The influence of geomagnetic activity on mesospheric summer echoes in middle and polar latitudes

Abstract. The dependence of mesospheric VHF radar echoes during summer months on geomagnetic activity has been investigated with observation data of the OSWIN radar in Kühlungsborn (54° N) and of the ALWIN radar in Andenes (69° N). Using daily mean values of VHF radar echoes and of geomagnetic activity indices in superimposed epoch analyses, the comparison of both data sets shows in general stronger radar echoes on the day of the maximum geomagnetic activity, the maximum value one day after the geomagnetic disturbance, and enhanced radar echoes also on the following 2–3 days. This phenomenon is observed at middle and polar latitudes and can be explained by precipitating particle fluxes during the ionospheric post storm effect. At polar latitudes, the radar echoes decrease however during and one day after very strong geomagnetic disturbances. The possible reason of this surprising effect is discussed.

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Investigation of Polar Mesospheric Summer Echoes Using Linear Discriminant Analysis

Remote Sensing ◽

10.3390/rs13030522 ◽

2021 ◽

Vol 13 (3) ◽

pp. 522

Author(s):

Dorota Jozwicki ◽

Puneet Sharma ◽

Ingrid Mann

Keyword(s):

Discriminant Analysis ◽

Linear Discriminant Analysis ◽

Image Data ◽

Atmospheric Conditions ◽

Very High Frequency ◽

Vhf Radar ◽

Linear Discriminant ◽

Radar Echoes ◽

Summer Echoes ◽

Percent Accuracy

Polar Mesospheric Summer Echoes (PMSE) are distinct radar echoes from the Earth’s upper atmosphere between 80 to 90 km altitude that form in layers typically extending only a few km in altitude and often with a wavy structure. The structure is linked to the formation process, which at present is not yet fully understood. Image analysis of PMSE data can help carry out systematic studies to characterize PMSE during different ionospheric and atmospheric conditions. In this paper, we analyze PMSE observations recorded using the European Incoherent SCATter (EISCAT) Very High Frequency (VHF) radar. The collected data comprises of 18 observations from different days. In our analysis, the image data is divided into regions of a fixed size and grouped into three categories: PMSE, ionosphere, and noise. We use statistical features from the image regions and employ Linear Discriminant Analysis (LDA) for classification. Our results suggest that PMSE regions can be distinguished from ionosphere and noise with around 98 percent accuracy.

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Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity

Annales Geophysicae ◽

10.5194/angeo-27-1909-2009 ◽

2009 ◽

Vol 27 (5) ◽

pp. 1909-1914 ◽

Cited By ~ 4

Author(s):

A. Yoshida

Keyword(s):

Solar Wind ◽

Wind Velocity ◽

Geomagnetic Activity ◽

Physical Meaning ◽

Solar Wind Velocity ◽

Annual Variation ◽

Geomagnetic Disturbance ◽

Data Sets ◽

Key Factor ◽

Solar Wind Parameters

Abstract. Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity is investigated based on the three-hourly am index and solar wind parameters. When the z component of the interplanetary magnetic field (IMF) in geocentric solar magnetospheric (GSM) coordinates is southward, am indices are well correlated with BsVx2, where Bs is the southward component of the IMF and Vx is the solar wind velocity in the sun-earth direction. The am-BsVx2 relationship, however, depends on the range of Vx2: the am in higher ranges of Vx2 tends to be larger than am in lower ranges of Vx2 for the same value of BsVx2 for both equinoctial and solstitial epochs. Using the data sets of the same Vx2 range, it is shown that distribution of points in the am-BsVx2 diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each BsVx2 bin in solstitial epochs are closely consistent with those in equinoctial epochs, if Vx2 for each point at solstices are reduced to Vx2sin2 (Ψ) where Ψ is the geomagnetic colatitude of the sub-solar point. Further, it is shown that monthly averages of the am index in the long period is well correlated with the values of sin2(ψ) for the middle day of each month. These findings indicate that the factor that contributes to the generation of geomagnetic disturbance is not the velocity of the solar wind, but the component of the solar wind velocity perpendicular to the dipole axis of the geomagnetic field. The magnitude of the perpendicular velocity component varies semi-annually even if the solar wind velocity remains constant, which is considered to be the long-missed key factor causing the equinoctial effect.

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Radar efficiency and the calculation of decade-long PMSE backscatter cross-section for the Resolute Bay VHF radar

Annales Geophysicae ◽

10.5194/angeo-27-1643-2009 ◽

2009 ◽

Vol 27 (4) ◽

pp. 1643-1656 ◽

Cited By ~ 12

Author(s):

N. Swarnalingam ◽

W. K. Hocking ◽

P. S. Argall

Keyword(s):

Cross Section ◽

Great Level ◽

Vhf Radar ◽

Radar Echoes ◽

Summer Echoes ◽

Resolute Bay ◽

Absolute Measurements ◽

Coherent Radar ◽

Backscatter Cross Section

Abstract. The Resolute Bay VHF radar, located in Nunavut, Canada (75.0° N, 95.0° W) and operating at 51.5 MHz, has been used to investigate Polar Mesosphere Summer Echoes (PMSE) since 1997. PMSE are a unique form of strong coherent radar echoes, and their understanding has been a challenge to the scientific community since their discovery more than three decades ago. While other high latitude radars have recorded strong levels of PMSE activities, the Resolute Bay radar has observed relatively lower levels of PMSE strengths. In order to derive absolute measurements of PMSE strength at this site, a technique is developed to determine the radar efficiency using cosmic (sky) noise variations along with the help of a calibrated noise source. VHF radars are only rarely calibrated, but determination of efficiency is even less common. Here we emphasize the importance of efficiency for determination of cross-section measurements. The significant advantage of this method is that it can be directly applied to any MST radar system anywhere in the world as long as the sky noise variations are known. The radar efficiencies for two on-site radars at Resolute Bay are determined. PMSE backscatter cross-section is estimated, and decade-long PMSE strength variations at this location are investigated. It was noticed that the median of the backscatter cross-section distribution remains relatively unchanged, but over the years a great level of variability occurs in the high power tail of the distribution.

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Influence of tides and gravity waves on layering processes in the polar summer mesopause region

Annales Geophysicae ◽

10.5194/angeo-26-4013-2008 ◽

2008 ◽

Vol 26 (12) ◽

pp. 4013-4022 ◽

Cited By ~ 21

Author(s):

P. Hoffmann ◽

M. Rapp ◽

J. Fiedler ◽

R. Latteck

Keyword(s):

Gravity Waves ◽

Lower Layer ◽

Vhf Radar ◽

Remarkable Feature ◽

Ice Cloud ◽

Radar Echoes ◽

Layer Structures ◽

Short Period ◽

Summer Echoes ◽

Polar Mesosphere Summer Echoes

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.

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Characteristics of layered occurrence ratio of polar mesosphere summer echoes observed by EISCAT VHF 224 MHz Radar

10.5194/angeo-2019-13 ◽

2019 ◽

Author(s):

Shucan Ge ◽

Hailong Li ◽

Tong Xu ◽

Mengyan Zhu ◽

Maoyan Wang ◽

...

Keyword(s):

Very High Frequency ◽

Vhf Radar ◽

Seasonal Behavior ◽

Incoherent Scatter ◽

K Index ◽

Radar Echoes ◽

Threshold Conditions ◽

Summer Echoes ◽

Polar Mesosphere Summer Echoes ◽

Density Threshold

Abstract. Polar Mesosphere Summer Echoes (PMSE) are strong radar echoes observed in polar mesopause during local summer. Measurements of layered PMSE observed by the European Incoherent Scatter Scientific Association Very high frequency (EISCAT VHF) radar from 2004 to 2015 in the latest solar cycle, can be used to study the variations of PMSE occurrence ratio (OR). The seasonal variation of PMSE mono-, double- and tri-layer occurrence ratio was analyzed, and there is different seasonal behavior. A method was given to calculate the PMSE mono-, double- and tri-layer occurrence ratio under different electron density threshold conditions. In addition, the correlation between PMSE layered occurrence ratios and solar 10.7 cm flux index (F10.7), and the correlation between PMSE layered occurrence ratios and geomagnetic K index were analyzed respectively in this study. It can be obtained that PMSE mono-, double- and tri-layer OR are positively correlated with the K index. The correlation coefficient between PMSE mono- and double-layer OR and F10.7 is weak, and the PMSE tri-layer OR has a negative correlation with F10.7.

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Characteristics of the layered polar mesosphere summer echoes occurrence ratio observed by EISCAT VHF 224 MHz radar

Annales Geophysicae ◽

10.5194/angeo-37-417-2019 ◽

2019 ◽

Vol 37 (3) ◽

pp. 417-427

Author(s):

Shucan Ge ◽

Hailong Li ◽

Tong Xu ◽

Mengyan Zhu ◽

Maoyan Wang ◽

...

Keyword(s):

Very High Frequency ◽

Vhf Radar ◽

Seasonal Behavior ◽

Incoherent Scatter ◽

K Index ◽

Radar Echoes ◽

Summer Echoes ◽

Polar Mesosphere Summer Echoes ◽

Geomagnetic Activities ◽

Density Threshold

Abstract. Polar mesosphere summer echoes (PMSEs) are strong radar echoes observed in the polar mesopause during the local summer. Observations of layered PMSEs carried out by the European Incoherent Scatter Scientific Association very-high-frequency (EISCAT VHF) radar during 2004–2015 in the latest solar cycle are used to study the variations of the PMSE occurrence ratio (OR). Different seasonal behavior of PMSEs is found by analyzing the seasonal variation of PMSE mono-, double-, and tri-layer OR. A method was used to calculate the PMSE mono, double-, and tri-layer OR under a different electron density threshold. In addition, a method to analyze the correlation of the layered PMSE OR with the solar 10.7 cm flux index (F10.7) and geomagnetic K index is proposed. Based on it, the correlation of the layered PMSE OR with solar and geomagnetic activities is not expected to be affected by discontinuous PMSEs. It is found that PMSE mono-, double-, and tri-layer ORs are positively correlated with the K index. The correlation of the PMSE mono- and double-layer OR with F10.7 is weak, whereas the PMSE tri-layer OR shows a negative correlation with F10.7.

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Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: the importance of nitric oxide

Annales Geophysicae ◽

10.5194/angeo-31-333-2013 ◽

2013 ◽

Vol 31 (2) ◽

pp. 333-347 ◽

Cited By ~ 8

Author(s):

S. Kirkwood ◽

E. Belova ◽

P. Dalin ◽

M. Mihalikova ◽

D. Mikhaylova ◽

...

Keyword(s):

Nitric Oxide ◽

Lognormal Distribution ◽

Geomagnetic Disturbance ◽

Auroral Zone ◽

Local Times ◽

Delayed Response ◽

Magnetic Disturbance ◽

Geomagnetic Disturbances ◽

Summer Echoes ◽

Polar Mesosphere Summer Echoes

Abstract. The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic K indices) is examined. Calibrated PMSE reflectivities for the period May 2006–February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68° N, geomagnetic latitude 65°) and at two different sites in Queen Maud Land, Antarctica (73°/72° S, geomagnetic latitudes 62°/63°). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and K indices) and low correlations for minute-to-day timescales.

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D region observations by VHF and HF radars to investigate Polar Mesospheric Winter Echoes

10.5194/egusphere-egu21-14463 ◽

2021 ◽

Author(s):

Toralf Renkwitz ◽

Ralph Latteck ◽

Irina Strelnikova ◽

Jorge L. Chau ◽

Boris Strelnikov

Keyword(s):

Solar Minimum ◽

Spectral Width ◽

Hf Radar ◽

Geomagnetic Disturbances ◽

Statistical Parameters ◽

Vhf Radar ◽

Simultaneous Measurements ◽

Radar Echoes ◽

D Region ◽

Underlying Processes

<p>Polar Mesospheric Winter Echoes (PMWE) have been observed by VHF radars for quite some years. Until now, most of the studies were focussed on either major events, that occurred during solar and geomagnetic severely distorted conditions or statistical parameters like their seasonal and interannual occurrence rates as well as altitude distributions were investigated. However, especially the origin of PMWE and underlying processes are still under debate and further observations aim to contribute to this question. Recent PMWE observations with the MAARSY VHF radar included experiments using multiple beam directions to investigate the spatial structure and evolution of PMWE. Within this study we present results of MAARSY radar observations of PMWE layers complemented by simultaneous measurements by the Saura HF radar, located less than 20km apart. Major products of the Saura radar are horizontal winds and electron density within the D region. These parameters are important for both the formation and visibility of PMWE. The spectral width and localization of VHF and HF radar echoes for the presence of PMWE are analyzed and compared in the context of turbulence. Furthermore, observations during the solar minimum for the season 2019/2020 appear to be a suitable period to deepen the investigation of background conditions, excluding intensive geomagnetic disturbances.</p>

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Evaluation of the Power Transformer Magnetizing Inrush Currents

Elektrichestvo ◽

10.24160/0013-5380-2020-10-20-32 ◽

2020 ◽

Vol 10 (10) ◽

pp. 20-32

Author(s):

Aleksey A. KUVSHINOV ◽

◽

Vera V. VAKHNINA ◽

Aleksey N. CHERNENKO ◽

◽

...

Keyword(s):

Power Transformer ◽

Geomagnetic Disturbance ◽

Inrush Current ◽

Geomagnetic Disturbances ◽

Disturbance Intensity ◽

Magnetizing Inrush Current ◽

Inrush Currents ◽

Instantaneous Values ◽

The Mathematical Model ◽

Analytical Expressions

The mathematical model of a shell-core power transformer’s magnetization branch is substantiated. By using the model, analytical expressions for the magnetizing current instantaneous values under the conditions of geomagnetic disturbances can be obtained. Quantitative assessments of the magnetizing inrush current amplitudes and durations versus the geomagnetic disturbance intensity are obtained. The dynamics of the power transformer magnetic system saturation transient and changes in the magnetization inrush current amplitudes and durations after a sudden occurrence of geomagnetic disturbances are shown. The error of estimating the magnetizing inrush current amplitudes under geomagnetic disturbances is determined based on comparison with experimental data.

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