Journal of Atmospheric and Solar-Terrestrial Physics

Morphologies of the topside ionosphere observed by COSMIC at high-latitudes during the 17 March 2013 magnetic storm

Fri, 07/19/2019 - 19:10

Publication date: Available online 19 July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Pei Chen Lai, William J. Burke

Abstract

The present study considers effects on the topside ionosphere at high-latitude (|MLat| ≥ 60°) during the magnetic storm on 17 March 2013. We divide the day into two segments, with magnetic conditions quiet during the first 6 h and disturbed thereafter, thus allowing comparisons of differences between these two states. The COSMIC data source consisted of 272 electron density profiles (EDPs) measured by COSMIC satellites using Abel inversions that assume the absence of horizontal plasma density gradients. We compared resultant EDPs with predictions of the International; Reference Ionosphere (IRI) model for the same altitudes along individual tangent-point lines. As conditions allowed, we also compared EDPs with densities measured by nearby DMSP satellites. During the pre-storm quiet period, 65 of the sampled 68 EDPs were highly correlated with IRI predictions. The remaining 3 EDPs showed significant irregularities along parts of the 800–200 km altitude range. We divided stormtime 204 COSMIC EDPs into three morphological categories. In the first group, 130 EDPs exhibit shapes similar to IRI-predictions. Of these, 72 (9) had larger (smaller) than predicted magnitudes. The second group consisted of 37 EDPs that showed little variation in magnitude over the designated altitude range. The remaining group had another 37 EDPs marked by significant irregularities. We found that the deepest EDP irregularity resulted from GPS signals passing through a deep plasma density trough observed by DMSP. The trough extended along the equatorward boundary of the evening-side, auroral oval. We suggest that EDP irregularities reflect density gradients along or near EDP tangent point lines.

Investigation of solar cycle dependence of the tides in the low latitude MLT using meteor radar observations

Fri, 07/19/2019 - 19:10

Publication date: Available online 19 July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): A. Guharay, P.P. Batista, V.F. Andrioli

Abstract

Solar cycle dependence of the dominant tides, i.e. diurnal and semidiurnal components in the mesosphere and lower thermosphere (MLT) is investigated from a Southern hemispheric low-latitude station, Cachoeira Paulista (22.7oS, 45oW) using long-term meteor wind observations (1999–2018). Although the long-term variations of the tides in aggregate do not show any significant relationship with the solar activity, the individual seasonal profiles reveal appreciable correlation in equinoxes with maximum in fall and no evident correlation in summer. The diurnal tide seasonal profiles show negative correlation with the solar activity and the semidiurnal tide exhibits both negative and positive correlations that vary with altitude within the MLT. The zonal diurnal tide shows positive correlation with the solar flux in the upper MLT in solar minima. However, the meridional semidiurnal tide reveals negative correlation in solar minima condition. No evident relationship between the tides and solar flux is found in solar maxima condition. Since the present study points out resemblance as well as dissimilarity with a handful of previous investigations, further long-term and coordinated studies are being sought to obtain critical understanding of the persistent enigmatic features.

Analysis of GNSS sensed precipitable water vapour and tropospheric gradients during the derecho event in Poland of 11th August 2017

Fri, 07/19/2019 - 19:10

Publication date: Available online 17 July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Grzegorz Nykiel, Mariusz Figurski, Zofia Baldysz

Abstract

Nowadays, one of the techniques that meets the increasing requirements of meteorologist in terms of monitoring of severe weather events is global navigation satellite systems (GNSS), which can provide information about the tropospheric state independently of the weather conditions and even in real time. In this paper we present the usage of GNSS sensed tropospheric data to monitor sudden and intense weather events. Our analyses were performed on the example of a derecho event in Poland of 11th August 2017. We used GPS/GLONASS observations from 278 GNSS reference stations located in Poland and, using Bernese GNSS Software ver. 5.2, we estimated the zenith tropospheric delays (ZTD) and tropospheric gradients with 5 and 15-min intervals respectively. Next, using meteorological data from the synoptic stations, we estimated the precipitable water vapour (PWV) which gives information about the amount of water vapour in the atmosphere. By applying a dense network of GNSS receivers, we were able to create the PWV, rate of the PWV (ROP), and the tropospheric gradients maps, which in turn allowed us to monitor the derecho event. We also conducted case studies for the selected GNSS stations where a comparison between PWV, reflectivity, and microwave radiometer were performed. During the main phase of the event we obtained the maximum value of PWV equal to 52.1 mm at 20:30 UTC. We also acquired high agreement between the PWV/ROP maps and reflectivity derived from meteorological radars. This applies to both the direction and speed of the phenomena as well as the time and place of the occurrence of the main phase of the derecho. This was possible only owing to the use of data derived from the dense network of the GNSS receivers.

Solar activity imprints in tree ring-data from northwestern Russia

Fri, 07/19/2019 - 19:10

Publication date: Available online 15 July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Elena A. Kasatkina, Oleg I. Shumilov, Mauri Timonen

Abstract

The Sun's role in climate variability is now a subject of debates, especially in the context of understanding contribution of solar forcing to modern global warming. Besides, there are some evidences of the approaching new Grand Solar Minimum with Little Ice Age climatic conditions. This expectation is based on the occurrence of the extended solar minimum of 2006–2009. To investigate the possible Sun-climate connection the regional tree-ring chronology covering the period from 1445 to 2005 was analyzed. A total of 36 timber cores of pine Pinus sylvestris L. were sampled near the northern tree-line at Loparskaya station (68.6 N, 33.3 E), including the oldest living pine with more than 560 years of age. The data were processed using modern methods adopted in dendrochronology (cross-dating and standardization) with the help of COFECHA and ARSTAN programs. The analysis revealed significant cooling events, coinciding with the Spoerer (1400–1540), Maunder (1645–1715), Dalton (1790–1830), and Gleissberg (1880–1910) Grand Solar Minima. The application of MTM-spectrum and wavelet decomposition analysis identified the existence of the main cycles of solar activity (5.4, 11.7 and 22 years) in tree-ring width variations. As possible extraterrestrial forcings of climate change we consider here variations in solar irradiance and cosmic ray intensity modulated by the interplanetary magnetic field. As solar and cosmic ray activity indicators we used the annual sunspot number, geomagnetic aa index and Beˆ10 cosmogenic isotope records. To examine the relationship in time-frequency scale between tree-ring growth and solar activity, the cross wavelet transform and wavelet coherence analysis were applied to the time series. The wavelet coherence analysis identified that the 11 yr and 22 yr periodicities were clearly manifested in the all solar-tree rings connections during and around the Grand Minima of solar activity including the Maunder minimum, when, as is known, sunspots were practically absent. These results confirm the existence of solar activity effect on climate and tree growth above the Arctic Circle and are important for understanding the modern climatic processes.

Numerical study of performance of two lightning prediction methods based on: Lightning Potential Index (LPI) and electric POTential difference (POT) over Tehran area

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Maryam Gharaylou, Majid M. Farahani, Morteza Hosseini, Alireza Mahmoudian

Abstract

The electric POTential difference (POT) and the Lightning Potential Index (LPI) performance in predicting the lightning activity is investigated and the probable relationship between them is examined. These two indices have a similar dependency on microphysical variables such as ice, graupel mixing ratios, and also updraft characteristics within the cloud. Regardless of this similarity, the LPI directly calculated from WRF model is a more favorable parameter for predicting the lightning events in comparison with the POT, which requires an extra package (ELEC) model. Ten years' available data over the Tehran area were reviewed and four thundercloud cases with distinct characteristics (CAPE, time-frequency, intensity) were selected. In order to acquire the associated physical properties, four simulations have been done using the WRF-ELEC model, which is initialized with ERA-Interim data.

The assessment conducted within both quantitative and qualitative themes to verify the potential probability of predicting lightning events. In qualitative evaluation framework, the horizontal distribution of LPI and POT were compared to the locations of lightning occurrence detected by WWLLN (The World Wide Lightning Location Network) data as well as the total lightning data obtained from LIS (Lightning Imaging Sensor) in the innermost simulation domain. This evaluation shows that the horizontal patterns of LPI and POT are well consistent with the locations of lightning occurrence. Moreover, in accordance with acquired values of correlation coefficients, it could be inferred that LPI has a better performance in the Number Of Lightning flashes (NOL) prediction than POT. Statistical review of our simulated data (LPI and POT) is performed to study the variation of LPI and POT which resulted in a good correlation between them and therefore, any information about lightning event using LPI values with less computational cost is preferable in the considered domain. Another comparison was carried out based on the calculated correlation coefficient between the simulated NOL and the NOL recorded by WWLLN that does not show any significant correlation between them for none of the cases. Since WWLLN has no observatory in the studied area, inconsistency of the simulated NOL with real atmosphere is justifiable.

Middle atmospheric planetary waves in contrasting QBO phases over the Indian low latitude region

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Kondapalli Niranjan Kumar, Som Kumar Sharma, Vaidehi Joshi, T.K. Ramkumar

Abstract

The present study primarily focused on the characteristics of the planetary scale waves in the middle atmosphere during different phases of Quasi-Biennial Oscillation (QBO), a dominant oscillation in the low-latitude stratospheric region. The temperature profiles retrieved from the Rayleigh lidar measurements have been utilized for the 11 winter periods between 1998 and 2009 over a low-latitude station, Gadanki (13.5oN 79.2oE). The spectral analysis of temperature anomalies indicates two dominant planetary-scale modes, namely, quasi 12-day and quasi 16-day waves. The existence of these waves in the middle atmosphere is strongly controlled by the westerly and easterly phases of QBO. For instance, the 12-day wave is mainly observed in the QBO westerly phase, while the 16-day wave peaks at two heights; 30–40 km and above 60 km with large spread in the mesosphere due to Doppler shifting in presence of westerly winds. The QBO easterly phase indicates low wave activity with 16-day wave indicating appreciable amplitudes in the upper stratosphere and mesosphere and is absent in the lower altitudes. This indicates that the 16-day wave might be generated through some in-situ mechanism due to gravity breaking or instability in the mesospheric region. Moreover, the refractive index of the two dominant planetary waves are strongly negative in the easterly phase relative to the westerly phase of QBO in the lower troposphere and stratosphere. This indicates the high probability of the planetary wave vertical propagation in the westerly phase of QBO. Therefore, the presented report re-emphasizes the importance of QBO controlling the middle atmospheric dynamics through vertical propagation of planetary scale waves in low-latitudes.

Observations of middle atmospheric seasonal variations and study of atmospheric oscillations at equatorial regions

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Nisha Patel, Som Sharma, Vaidehi Joshi, Prashant Kumar, Narendra Ojha, Kondapalli Niranjan Kumar, Harish Chandra, Gufran Beig

Abstract

The equatorial atmospheric regions are unique and one of the most important parts of the Earth's atmosphere. These regions receive the maximum energy from the Sun, and are highly turbulent and influenced by the processes of the Northern Hemisphere as well as by the Southern Hemisphere. Atmospheric temperature is one the most sensitive parameters and having imprints of dynamical, radiative and chemical processes. Thermal structure, seasonal variability and atmospheric oscillations occurring in the equatorial middle atmosphere have been studied here using temperature profiles retrieved from the Sounding of the Atmosphere using the Broadband Emission Radiometry (SABER) instrument on-board Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite during January 2002 to December 2015 (14 years). In the present work, three geographical locations over the Equatorial latitudes and ±120° longitude have been chosen, considering 5° × 15° latitude-longitude grid between the altitudes ranging from 20 to 100 km. A detailed time series and climatology analyses have been performed over these regions and significant longitudinal differences have been observed. Characteristics of Semi Annual oscillation (SAO), Annual Oscillation (AO) and Quasi Biennial Oscillation (QBO) have been investigated using Lomb Scargle Periodogram and wavelet transform analysis techniques. It has been noted the longitudinal differences in the spectral amplitudes of equatorial oscillations relative to the zonal mean spectrum. The longitudinal asymmetry might be due to the vertically propagating planetary waves. From the analysis, it is also observed that SAO is showing the highest amplitude at 45 km and 75–85 km, and QBO is showing significant amplitude in the lower stratosphere. At higher altitudes, amplitudes of different oscillations (viz. SAO, AO, and QBO) are very weak, and temperatures variations are not revealing any significant pattern. Moreover, from the climatology and time series of the temperature measurements, high temperature (∼260 K) has been noticed at 55–65 km height range. In addition to that, seasonal variations over equatorial regions have been studied and the strength of seasonal differences are found to be about 9 K (summer-winter) at higher altitudes.

Relationships between the solar wind magnetic field and ground-level longwave irradiance at high northern latitudes

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): John E. Frederick, Brian A. Tinsley, Limin Zhou

Abstract

Longwave irradiances measured from two sites at different geomagnetic latitudes show different responses to changes in the east-west component of the interplanetary magnetic field (IMF By). At Barrow, Alaska, geomagnetic latitude 69-70oN, neither downward longwave irradiance from the atmosphere nor upward longwave irradiance from the ground show a significant correlation with By. However, at Alert, Canada, geomagnetic latitude near 87oN, a negative correlation that is marginally significant at the 95% level of confidence exists between By and downward longwave irradiance measured 3 days later. On average, a +3.5 nT increase in By is followed by a daily-mean downward longwave irradiance that is smaller by −0.60 ± 0.60% than would exist for a constant By. Similarly, daily-mean upward irradiance at a lag of 4 days is −0.51 ± 0.30% smaller than would exist otherwise, where error bars denote the 95% confidence range. The difference in upward irradiance corresponds to a surface cooling at Alert of approximately 0.33 ± 0.19 K. These results are qualitatively consistent with a previously proposed mechanism in which the interplanetary magnetic field perturbs the ionosphere-to-ground potential difference and the downward atmospheric current density over limited regions near the geomagnetic poles, altering local cloud properties. We find that the atmospheric longwave emission is altered on a time scale of 3 days, with a change in surface temperature appearing one day later, attributable to the thermal inertia of the surface. When one moves from the geomagnetic latitude of Alert (3° from the north geomagnetic pole) to the latitude of Barrow (∼20° from that pole), any connection between By and longwave irradiance becomes too small to isolate from the natural background variability.

A special issue for the space science of JASTP

Fri, 07/19/2019 - 19:10

Publication date: Available online 22 June 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Wayan Suparta, Mardina Abdullah, Mahamod Ismail

Estimating the role of upper Blue Nile basin moisture budget and recycling ratio in spatiotemporal precipitation distributions

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Megbar W. Birhan, U. Jaya Prakasha Raju, SamuelT. Kenea

Abstract

Upper Blue Nile basin (UBNB) is the water tower of Ethiopia and downstream countries. It contributes significant moisture to the surrounding atmosphere. However, the contribution of the moisture from the basin to the precipitation in the UBNB is not well documented. Therefore, this paper is aimed to estimate the role of UBNB moisture budget and recycling ratio for spatiotemporal precipitation distributions. To this end, we used the European Center for Medium-range Weather Forecast (ECMWF) data from 1979 to 2017. The derived ECMWF results are correlated with in-situ observations with the correlation coefficient of 0.82. During summer season most of the UBNB moisture is converted to precipitation around the central parts of the study area, while in spring it contributes to the southern parts of the study area. Furthermore, the northwest part of the study area is affected by the basins moisture during the autumn season. The calculated recycling ratios for four seasons (summer, autumn, spring, and winter) are 9.70%, 16.33%, 19.01%, and 35.30% respectively with the annual average value of 20.11%. It is evident that the maximum amount of precipitation is captured from the local moisture during the winter season. Generally, UBNB moisture budget had a lesser contribution of precipitation over the study area. It rather contributed significant precipitation to the neighboring countries. Hence, further studies on moisture budget are required to explain this phenomenon in the context of Ethiopia.

Graphical abstract

Morphological study on the ionospheric variability at Bharati, a polar cusp station in the southern hemisphere

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): P.R. Shreedevi, R.K. Choudhary, Yiqun Yu, Evan G. Thomas

Abstract

Morphological features of the quiet/disturbed time variations in the Total Electron Content (TEC) at the polar cusp station Bharati (76.69°S MLAT) during a period of 5 years starting from February 2013 to December 2017 has been studied using GPS TEC measurements. The TEC at Bharati follows a diurnal pattern with its peak appearing close to local noon/magnetic noon during the summer/winter months. A nighttime enhancement in the TEC is seen around the magnetic midnight during winter. The plasma density at Bharati also exhibits semi-annual variation and a strong dependence on solar activity. A comparison of the IRI 2016 model derived TEC and the GPS TEC at Bharati shows significant differences with large underestimation of TEC especially during the nighttime period of the winter months. A two fold difference in magnitude between the GPS and modeled TEC is also observed in the summer months of the high solar activity period of 2013–2015. The response of the TEC to geomagnetic storms is found to depend on the onset time of the storm. We show that the morphological features in the temporal evolution of the plasma density at Bharati vary as the location of Bharati changes from being inside the polar cap, to the auroral region, and to the polar cusp in quick succession in a day. Our results highlight the fact that the dynamic nature of the location of Bharati with respect to the position of the polar cap plays an important role in deciding the plasma distribution at the polar cusp station.

Development of a hybrid classification technique based on deep learning applied to MSG / SEVIRI multispectral data

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Salim Oukali, Mourad Lazri, Karim Labadi, Jean Michel Brucker, Soltane Ameur

Abstract

The approach developed in this paper for the classification of precipitation intensities is based on deep learning of neural network. Multispectral data from the MSG satellite (Meteosat Second Generation) providing information about the cloud's physical and optical characteristics are exploited and used as inputs to a deep neural network model. The model is a combination of CNN (Convolutional Neural Network) and DMLP (Deep Multi-Layer Peceptron) which is learned and validated by comparison with the corresponding Radar data during the rainy seasons 2006/2007 and 2010/2011 respectively. The CNN extracts spatial characteristics from MSG multi-spectral images. Then, the set of spatial and multi-spectral information are used as inputs for the DMLP. The results show an improvement compared to the three other classifiers (Random Forest, Support Vector Machine and Artificial Neural Network). The CNN-DMLP method was also compared to the technique combining the three classifiers (SAR). The results indicate a percentage correct (PC) of 97% and a probability of detection (POD) of 90% for CNN-DMLP method compared to 94% and 87% for of the SAR technique, respectively. In terms of bias, the CNN-DMLP method gives 1.08 compared 1.10 for SAR technique.

Predicting SuperDARN cross polar cap potential by applying regression analysis and machine learning

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Erxiao Liu, Hongqiao Hu, Jianjun Liu, Xuyang Teng, Lei Qiao

Abstract

The cross polar cap potential (CPCP) is one of the primary parameters characterizing the electrodynamic feature of the high latitude ionosphere convection. In this study, we perform a comprehensive investigation of the Super Dual Auroral Radar Network (SuperDARN) CPCP, based on a large database of measurements from 1999 to 2009, and its relationship with various parameters of the solar wind, interplanetary magnetic field (IMF) and geomagnetic indices. Specifically, the IMF clock angle, the IMF Bz, the solar wind velocity, the plasma proton density, AE index, SymH index and Dst index are under consideration. According to the results of the correlation, the input parameters are selected and two models of the CPCP based on the multivariate regression analysis and Back Propagation Artificial Neural Network (BP ANN) algorithm are proposed respectively. The regression and BP ANN models are validated and the accuracy as well as the stability of the models is tested by using independent datasets. The result shows that the root mean square error (RMSE) between the measured and the model values ranges from 3.7 to 6.7 kV and the linear correlation coefficients are close to, or above 0.7. The ANN model is shown to have a better performance than the regression model.

Surface solar radiation and its association with aerosol characteristics at an urban station in the Indo-Gangetic Basin: Implication to radiative effect

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Sunil Kumar, A.K. Srivastava, V. Pathak, D.S. Bisht, S. Tiwari

Abstract

Short-wave incoming solar radiation and aerosol optical characteristics were examined at New Delhi, in the western Indo-Gangetic Basin (IGB) for the period from March 2010 to June 2012 to understand their possible association in different sky conditions along with their radiative implications. During the study period, solar radiation varied between 65 and 624 W m−2, with a seasonal mean of 419 ± 34, 328 ± 32, 308 ± 54 and 306 ± 56 W m−2, respectively in the summer, monsoon, post-monsoon and winter periods. Inter-annually, the magnitude of solar radiation was ∼19% and 23% higher during 2012 as compared to 2011 and 2010. Aerosol optical Depth (AOD) varied between 0.11 and 2.4 (mean: 0.69 ± 0.38) whereas Ångström Exponent (AE) was between 0.46 and 1.81 (mean: 0.8 ± 0.28) during the entire study period. The solar radiation was found to be significantly correlated with the AOD (R = −0.22) and AE (R = −0.45). The mean characteristics of solar radiation and aerosol optical parameters were found to differ significantly in different sky conditions, which were used to examine their possible implications to direct radiative effect (DRE). The DRE at the surface was as high as about −19 W m−2 during clear sky day, which was ∼16 and 48 W m−2 higher than that of haze/foggy and dusty days, respectively.

Investigating extracted total precipitable water vapor from Weather Research and Forecasting (WRF) model and MODIS measurements

Fri, 07/19/2019 - 19:10

Publication date: 15 October 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 193

Author(s): Hossein Hassanli, Majid Rahimzadegan

Abstract

Total Precipitable Water (TPW) vapor value in the earth's atmosphere and its variations are of great importance in atmospheric and climatic studies. Among the most important methods introduced for estimation of TPW are satellite products such as Moderate Resolution Imaging Spectroradiometer (MODIS) and numerical methods such as Weather Research and Forecasting (WRF). The performance of TPW estimation methods are different in various locations and require evaluations. Then, the goal of this study is investigating the performance of estimated TPW from MODIS product (MOD05) and WRF model. In this regard, two infrared (IR) and near infrared (NIR) algorithms of MOD05 were evaluated. Moreover, three nested resolutions of 27, 9, and 3 km of the WRF in 0000 and 1200 UTC were investigated. Mehrabad radiosonde station in the south of Tehran, Iran was considered as the study area. Evaluation of the two selected models was performed using radiosonde measurements of 240 days in 2013 and 2014. Among the nested domains for WRF model, the 3 km model at 0000 UTC provided the best results with determination coefficient (R2) of 0.81 and Root Mean Square Difference (RMSD) of 2.98 mm. Among the MODIS products, MODIS IR showed a better performance with R2 of 0.72 and RMSD of 3.46 mm. In general, the estimated TPW from MODIS-IR and WRF3 showed that WRF has a better performance. Then, the results proved that WRF model can be used in various meteorological conditions for estimation TPW with an acceptable accuracy.

Predicting precipitable water vapor by using ANN from GPS ZTD data at Antarctic Zhongshan Station

Fri, 07/19/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Yingchun Yue, Tao Ye

Abstract

Precipitation plays an important role in human activities, and accurate prediction of precipitation is expected to make the arrangements accordingly, especially in Antarctic area with complicated weather conditions. Since directly forecasting precipitation usually requires a lot of meteorological data, which is difficult to be collected in Antarctic area, the precipitation is usually predicted indirectly by using precipitable water vapor (PWV). The PWV can be calculated by Hopfield model using GPS zenith tropospheric delay (ZTD) data if only the temperature and pressure data is available. In this paper, we adopt the artificial neural network (ANN) with genetic algorithm (GA) to predict the PWV of the Zhongshan Station in 6 and 12 h by four different input schemes, including ZTD, ZTD with real-time meteorological data, PWV, and intrinsic mode functions (IMFs) of PWV. The predicted results show that the worst prediction is got by using ZTD sequences with the correlation coefficient of about 0.50. The results of using ZTD with real-time meteorological data and PWV have approximate correlation coefficient of about 0.80. The best prediction is obtained by using IMFs of PWV sequences to predict 6 h PWV with the correlation coefficient of 0.95.

Validation of the IRI 2016, IRI-Plas 2017 and NeQuick 2 models over the West Pacific regions using the SSN and F10.7 solar indices as proxy

Fri, 07/19/2019 - 19:10

Publication date: Available online 5 June 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Yekoye Asmare Tariku

Abstract

This paper investigates the validation of the performance of the latest versions of the International Reference Ionosphere (IRI 2016), the IRI extended to the plasmasphere (IRI-Plas 2017) and NeQuick 2 models in the estimation of the variation of the Total Electron Content (TEC) over the West Pacific regions during the 2015–2017 years. This has been performed employing the GPS-derived TEC data obtained from stations located at Observation Rock, OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N), Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N). It has been revealed that both the GPS-derived VTEC and modelled (IRI 2016, IRI-Plas 2017 and NeQuick 2 VTEC) variations attain their minima at about 13:00 UT (05:00 LT) and maxima at about 20:00 UT (12:00 LT). Moreover, because of the enhancement of photo-ionization process in the region as a result of exposure of the ionosphere for direct radiation in the summer months, large measured VTEC values are seen in the June solstice months during 2015–2017. It has also been shown that, because of the variation of the Sunspot number (SSN) and solar radio flux 10.7 cm (F10.7), the VTEC variations for both the GPS-derived and models show decrease at transition from 2015 to 2017, with some exceptions observed in the June solstice months. In addition, the root-mean-square deviations (RMSD) between the GPS-derived and modelled diurnal VTEC variations are generally less than 0.5TECU in using both the SSN and F10.7 indices. This shows that all the three models are good in TEC estimation with the IRI-Plas 2017 and NeQuick 2 perform the best on most of the hours, in comparison with the IRI 2016 model with IRI2001 option, especially in using the F10.7 index when the solar activity increases. However, when the solar activity decreases, utilizing the SSN for all the three models (especially for the IRI-Plas 2017 and NeQuick 2) shows the better performance. Moreover, during the geomagnetic storm condition, both the IRI 2016 and IRI-Plas 2017 models with the storm option “on” do not adequately reflect to the sharp increase or decrease of the GPS-derived VTEC values.

Atmospheric anomalies associated with M<sub>w</sub>>6.0 earthquakes in Pakistan and Iran during 2010–2017

Fri, 07/19/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): Munawar Shah, M. Arslan Tariq, Najam Abbas Naqvi

Abstract

Recent advances on satellite-based measurement of different atmospheric constituents at different heights provide sufficient evidences of short and long-term earthquake (EQ) precursors. In this paper, atmospheric anomalies are investigated related to three large magnitude Mw > 6.0 EQs in Pakistan and Iran during 2010–2017 (i.e., January 18, 2011 (Mw 7.2, Southwestern Pakistan), April 16, 2013 (Mw 7.7, East of Khash Iran) and February 07, 2017 (Mw 6.3, Pasni, Pakistan)). For this purpose, satellite based Outgoing Longwave Radiation (OLR), Surface Temperature (ST), Aerosol Optical Depth (AOD) and NO2 are investigated by statistical bounds of median and standard deviation for two months before and one month after the occurrence of each event. We study the spatial OLR anomaly from National Oceanic and Atmospheric Administration/National Center for Environmental Prediction (NOAA/NCEP). Evidences suggest that abnormal atmospheric anomalies occur within one month before the main shock. For example, in case of Mw 7.2 southwestern Pakistan EQ, significant perturbations in daytime OLR are detected up to 21 days before the main shock, justifying the existence of huge amounts of energy over the tectonic lineaments. The OLR anomaly correlated with ST, AOD and NO2 during 15–21 days before the main shock, which may be attributed to the same event. Similarly, the OLR, ST, AOD and NO2 show irregularities before the 2013, Mw 7.7 East of Khash Iran EQ, where all the anomalies occur 9–10 days before the main shock. The anomalous OLR over the epicenter suggests the authenticity of all the temporal perturbations in the atmospheric parameters related to Mw 7.7 (Iran event). Furthermore, the atmospheric parameters are analyzed temporally by the statistical bounds before the Mw 6.3 (Pasni, Pakistan) EQ. All the parameters behave abnormally during 10–15 days following the Mw 6.3 Pakistan EQ and similarly subsequent spatial OLR enhancement over the epicenter may lead to the conclusion of an extensive energy emanation. The anomalies detected are consistent with the processes of stress activation of proxy defects at the Lithosphere-Atmosphere interface in the seismic breeding zone.

Observed response of stratospheric and mesospheric composition to sudden stratospheric warmings

Fri, 07/19/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): M.H. Denton, R. Kivi, T. Ulich, C.J. Rodger, M.A. Clilverd, J.S. Denton, M. Lester

Abstract

In this study we investigate and quantify the statistical changes that occur in the stratosphere and mesosphere during 37 sudden stratospheric warming (SSW) events from 1989 to 2016. We consider changes in the in-situ ozonesonde observations of the stratosphere from four sites in the northern hemisphere (Ny-Ålesund, Sodankylä, Lerwick, and Boulder). These data are supported by Aura/MLS satellite observations of the ozone volumetric mixing ratio above each site, and also ground-based total-column O3 and NO2, and mesospheric wind measurements, measured at the Sodankylä site. Due to the long-time periods under consideration (weeks/months) we evaluate the observations explicitly in relation to the annual mean of each data set. Following the onset of SSWs we observe an increase in temperature above the mean (for sites usually within the polar vortex) that persists for >∼40 days. During this time the stratospheric and mesospheric ozone (volume mixing ratio and partial pressure) increases by ∼20% as observed by both ozonesonde and satellite instrumentation. Ground-based observations from Sodankylä demonstrate the total column NO2 does not change significantly during SSWs, remaining close to the annual mean. The zonal wind direction in the mesosphere at Sodankylä shows a clear reversal close to SSW onset. Our results have broad implications for understanding the statistical variability of atmospheric changes occurring due to SSWs and provides quantification of such changes for comparison with modelling studies.

Linkage of meteorological parameters and anomalous radio propagation profile over Nigeria

Fri, 07/19/2019 - 19:10

Publication date: 15 September 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 191

Author(s): I. Emmanuel

Abstract

The vertical distribution of refractivity gradient is important in determining anomalous propagation condition. Thirty five years of meteorological parameters, obtained from Era-Interim archive of European Centre for Medium-Range Weather Forecasts has been used to analyze and investigated surface meteorological data linked with refractivity gradient aloft altitude across Nigeria. Spatial distribution of surface temperature, relative humidity and refractivity gradient at 0.1 km, 0.5 km, 1.0 km and 1.5 km over Nigeria were plotted. Vertical distribution of temperature, relative humidity, refractivity and refractivity gradient were obtained for some locations across Nigeria. Similarly, spatial distribution of coefficient of determination between surface temperature, relative humidity and refractivity gradient at four different height were estimated. Linear regression were developed to investigate the relationship between surface data and refractivity gradient at different altitude. The result revealed existence of sub refractive, super refractive, and ducting across the country at 0.1 km and 0.5 km however occurrence of ducting and sub refractive disappeared at 1.0 km and 1.5 km. Likewise, the existence of temperature inversion was noticed between surface and 100 m across all the locations except in Lagos. Values of refractivity across the observed locations converged around 0.5 km. Through result of correlation coefficient and statistical parameters, significant linked have been established between surface data and refractivity gradient at different height.

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