The eruption of Hunga-Tonga Volcano on January 15, 2022 has stimulated a wide spectrum of atmospheric waves globally. To probe the surface deformation pattern, Sentinel-1 Synthetic Aperture Radar (SAR) data has been analyzed. It has been approximated that an overall area of about 2.47 square kilometres experienced deformation in conjunction with this event. To characterize the atmospheric wave propagation, barometric pressure data from 1814 stations distributed all around the globe have been examined. This study encompassed with the propagation characteristics of the waves over four zones including Indian and Polar regions for the first time using barometric data. Time-series observations indicate that the waves propagated globally multiple times. Within the Indian region, three minor arc passages and one major arc passage were identified. In Japan, two minor arc passages and one major arc were present. Conversely, in North America, both minor and major arc passages were detected, occurring a minimum of three times. Moreover, the attributes of these waves, such as their propagation speed and periodicity, were compared across these four regions. The estimated phase speed and periodicity fall within the ranges of approximately 291–314 m/s and 10–180 min, respectively including Polar Regions. These speed and periodicity measurements of the observed waves suggest that the dominant mode of wave propagation generated during the Tonga volcanic eruption is that of Lamb waves. In addition, a slower propagation phase speed of about 226.6 m/s was identified in Japan which corresponds to Pekeris mode of waves.

The objective of this study is to evaluate the clouds seasonal occurrence characteristics, and to estimate their impact on solar radiation in Mbour, Senegal, West Africa. Here, we use datasets from various sources including: i) observations from the Clouds and Earth's Radiant Energy System satellite sensors, ii) in situ shortwave radiation measurement obtained from the Mbour station, and iii) the outgoing longwave radiation (OLR) obtained from the National Centers for Environmental Prediction reanalysis data. Results show a marked seasonality, associated with high spatial variation in terms of cloud occurrence over Senegal. The maximum cloud occurrences are observed during the wet summer season (June–October), whilst the minimum cloud occurrences are recorded during the long-dry season from November to May. During the monsoon season the cloud activity becomes more intense with a total cloud cover of about 80%, a cloud optical depth of around 7, and a high convective activity illustrated by a low OLR (below 240 W/m²). Likewise, across Senegal a strong north-south gradient of the cloud characteristics is observed. Based on quantitative comparison between cloud occurrence and radiation measurement, results show an important seasonal impact on available solar potential in Mbour. Conversely to the cloud occurrence, the maximum of both direct normal and global solar potentials is recorded during the dry season, coinciding with the period with clean sky. An investigation of the cloud influence on solar radiation on selected study cases indicates a decrease of 60% (80%) for the total (direct normal) radiation during the peak of the summer monsoon season.

The perturbations in the ionosphere due to eight tropical cyclones (TCs), namely Iota, Haima, Harold, Willa, Amphan, Gaja, Vadrah and Bulbul, originated and grown in different oceanic basins, are investigated. Total Electron Content (TEC) data, from Global Positioning System (GPS) TEC receiver in operation at Agartala (AGT) or different International GNSS Service (IGS) stations near the cyclone landfall regions, are used in this study. Despite some differences, the ionosphere responds to all tropical cyclones in an almost similar manner. Though the geomagnetic conditions are quiet and there are no perturbations due to any other geophysical phenomena in the active cyclonic storm stage, in all the cases there is a fall in average vertical total electron content (VTEC) deviations below the monthly mean value either on the landfall day or on the following day or even on just previous day. Decrements in Vertical Total Electron Content are found higher for tropical cyclones over North Indian and South Pacific oceanic basins. Recoveries in vertical total electron content values are slower for cyclones over the North Atlantic and North West Pacific basins. Recoveries in vertical total electron content (VTEC) values are slow for tropical cyclones (TCs) over the North Atlantic and North West Pacific basins. But those over other basins are quick. The longer the track of a tropical cyclone (TC), the higher is the reduction in the vertical total electron content (VTEC) value. A negative correlation exists between the maximum sustained surface wind velocities and the total periods of different TCs and also the difference of lowest average differential VTECs with that on the previous day. The observed anomaly in ionospheric responses might be due to the combined effect of TC-inspired gravity waves, ejection of neutral particles from the terminator of a tropical cyclone (TC) and lightning electric fields. To explain the observed results convective activities during TC, with the help of outgoing long wave radiation (OLR) map, are also taken into account. This study provides the primary results regarding regional characteristics and hence a comparative idea for the responses of the ionosphere to different tropical cyclones (TCs) from different geographical positions on the globe, which needs further comprehensive investigation in future.

Spectral analysis is a technique largely used to study scale size regime of ionospheric plasma irregularities based on in situ measurements, notwithstanding the visual representation of power spectral density (PSD) of a signal is often a source of ambiguity during fitting routines and identification of breakpoints. In this work, a method is proposed in order to mitigate the uncertainties inherent to this process. Here, the spectral behavior of time series fluctuations is alternatively investigated using Detrended Fluctuation Analysis (DFA). The DFA algorithm is a scaling analysis procedure widely applied to estimate the detection of long-range correlation without considering apparent short-range ones. Furthermore, the DFA technique is able to remove trends implicit to the signal and to be applied to non-stationary time series. Using in situ measurements of both ionospheric electron density and electric field fluctuations, it was able to analyze plasma bubbles with scales ranging from 1.66 km to 12.4 m. The results show that DFA and PSD routines provide quite similar spectra, but different spectral indices. On the other hand, the spectra revealed steep slopes wrapping the medium scales, a characteristic also detected in other studies. Besides that, the DFA is less noisy than Fourier spectra, which allows a more precise identification of spectral breakpoints.

The time series of standard phase-height (SPH) and plasma scale-height (PSH) have been updated from a 60-year long-radio-wave measurement of the broadcasting station Allouis (France, 162 kHz). The signal was received at Kühlungsborn (54° N, 12° E, Mecklenburg, Northern Germany).

The statistical analysis of the SPH series shows a significant overall trend with a decrease of 116 m/decade indicating a subsidence of the long-radio wave reflection height of about 700 m. With consideration of a stratopause altitude trend (-70 m/decade) follows an overall mesospheric shrinking of about 300 m over Western Europe.

As expected the time series of SPH shows in its spectrum dominant modes which are typical for the solar cycle, ENSO and for QBO bands indicating solar and lower atmospheric influences. Solar cycle and ENSO (-QBO)-like band-pass show a growing increase of SPH up to 1987, followed by a decrease afterward. We found a strong reduction in the amplitude of the solar cycle band due to the weak solar cycle 24, but an increase in the ENSO band.

For summer months during solar minimum years, and without stratopause altitude trend, a thickness temperature trend of the mesosphere is significant with a trend value of −0.47 ± 0.43 K/decade. The long-term solar variability and the stratopause altitude trend were excluded to determine a more realistic intrinsic mesospheric thickness temperature trend. The overall cooling of the intrinsic mesospheric temperature during 60 years of observation is in the order of 3 K.

The long-term solar variability including the decreasing maximum of last solar cycle, and the stratopause altitude trend have to be excluded in order to determine an intrinsic mesospheric temperature trend, which may be caused by greenhouse gas increase in the middle atmosphere.

Diffuse solar irradiation (H_D) data are essential for the design and management of photovoltaic solar systems, biosphere-atmosphere modeling, and other applications. However, H_D observations are scarce in several locations, especially in tropical regions. Employing hourly diffuse solar irradiation ($H_D^h$) and global solar irradiation ($H_G^h$) data collected between 2002─2003 and 2007─2008 in Alagoas State, Northeast Brazil, this study assesses various modeling techniques. Empirical models, including third-degree polynomial, logistic, sigmoidal, and rational functions, were compared with AI methods such as artificial neural networks (ANN), support vector machine (SVM), and adaptive neuro-fuzzy inference system (ANFIS). Additionally, it explores how solarimetric and meteorological variables impact the performance of these models. The empirical models showed similar performance in estimating $K_D^h(=H_D^h/H_G^h)$ (r² > 0.726, modified Willmott – d_m > 0.704, and RMSD < 0.103), with the third-degree polynomial model standing out. The empirical models had difficulty estimating $K_D^h$ for hourly atmospheric transmittance $\left(K_T^h\right)$ > 0.80, which indicated that they are not able to adequately simulate clear sky conditions, mostly due to surface reflections and clouds at the end of the day. ANN (r² > 0.718, d_m > 0.702, and RMSD < 0.105) showed better precision and accuracy of estimates for a greater number of schemes in relation to SVM and ANFIS (r² > 0.704, d_m > 0.699, RMSD < 0.108) and to empirical models. AI methods were able to represent the complexity of these conditions, with overall performance in estimating $K_D^h$ superior or equivalent to empirical models. This study underscores the significance of exploring diverse methods for H_D estimation, demonstrating promising potential for accurate and reliable estimation of hourly diffuse solar irradiation.

This study investigates the ionospheric response to the December 26, 2019 annular solar eclipse over the southern tip of the Asia region, focusing on Malaysia, Sumatra, and Singapore. Utilizing data from GPS stations and ionosondes along the eclipse path, variations in Total Electron Content (TEC) and ionospheric foF2 parameters were analysed to assess the eclipse's impact. Results indicate a slight northward depletion of TEC, possibly linked to the Equatorial Ionization Anomaly (EIA), with up to −30% of depletions observed across all sites. Time delays in TEC and foF2 parameter responses suggest the influence of recombination and photochemical processes. Differences in depletion percentages between TEC and foF2 parameters may stem from production rate reductions during the eclipse. Post-sunset enhancements in TEC and foF2 parameters suggest the formation of ionospheric plasma blobs associated with Travelling Ionospheric Disturbances (TIDs) during the eclipse. While consistent with trends observed in prior studies, the study's findings highlight regional variations in ionospheric effects. This study enhances our understanding of ionospheric dynamics during solar eclipses and paves the way for further exploration in this area.

Atmospheric fluctuation can be seen everywhere. This study focuses on the record-breaking increase of O₃ concentration during the summer in some sensitive areas in recent years. The findings indicate that in the vicinity of the East Asian continent near western Pacific ocean, when the atmospheric conditions are stable or neutral, it is conducive to the maintenance and propagation of atmospheric oscillations near the height of the pollutant mixed layer (H_PML). Accompanied by the "peak-trough" effect of external gravity wave oscillations, due to the abundant water vapor of the cloud system (there are low pressure or typhoon disturbances in summer) near the large-scale cloud belt at the edge of the subtropical high in the western Pacific, the bright temperature at cloud top shows "light and dark changes" on satellite images, forming a wave-like cloud system. The novelty of this study lies in the fact that atmospheric fluctuations near the H_PML is not only related to the known aggravation of heavy rainfall, but also leads to the additional value-added effect of aerosols. Under static atmospheric conditions, the impact of atmospheric fluctuations near the H_PML on additional rise of O₃ concentration helps us to deepen our understanding of the so-called "entrained ozone (EZ) effect" in the atmosphere. Due to the external gravity waves, the concentration of O₃ increased further. Diurnal variations of solar zenith angle and H_PML are key meteorological factors influencing the significant increase in near-surface O₃ concentration entrainment. The formation mechanism of solar photochemical O₃ is further deepened and supplemented by analyzing the record-breaking increase of O₃ concentration in summer observed in recent years.

Ionospheric modelling is one of the major tools to study the behavior of the ionosphere. Ionospheric models have been useful in predicting the true state of the ionosphere particularly in regions where Global Positioning System (GPS) are not readily available. This research paper aims to study the longitudinal variations and the effects of local time on the total electron content (TEC) recorded in two different sectors (Asia and America) during the ascending, maximum and descending phases of solar cycle 24 (2011–2017) and also to compare its values to IRI-2016, IRI-Plas2017 and NeQuick-2 models in order to evaluate their performances. An hourly interval profile computed on seasonal basis were used to study the behaviors of TEC diurnally and seasonally. A monthly interval error profile plotted on annual basis was also used to investigate the deviations of the models from the GPS values. Our results showed that the peak values of TEC in the Asian and American sectors were recorded around the dawn,06:00UT (13:00LT) and dusk, 18:00UT (15:00LT) respectively. We also affirmed from our results that seasonal/winter anomalies were recorded in all the phases of the solar cycle in both sectors. Equinoctial Asymmetry was also observed to be predominant during different phases of the solar cycle in both sectors except during ascending and descending phases in the Asian and American sectors respectively. Out of the 168 months of data collated for this study, only 162 months of data were available. The IRI-2016, IRI-Plas2017 and NeQuick-2 models have 11.7%, 23.5% and 64.8% better performance in all the months under consideration. Therefore, the NeQuick-2 model had the best performance in both the Asian and American sectors. Finally, from the results of our statistical analysis, Mean Absolute Error (MAE) has ∼3 TECU lower than the Root Mean Square Error (RMSE) values in both sectors and in all the solar cycle phase. Hence, MAE can evaluate the performance of ionospheric models better than RMSE.

The DC global electric circuit (GEC) distributes charge in the lower atmosphere by current flow between “generator regions” (thunderstorms and rain clouds) and “load regions” (distant conductive air), with a timescale defined by circuit properties. Previously, the load has only been modelled by assuming fair weather (FW) conditions, neglecting cloud. As stratiform clouds cover ∼30 % of the Earth's surface, load resistance has been added to represent them, considered to provide semi fair weather (semi-FW) conditions. This increases the GEC timescale by 9 % for stratocumulus, or 33 % for stratus at a lower level. Including mutual capacitance between the outer charged layer and an electrode representing stratocumulus clouds increases the timescale by 35 %, to 8.6 min. These modelled results - the first including the semi-FW aspects - are demonstrated to be consistent with experimentally determined timescales of the real GEC, of between 7 and 12 min, derived from volcanic lightning variations associated with the May 2011 Grímsvötn eruption in Iceland. Accounting for semi-FW circumstances improves the modelled representation of the natural global circuit. Further, the GEC timescale is comparable with cloud droplet charging timescales in the updrafts of extensive layer clouds, suggesting its possible relevance to the microphysical behaviour of stratiform (layer) clouds in the climate system.