Journal of Atmospheric and Solar-Terrestrial Physics

Cosmic ray − global lightning causality

Tue, 06/11/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): O. Okike, A.E. Umahi

Abstract

Many atmospheric processes such as atmospheric ionization, cloudiness, temperature and terrestrial lightning have been attributed to galactic cosmic rays (GCRs) hitting the Earth's atmosphere. While some of these theories linking cosmic rays with Earth's geophysical phenomena have been well addressed with empirical results, there are a lot of open fields in the GCR-lightning hypothesis. Some authors have, for instance, investigated the proposal using regional lightning data (Chronis, 2009). The present study uses global lightning data from the world-wide lightning location network (WWLLN) to test the claim that GCRs are responsible for Earth's atmospheric lightning. Regression and superposed epoch analyses are both employed in this investigation. We conclude that the results are consistent with a causal role of GCRs in lightning strikes.

Global lightning activity and the hiatus in global warming

Tue, 06/11/2019 - 19:10

Publication date: August 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 189

Author(s): Earle Williams, Anirban Guha, Robert Boldi, Hugh Christian, Dennis Buechler

Abstract

Multiple records of global temperature contain periods of decadal length with flat or declining temperature trend, often termed a ‘hiatus’. Towards assessing the physical reality of two such periods (1940–1972 and 1998–2014), lightning data are examined. Lightning activity is of particular interest because on many different time scales it has been shown to be non-linearly dependent on temperature. During the earlier hiatus, declining trends in regional thunder days have been documented. During the more recent hiatus, lightning observations from the Lightning Imaging Sensor in space show no trend in flash rate. Surface-based, radiosonde-based and satellite-based estimates of global temperature have all been examined to support the veracity of the hiatus in global warming over the time interval of the satellite-based lightning record. Future measurements are needed to capture the total global lightning activity on a continuous basis.

Editorial Board

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s):

A statistical study of photospheric magnetic field properties of active regions associated with M- and X-class flares using SDO/HMI vector magnetic field data

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s): Wai-Leong Teh

Abstract

With the aim of understanding the photospheric magnetic field properties of active regions (ARs) that produce M-class or greater flares, physical magnetic parameters of ARs provided by the Space-weather HMI Active Region Patches (SHARP) are examined. A total of 223 flares are collected in 83 ARs, including 31 X- and 192 M-class flares. In this study, twelve SHARP parameters are analyzed, which are the sums of various physical quantities (e.g., magnetic flux, magnetic free energy density, vertical current, current helicity, shear angle, and Lorentz force). For X- and M-class flares, good correlation coefficients (≳ 0.90) are obtained among the seven magnetic parameters, namely, total unsigned quantities of (1) magnetic flux, (2) vertical current, (3) current helicity, and (4) flux near polarity inversion line, as well as (5) total photospheric magnetic free energy density, (6) total magnitude of Lorentz force (TOTBSQ), and (7) area of AR. A threshold for low bound is estimated for each of the seven magnetic parameters based on X-class flares. Only ∼5% of M-flares occur below the estimated thresholds. A time difference (TSF) is calculated between the time when all the magnetic parameter thresholds but TOTBSQ are met (T1) and the time when the flare starts. The TOTBSQ is excluded in the T1 calculation because its value is often missing in the interval of interest. Results show that (1) ∼77% of X-flares occur within 7 days after T1, with an occurrence peak at TSF=2 (∼20% probability), (2) ∼78% of M-flares also occur within 7 days after T1, with an occurrence peak at TSF=4 (∼20% probability), and (3) no major flare occurs after TSF=11. It is found that the GOES soft X-ray peak flux has a very weak relationship with the magnetic free energy density. This weak relationship can be interpreted in terms of the energy partition in a flare. In conclusion, the obtained seven thresholds will be useful for monitoring an AR that has a high potential to produce an M- or X-class flare.

Observed diurnal and intraseasonal variations in boundary layer winds over Ganges valley

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s): E.A. Resmi, P. Murugavel, Gurnule Dinesh, B. Balaji, P.P. Leena, Varghese Mercy, Nair Sathy, Chowdhuri Subharthi, Tiwari Yogesh, Karipot Anandakumar, Thara V. Prabha

Abstract

The diurnal and intraseasonal variability in the surface winds are examined using high resolution measurements during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) Phase III Integrated Ground based Experiment, conducted in the Ganges valley during 2014–15. The yearlong observations of lower boundary layer wind from the Ganges valley are discussed in this study. Wind speed and directions at the surface levels obtained from SOund Detection And Ranging (SODAR) and tower are compared and found, mostly SODAR measurements are consistent with tower during high wind conditions (greater than 4 ms−1) except under weak circumstances. Our analysis revealed that, the mean wind speed found to be a maximum (7.86 ms−1) during the monsoon season in the air layer between 10 m and 200 m level and shows a sharp increase near to the surface (at 20 m level). Analysis also depicts seasonal variations in wind speed are predominant in the lower boundary layer and it is closely linked to the large-scale flow patterns/disturbances. The turbulent kinetic energy (TKE) was found to be maximum at 165 m (0.62 m2s-2) during the pre-monsoon due to enhanced surface heating. The 93% and 75% of the wind speed profiles exhibited unstable conditions in the monsoon and post monsoon conditions. Moreover, the unstable layers are characterized by high wind speed and temperature structure function (CT2)in day time. On large scale, the wind speed gets strengthened (reduced) in the wet (dry) spell in the lower levels with distinct diurnal cycle in the Indo Gangetic Plain. The advection of moisture in the nocturnal periods in connection with the wet spells in the near surface level is observed and the wind speeds in the daytime (above 150 m) are also found to be stronger in the range 3.5–5 ms−1 in the dry spells due to the enhanced mixing. The diurnal cycle is more evident in the dry spells in the lower levels. Rainfall peak found in July 2014 is connected with the quasi-biweekly mode periodicity of 2–16 days and further, power spectrum analysis reveals that the presence of high frequency oscillations of periodicity less than 10 days and between 10 and 20 days in the surface layer parameters.

Aerosol and gaseous pollutant characteristics during the heating season (winter–spring transition) in the Harbin-Changchun megalopolis, northeastern China

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s): Hujia Zhao, Yanjun Ma, Yaqiang Wang, Hong Wang, Zhizhong Sheng, Ke Gui, Yu Zheng, Xiaoye Zhang, Huizheng Che

Abstract

Serious pollution events caused by residential heating activities occur frequently in northeastern China, and these increased particulate matter levels and gaseous pollutants could contribute to both local emissions and regional climate change. In this study, meteorological data, air trajectories and aerosol vertical distributions were used to study the pollutant sources and movement paths during the heating season (winter–spring transition) in the Harbin-Changchun megalopolis, northeastern China. Higher concentration of fine-mode particles (PM2.5/PM10 ∼ 0.70–0.80) and the trace gas SO2 (35–45 μg m−3) could be seem as an indicator of the air quality in the Harbin-Changchun megalopolis during the residential heating seasons, caused by local emissions. The apparent changes of meteorological elements in the high latitude and cold regions over Northeastern China could have important effects on the pollutant formation, secondary transformation, aerosol accumulation and vertical transport over the heating season. The PM2.5 concentrations were highly associated with the SO2 and NO2 from both fossil fuel combustion and biomass burning. The obvious diurnal pollutants variation shown thermodynamic conditions could be considered one of the important environmental elements responsible for residential heating processes. The mixture effect of local emissions and aerosol convective activities were found to contribute to the aerosol extinction and air pollution in the Harbin-Changchun megalopolis. These findings could help to improve our understanding of the association between aerosol pollutants influenced by the anthropogenic activities and the aerosol regional climate effects during the heating season in northeastern China.

Role of winter jet stream in the middle atmosphere energy balance

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s): B.G. Shpynev, D.S. Khabituev, M.A. Chernigovskaya, O.S. Zorkal'tseva

Abstract

We consider physical mechanisms responsible for forming plain-layered jet streams in the winter stratosphere. Unlike the conventional notion about the balance between the energy of the solar UV radiation energy absorbed by the stratospheric ozone within the Hartley band and the energy of loss due to infrared emission from СО2, О3, and Н2О molecules, such a balance is shown not to persist. It is shown that the bias of these energies observed in satellite experiments can be explained by dynamic mechanism increasing the air gravity potential in the tropical stratosphere and forming equator/winter pole baroclinic instability, which generates the jet stream. Jet streams transport energy and pulse from equatorial to polar region and facilitate the descending part of the Brewer-Dobson global circulation. Potential energy release, when the stratospheric jet stream lowers, is ∼1018 W/day; the air mass transported by the jet stream to the winter tropopause region is estimated as being ∼1014 kg/day. Based on the ECMWF ERA-Interim reanalysis data, we analyzed the temporal characteristics of the stratospheric air motion from the region of gravity potential abundance generation in the summer tropical stratosphere to the polar winter tropopause altitudes, where the stratospheric air ends its motion, thus participating in cyclogenesis. Duration of the descending part of the Brewer-Dobson circulation in the winter stratosphere/troposphere averages 50–70 days.

Evaluation of some rain attenuation prediction models for satellite communication at Ku and Ka bands

Tue, 05/07/2019 - 19:10

Publication date: July 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 188

Author(s): K.C. Igwe, O.D. Oyedum, M.O. Ajewole, A.M. Aibinu

Abstract

Propagation of radio waves between terrestrial and earth-space links at frequencies above 10 GHz are adversely affected by weather, especially rain. Rain-induced attenuation is an important propagation effect that has to be considered in satellite communication system design. Prediction of rain attenuation for earth-space links in North Central Nigeria at Ku and Ka bands is investigated using five rain attenuation models: The ITU-R P.618 model, Bryant model, Garcia-Lopez model, Svjatogor model and Simple attenuation model (SAM). The main objective is to determine the optimal rain attenuation prediction models for satellite communication in this region. 33 years (1983–2015) daily rainfall data obtained from the Nigerian Meteorological Agency (NIMET) were used. Three elevation angles were considered: 55° 42.5° and 23°. The results obtained showed that the ITU-R P.618, Garcia-Lopez and Bryant models performed best in this region. Also, attenuation ranged from 14 dB to 16 dB at 55° elevation angle, 15 dB–16 dB at 42.5° elevation angle and 20 dB–22 dB at 23° elevation angle for exceedance time percentage of 0.01% at Ku-band in all the stations. For the Ka-band, attenuation varied between 33 dB and 37 dB at 55° elevation angle, 33 dB and 37 dB at 42.5° elevation angle and between 42 dB and 48 dB at 23° elevation angle for same 0.01% exceedance time percentage. From the values of rain attenuation predicted for 0.01% time exceedance, availability of signal is possible at 42.5° and 55° elevation angles but impossible at 23° elevation angle at Ku-band. At Ka-band, the predicted rain attenuation values for 0.01% time exceedance have shown that availability of signal is impossible at all three elevation angles, which implies total signal fade out during such rainfall events in the region.

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