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Publication date: Available online 8 August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): J.M. Picone, J. Lean, M. Jones, R.R. Meier

This paper characterizes the semiannual oscillation (SAO) in the received solar radiation (RSR) as a function of latitude for Earth, as a paradigm of a planet with an inclined rotational axis, and studies atmospheric implications. The latitude variations of the RSR SAO amplitude and phase are complex yet systematic. To investigate atmospheric response to the SAO in received solar radiation, we focus on Earth, examining monthly average surface temperature data over a wide latitude range. The latitude variation of surface temperature SAO amplitude and phase show marked similarity to those of the RSR - possible evidence of a residual RSR footprint in the atmospheric temperature and conflicting with current empirical representations of zonal temperature SAO phase and amplitude. For RSR and surface temperature as functions of latitude: (1) properties of SAO are independent of orbital eccentricity, which contributes only a constant global component to local annual oscillation (AO); (2) SAO peaks near equinox at lower latitudes and near solstices at higher latitudes, transitioning in phase over 40° − 60° latitude; and (3) SAO strengths (amplitude relative to local AO amplitude) of RSR and surface temperature are largest near the poles and equator. Also discussed is the presence of SAO in the global average surface temperature while SAO is negligible in the global average RSR. The approximate altitude independence of latitude variations in RSR SAO and the similarity of local surface temperature SAO suggest investigation of a simplified working hypothesis of similar behavior of observed local temperature SAO at higher altitude.

Publication date: 1 November 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 194

Author(s): Niyazi Arslan, Aliihsan Sekertekin

Land surface temperature (LST) is an important parameter that supplies information about the skin temperature of the Earth surface. Remote sensing satellite systems with thermal bands can be used to obtain LST information. One of these satellite systems, namely, Moderate Resolution Imaging Spectroradiometer (MODIS) is mostly utilized in LST studies. One of the problems of obtaining LST from the MODIS data is missing pixels because of the effects such as cloud coverage. This drawback can be encountered by applying Long Short-Term Memory (LSTM) network with one-step-ahead prediction of MODIS data to reconstruct daily LST through the previous data. In this study, LSTM network was applied to the daytime and nighttime MODIS time-series, separately. MODIS LST data (MYD11A1) have the spatial resolution of 1 km × 1 km with 1-day temporal resolution. The selected data range from Day of Year (DOY) 1 in 2017 (01 January 2017) to DOY 59 in 2019 (28 February 2019). MODIS images were processed for the reconstruction of daily LST images concerning an agricultural region in Ceyhan, Adana, Turkey. 82% of data were chosen as the training data while the remaining data were used for testing purposes. The data were reconstructed by feeding the network adding the new data in a moving window in each prediction step. The produced Root Mean Square Error (RMSE) map regarding all reconstruction errors from daytime and nighttime images varied between 2 K to 9 K and 1 K–5 K, respectively. Besides, the coefficients of determination (R2) at a selected pixel of time-series analysis were obtained as 0.894 and 0.905 for daytime and nighttime LST image, respectively. The results revealed that the LSTM network could be used to fix the missing pixels in LST images.

Publication date: 1 November 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 194

Author(s): Pingping Rong, James M. Russell, Benjamin T. Marshall, Larry L. Gordley, Martin G. Mlynczak, Kaley A. Walker

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measured water vapor (H2O) had errors of unknown origin that were recently identified and corrected. The cause of the errors was determined to be unaccounted for spectral out-of-band (OOB) radiance in the H2O channel centered at 6.8 μm arising from ozone emission in the 9.6 μm band. The corrected SABER radiance profiles have been used to produce a long-term H2O data base labeled as version 2.07 (v2.07). Water vapor volume mixing ratio (VMR) vertical profiles are available in the SABER data archive covering the stratosphere and mesosphere extending from near the tropopause at ~100 hPa (~16 km) to the mesopause region at ~ 0.006 hPa (~83 km), and over the time period from 25 January 2002 to the present day. The random error of the v2.07 product is smaller than 4% at 60 km and below, while above this altitude it rapidly increases to 30% (at 80 km), mainly due to low signal-to-noise. The estimated systematic error of SABER v2.07 H2O is about 10–20%. Coincidence analysis between SABER v2.07, MLS v4.2, ACE v3.5-3.6, MIPAS ESA reprocessed v6, and SOFIE v1.3 shows overall excellent agreement in the mean profile with the mean difference being within ±10% in most cases. In the stratopause region SABER H2O tends to be biased high relative to each of the other data sets used for comparisons especially in the SH polar winter where the mean difference reaches 20% or greater. In polar summer above 80 km, SABER H2O is biased low by ~20% compared to the other measurements. SABER H2O therefore reflects the polar winter and spring descent very well but in the summer PMC region the enhancement is weaker than expected. SABER H2O long-term series in the latitude range 50°S-50°N shows close agreement with MLS on a series of pressure levels throughout the stratosphere and mesosphere on inter-annual to decadal time scales. On these time scales also, throughout the years 2002–2005, SABER and MIPAS long-term time series agree well in the equatorial region which serves as an unprecedented validation for this time period. SABER H2O also captures the “tape recorder” phenomenon in the tropical tropopause region very well.

Publication date: 1 November 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 194

Author(s): Lucia Mumo, Jinhua Yu, Brian Ayugi

Analyzing spatiotemporal dynamics of meteorological variables in evolving climate, especially in regions where rain-fed agribusiness is predominant is paramount. In this regard, this study examines the spatiotemporal variability, trend, and magnitude of observed rainfall from 33 synoptic stations during 1979–2017 over Kenya. Non-parametric techniques like Mann–Kendall test, Sequential Mann-Kendall (SMK), and Sen's slope estimator (SSE) were deployed in assessing trend, change points, and magnitude. Results indicate that significant net change of monthly total rainfall mean is observed in May and December. Boreal spring and annual rainfall are insignificantly diminishing at a rate of −1.58 and −0.93 mm/year respectively. During boreal autumn, rainfall is insignificantly increasing at a rate of 1.48 mm/year. High interannual variability was observed, but no abrupt change was recorded during the study period. Spatial distribution of trend reveals dynamic variations from station to station. Amidst boreal spring (autumn), 27 (29) of stations considered had negative (positive) trends wherein 4 (8) stations recorded significant trend at α ≤ 0.01, respectively. At the annual scale, 10 (23) of the stations reported positive (negative) with 1 (5) significant trends at α ≤ 0.01, respectively. At all-time scales, stations at lower eastern and northeastern parts of the country reported a negative trend. Spatial decadal analysis portrays anomalous dry event over the study domain with the first decade being the wettest during boreal spring. To date, anomalously wet conditions exist throughout the country except lower eastern parts during boreal autumn. Comprehensive knowledge about variability, trend, and change point in precipitation is of unprecedented interest to scientists since they are prerequisites for developing effective contingency strategies to curb the impacts of climate change and future preparedness.

Publication date: 1 November 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 194

Author(s): Yuri P. Galuk, Irina G. Kudintseva, Alexander P. Nickolaenko, Masashi Hayakawa

We numerically model the ELF radio wave scattering by a localized non-uniformity in the mesosphere conductivity characterized by a 25–30 km reduction of conventional profile from 70 to 80 km altitude. The disturbance is axially symmetric; it depends on the radius according to the Gaussian law of 1 Mm scale. The complex characteristic electric and magnetic heights are found by solving the Riccati equation. These heights are used in the 2D (two dimensional) telegraph equations (2DTE) when computing the ELF fields in the Earth–ionosphere cavity. The field source is located at the point (10° S; 0° E), the non-uniformity is positioned above the North Pole, and the observer moves across the entire surface of the Earth. Spatial distributions were computed of the vertical electric field amplitude in both regular and non-uniform cavity. Comparison of these data allowed us to single out the reflections from the localized non-uniformity. It is shown that interference takes place at an arbitrary observation point between direct wave and the wave reflected from the non-uniformity. Computational data might be interpreted by secondary currents induced in the non-uniformity by the incident radio wave. There are two types of secondary sources. The first one is a “monopole” radiating symmetrically in all directions. Spatial distribution of the field from this source coincides with the distribution of corresponding Schumann resonance mode at a particular frequency. The other secondary source is of “dipole” type, which has a cosine radiation pattern with the maximum oriented along the source – non-uniformity line. Its spatial distribution coincides with the derivative of the corresponding Schumann resonance mode eigen-function on the distance. Model data obtained will facilitate interpretation of experimentally observed seismogenic Schumann resonance signals.

Publication date: 15 October 2019

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

Author(s): Hyuck-Jin Kwon, Khan-Hyuk Kim, Geonhwa Jee, Ho Jin, Hyomin Kim, Jehyuck Shin, Seungah Lee, Jong-Woo Kwon, Jeong-Han Kim, Changsup Lee, Marc Lessard

We examined wave activities in the Pc5 frequency band (~2–7 mHz) using the magnetic field data from five Antarctic stations, which are AGO3 (72.5° S Altitude-Adjusted Corrected Geomagnetic latitude), South Pole (SPA, 74.6° S), McMurdo (MCM) and Jang Bogo Station (JBS, 80° S), and Dome C (DMC, 89.1° S), during 2017. Pc5 waves at AGO3 and SPA show characteristics associated with Kelvin-Helmohltz instability on the magnetopause and substorm activities, under closed field lines conditions. The local time and seasonal dependence of Pc5 wave activities at polar cap stations (MCM, JBS, and DMC) are significantly different from those at AGO3 and SPA. These indicate that the generation mechanism of Pc5 activities in the open field line region at polar cap is different from that in the closed field lines. We suggest that polar-cap Pc5 is generated by ionospheric current variations produced by solar dynamo between solar wind plasma and geomagnetic field.

Publication date: 1 November 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 194

Author(s): Olexandr Lednyts’kyy, Christian von Savigny, Miriam Sinnhuber, Naomoto Iwagami, Martin Mlynczak

Electronically excited states of molecular and atomic oxygen (O2 and O) are coupled with each other as well as with the ground states of O2 and O in the Multiple Airglow Chemistry (MAC) model representing the oxygen airglow and the oxygen photochemistry in the upper Mesosphere and Lower Thermosphere region. The MAC model couples seven O2 and three O states and was developed on the basis of in situ measurements from the ETON (Energy Transfer in the Oxygen Nightglow) campaign employed to tune rate values of unknown or poorly constrained processes. The same rate values are applied in the MAC model verified and validated on the basis of the in situ measurements obtained during the WADIS-2 (WAve propagation and DISsipation in the middle atmosphere), the WAVE2000 (WAVes in airglow structures Experiment, 2000) and WAVE2004 campaigns. Data sets measured using devices aboard the WADIS-2 rocket are considered to be self-consistent because the MAC retrievals of a concentration profile of O in the ground state ([O(3P)]) can be based on these data sets only. The measuring sites of the in situ data sets from the WAVE2000 and WAVE2004 campaigns are collocated with those of remotely obtained data sets, and these data sets are combined for the MAC retrievals. O2 precursors responsible for the oxygen green line emission, emissions in the Atmospheric band and the Infrared Atmospheric band are identified and confirmed by calculations with the validated MAC model.

Publication date: 15 October 2019

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

Author(s): Teresita Heredia, Flavia M. Bazzano, Rodolfo G. Cionco, Willie Soon, Franco D. Medina, Ana G. Elias

Precipitation and temperature over Tucuman (26.8°S, 65.2°W), a province located in the Northwestern region of Argentina, is analyzed for the interval 1889–2018 in search of any plausible statistical associations with impacts and responses from solar variability. The aim of the study was to contribute data to the controversial issue of climate variations in response to both anthropogenic and natural forcings. The long-term behavior of Tucuman climatic series involves overall warming and augmented precipitation tendencies, possibly linked to the increasing greenhouse gases concentration or even other local man-made factors like increasing urbanization. In addition, we identified sporadic ~4 and ~8-year periodicities, and a ~20-year oscillation after the 1950–1960's. Based on the physical hint that bidecadal periodicities detected in climate parameters are probably not linked to the solar 11-year-like irradiance cycles, we expand our scope of investigations to include another effect which has been recently considered in the dynamics of large rivers as “the planetary hypothesis of the solar cycles”. This new hypothesis supposes that the barycentric dynamics of the Sun could be involved in modulations of the intrinsic solar magnetic and radiative output cycles and therefore Earth-bound climatic responses. Thus, we present a wide-ranging statistical analysis of correlation, cross spectrum, and coherence between Tucuman's climatic series and solar orbital parameters, including also the analysis of hemispheric mean temperatures. Our results show significant coherence at the ~20-year cycle, which is clearly present in the Sun's barycentric dynamic that could in turn be linked to some features of the quasi-decadal solar activity variations.

Publication date: 15 October 2019

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

Author(s): Bing Yang, Eric Donovan, Jun Liang, J. Michael Ruohoniemi, Kathryn McWilliams, Emma Spanswick

A series of statistical and event studies have demonstrated that the motion of patches in regions of Patchy Pulsating Aurora (PPA) is very close to, if not exactly, E×B convection. Therefore, 2D maps of PPA motion provide us the opportunity to remotely sense magnetospheric convection with relatively high space and time resolution, subject to uncertainties associated with the mapping between the ionosphere and magnetosphere. In this study, we use THEMIS ASI (All Sky Imager) aurora observations combined with RBSP electric field and magnetic field measurements to explore convection dynamics during storm time. From 0500 UT to 0600 UT on March 19 2015, auroral observations across ~4 h of magnetic local time (MLT) show that increases in the westward velocities of patches are closely related to earthward flow bursts in the inner plasma sheet. Together with the meridian scanning photometer (MSP) data, this suggests that the increase in the westward velocities of PPA patches is caused by earthward-moving ion injection structures carried by the fast earthward flows.

Publication date: 15 October 2019

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

Author(s): Hui Zhu, Yuri Y. Shprits, M. Spasojevic, Alexander Y. Drozdov

New wave frequency and amplitude models for the nightside and dayside chorus waves are built based on measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument onboard the Van Allen Probes. The corresponding 3D diffusion coefficients are systematically obtained. Compared with previous commonly-used (typical) parameterizations, the new parameterizations result in differences in diffusion rates that depend on the energy and pitch angle. Furthermore, one-year 3D diffusive simulations are performed using the Versatile Electron Radiation Belt (VERB) code. Both typical and new wave parameterizations simulation results are in a good agreement with observations at 0.9 MeV. However, the new parameterizations for nightside chorus better reproduce the observed electron fluxes. These parameterizations will be incorporated into future modeling efforts.

Publication date: 15 October 2019

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

Author(s): M. Pazos, B. Mendoza, P. Sierra, E. Andrade, D. Rodríguez, V. Mendoza, R. Garduño

To assess the effect of geomagnetically disturbed days on the amplitudes of the first three modes of the Schumann Resonance (SR), we analyzed 14-day periods of data around the day of a geomagnetic storm (GS) event. We considered Dst indices lower than ~ −70 nT corresponding to moderate to severe geomagnetic storms. To compare the behavior of the SR signal between days without disturbances in the geomagnetic field (quiet days) and days when a GS occurred (disturbed days), we analyzed data for the years 2015–2017 finding five 14-day periods of SR recorded data that were adequate to perform the analysis. In all cases we found a statistically significant increase (>1 sigma) during the geomagnetically perturbed days in the averaged amplitude of the three main SR frequencies of the horizontal magnetic field components. Such increase may be affected by other natural phenomena, such as lightning activity, measured by a local electric field monitor, or earthquake occurrence. We used data of a SR station located in Coeneo, Michoacán, México (geographic coordinates 19° 48′ 19″ N, 101° 41′ 39″ W; magnetic coordinates 29° N, 174° W; 1964 m asl).

Publication date: 15 October 2019

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

Author(s): Elhadi Takka, Aichouche Belhadj-Aissa, Jianguo Yan, Biao Jin, Azzedine Bouaraba

To guarantee safety-critical implementation of Algerian Satellite-based Augmentation Systems (SBAS), a comprehensive study of the impact of space weather on Global Navigation Satellite Systems (GNSS) over this region is necessary. In this work, three typical ionospheric algorithms: inverse distance weighting (IDW), kriging, and planar-fit were applied on GPS dual-frequency data from seven GPS stations spread over Algerian territory during three major geomagnetic storms of different intensity in addition to a quiet geomagnetic period. The performance of these ionospheric algorithms was investigated based on the broadcast ionospheric vertical delay (Grid Ionospheric Vertical Delay, GIVD) and its corresponding confidence bound error (Grid Ionospheric Vertical Error, GIVE) at two Ionospheric Grid Points (IGPs): (35°N, 5°E) and (30°N, 5°E), located in the Algerian mid-latitudes. The obtained GIVDs were compared to their corresponding delays estimated at nearby user stations as a first reference and to EGNOS messages as a second reference. In addition, the Global Ionospheric Maps (GIMs) from the International GNSS Service (IGS) was incorporated in the analysis. Our results indicate that the studied models provided equivalent accuracy even though kriging slightly outperformed the other models in most of the cases of study. The EGNOS model showed less agreement with the ground truth data during 2013 and 2015, while in 2017 became more accurate after the upgrade. The analysis of estimated GIVEs shows the ability of the three ionospheric models to protect and to safely bound GIVD errors while kriging is intended to provide better availability of Algerian SBAS. In addition, EGNOS GIVEs exhibit effective protection of users at the edge of its service area.

Publication date: Available online 23 July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): Jiangnan Li, Chenghui Ding, Fangzhou Li, Wenshi Lin, Yerong Feng

The WRF model was adopted to perform simulations of Typhoon (TC) Sarika (2016). Two local (QNSE and MYJ) and three nonlocal (YSU, ACM2, and GFS) closure Planetary boundary layer (PBL) schemes were selected to perform five groups of simulation tests. (1) PBL schemes have a minor influence on TC track but exert a major influence on both the intensity and structure of TC. TC track, intensity, and structure simulated according to the nonlocal PBL schemes are close to the observations, while the TC intensities simulated by the local PBL schemes are slightly higher than the actual observed value. The nonlocal GFS scheme generates the best simulation result. (2) The TC intensity is closely related to variations in the TC structure. Of these schemes, the TC simulated by the local QNSE scheme has the largest intensity, the smallest eye zone, a complete eyewall, the strongest convection, the largest reflectivity, and the strongest tangential wind. (3) Differences in the TC intensities occur under the joint action of the thermal and dynamic factors. Regarding the local closure schemes, the simulated values of the surface enthalpy flux, water vapor flux, and momentum flux are slightly higher and the TC can be stronger accompanied by a higher PBL, stronger entrainment at the top of the PBL, and more intense vertical mixing. Moreover, more intense vertical mixing can bring surface energy into the upper air, resulting in the development of deep convection in a stronger TC, an intensified warm core structure, and a higher warm center.

Publication date: 15 October 2019

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

Author(s): Brentha Thurairajah, Scott M. Bailey, Mark E. Hervig

High-latitude northern hemisphere summer mesospheric gravity wave (GW) activity at PMC altitude (82–86 km) is analyzed from nine years (2007–2015) of Aeronomy of Ice in the Mesosphere (AIM) satellite observation. GW activity is characterized in terms of potential energy per unit mass. A new method is proposed to convert the Ice Water Content (IWC) in Polar Mesospheric Cloud (PMC) observed by the Cloud Imaging and Particle Size (CIPS) experiment on the AIM satellite to temperature using a simple model. These are used with temperatures from the Solar Occultation for Ice Experiment (SOFIE, also onboard the AIM), to derive daily averaged GW potential energy in the northern hemisphere summer. July monthly averaged GW potential energy indicates no relation to the 11-year solar cycle. Daily averaged values indicate a large variability in the 27-day GW oscillation, with positive, negative or no correlation with the 27-day solar rotation during individual summer seasons. However, a superposed epoch analysis using SOFIE GW anomalies indicate a significant negative response to the 27-day solar rotation with a lag of 8–12 days. This 27-day GW response may be related to similar oscillations in the wind, but the exact cause of the 27-day signal in the GW activity is not yet understood.

Publication date: 15 October 2019

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

Author(s): Lei Wang, Hao Wang, Zhiwei Heng

An adaptive fast-recognition warning algorithm for severe weather using ground-based Doppler radar and Tropical Rainfall Measuring Mission (TRMM) sensor data is proposed for different seasons, regions and topography conditions in the East and South China Seas. An improved regional segmentation method and the Thunderstorm Identification, Tracking, Analysis and Nowcasting (TITAN) algorithm were applied to identify three-dimensional strong storm cells and their physical features. Multiple logistic linear regression was used to establish a probabilistic warning model for strong convective weather, such as hail and lightning. Doppler radar identification and warning experiments were carried out for a strong squall line near the East China Sea and a supercell storm near the South China Sea. The experimental results showed that the proposed method has higher identification accuracy based on the azimuth and distance than the traditional algorithm. Moreover, the false negative and false report rates of the proposed method are low, which helps to quickly identify and warn against severe weather and protect lives and property.

Publication date: 15 October 2019

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

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

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.

Publication date: 15 October 2019

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

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

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.

Publication date: 15 October 2019

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

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

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.

Publication date: 15 October 2019

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

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

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 Be^10 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.

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

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.