High-latitude Stations Research Articles

Geomagnetic Disturbances That Cause GICs: Investigating Their Interhemispheric Conjugacy and Control by IMF Orientation

AbstractNearly all studies of impulsive geomagnetic disturbances (GMDs, also known as magnetic perturbation events MPEs) that can produce dangerous geomagnetically induced currents (GICs) have used data from the northern hemisphere. In this study, we investigated GMD occurrences during the first 6 months of 2016 at four magnetically conjugate high latitude station pairs using data from the Greenland West Coast magnetometer chain and from Antarctic stations in the conjugate AAL‐PIP magnetometer chain. Events for statistical analysis and four case studies were selected from Greenland/AAL‐PIP data by detecting the presence of >6 nT/s derivatives of any component of the magnetic field at any of the station pairs. For case studies, these chains were supplemented by data from the BAS‐LPM chain in Antarctica as well as Pangnirtung and South Pole in order to extend longitudinal coverage to the west. Amplitude comparisons between hemispheres showed (a) a seasonal dependence (larger in the winter hemisphere), and (b) a dependence on the sign of the By component of the interplanetary magnetic field (IMF): GMDs were larger in the north (south) when IMF By was >0 (<0). A majority of events occurred nearly simultaneously (to within ±3 min) independent of the sign of By as long as |By| ≤ 2 |Bz|. As has been found in earlier studies, IMF Bz was <0 prior to most events. When IMF data from Geotail, Themis B, and/or Themis C in the near‐Earth solar wind were used to supplement the time‐shifted OMNI IMF data, the consistency of these IMF orientations was improved.

Investigation on the MLT tidal variability during September 2019 minor sudden stratospheric warming

Tidal variability in the mesosphere and lower thermosphere (MLT) during September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing ground-based meteor radar wind observations from the equatorial, extratropical, middle, and high latitude stations and global reanalysis dataset. The polar warming is found to move from the mesosphere to the stratosphere until the peak warming day (PWD) of the SSW. The diurnal and semidiurnal tides at individual observational sites do not exhibit any consistent response during the observational interval, but a notable and consistent variability in some specific zonal wavenumber components, i. e., DW1 (migrating diurnal tide), DE3 (nonmigrating eastward wavenumber 3 diurnal tide), and SW2 (migrating semidiurnal tide) is found in the global reanalysis dataset. Incidentally, the warming event occurs during Spring equinox when a dominant seasonal change in the tidal activities generally takes place and hence seasonal variability is also looked into while identifying the SSW impact during the observational interval. It is found that the seasonal broad changes in the DW1, DE3, and SW2 amplitudes can be explained by the variability in the tidal sources, i.e., water vapor, convective activity, ozone, etc during the observational period. However, the extracted short-term variability in the global tidal modes on removing seasonal trend reveals noticeable response in connection with the warming event. The deseasoned amplitude of the DW1 significantly enhances around the PWD at most of the present latitudes. The deseasoned DE3 amplitude responds significantly in the middle atmosphere at low latitudes during the warming phase. The deseasoned SW2 exhibit clear enhancement around the PWD at all the latitudes. However, the deseasoned tidal features do not seem to correlate well with that of the source species unlike the seasonal ones that imply involvement of complex processes during the warming event, seeking further future investigations in this regard.

On the use of empirical models for high-latitude ionosphere

Comparative analysis between a global ionospheric empirical model, NeQuick2, with a regional empirical model for high-latitudes, E-CHAIM, has been presented. Based on the calculation of F2-peak parameters from both models and comparing them with one solar cycle data from 18 high-latitude ionosonde stations, it has been shown that E-CHAIM's average improvement over NeQuick2 is less than 0.15–0.2 MHz in foF2 and less than 15–20 km in hmF2. Data from 7 out of 18 stations showed less than or equal to 0.1 MHz improvement in foF2 using E-CHAIM over NeQuick2 including 2 out of 3 stations located in the auroral latitudes. At the other end, data from 13 out of 18 high latitude stations showed less than or equal to 10 km improvement in hmF2 including all three stations located in auroral latitudes, in using E-CHAIM over NeQuick2.

Unusual Enhancement of Midlatitude Sporadic-E Layers in Response to a Minor Geomagnetic Storm

This study investigates the variations of middle and low latitude sporadic-E (Es) layers in response to a geomagnetic storm. Es layers are observed by five ionosondes located in the Eastern Asian sector. The critical frequencies of Es layers (foEs) at six stations increased in sequence from high latitude stations to low latitude stations after IMF/Bz turning southward. Lomb–Scargle analysis shows the amplification of semidiurnal oscillation amplitude in the vertical height of Es layers during geomagnetic disturbance. Modeling results of the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) show the enhancement of the wind field in the mesosphere and the lower thermosphere (MLT) region. Our study provides evidence that the enhanced wind field in the MLT region during the storm period could result in the enhancement of Es layers at middle and low latitude.

Correction to: Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

Correction to: Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

The refractive and diffractive contributions to GPS signal scintillation at high latitudes during the geomagnetic storm on 7–8 September 2017

Different indices have been used to reflect, or monitor the ionospheric scintillation, e.g. the detrended carrier phase,σφ,S4,the rate of change of the vertical total electron content index (vROTI), as well as the ionosphere‐free linear combination (IFLC) of two carrier phases. However, few studies have been performed to investigate the refractive and diffractive contributions to these indices, especially during geomagnetic storms. In this study, we analyze the high-resolution (50 Hz) phase and amplitude measurements from four high-latitude stations in Svalbard, Norway during the geomagnetic storm on 7–8 September 2017. Our results show that at high latitudes, the high-pass filter with a standard cutoff frequency of 0.1 Hz sometimes cannot effectively remove the refraction-driven phase variations, especially during the geomagnetic storm, leading to a remaining refraction contribution to the detrended carrier phase andσφwhen scintillation happens. In the meanwhile, asvROTI is sensitive to the TEC gradients, regardless of small- or large-scale ionospheric structures, both refraction and diffraction effects can cause visible fluctuations ofvROTI. For most of the scintillation events, the phase indices (including detrended carrier phase,σφ, andvROTI), IFLC,andS4show consistent fluctuations, indicating that diffraction usually occurs simultaneously with refraction during scintillation. One interesting feature is that although the IFLC andS4are thought to be both related to the diffraction effect, they do not always show simultaneous correspondence during scintillations. The IFLC is enhanced during the geomagnetic storm, while such a feature is not seen inS4. We suggest that the enhanced IFLC during the geomagnetic storm is caused by the increased high-frequency phase power, which should be related to the enhanced density of small-scale irregularities during storm periods.

Свойства короткопериодной возмущенности полного электронного содержания на средних и высоких широтах

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Features of short-period variability of total electron content at high and middle latitudes

The study presents the results of comparative analysis of features of a short-period (with periods of internal gravity waves) variability of total electron content (TEC) in the ionosphere at middle (Novosibirsk) and high (Norilsk) latitudes over a long period of time (2003–2020). The period analyzed makes it possible to estimate not only diurnal and seasonal variations in the variability, but also its changes within the solar activity cycle. The level of TEC variability is shown to experience pronounced seasonal variations with maxima in winter months. The difference between the level of variability in winter and summer is about two times for Novosibirsk and up to seven times for Norilsk. The variability features a distinct diurnal variation; however, the diurnal dependence at the mid- and high-latitude stations differs significantly. At high latitudes, the level of variability in the winter period strictly depends on solar activity. For the mid-latitude station, there is no clear dependence of variability level on solar activity; in the years of solar maximum, on the contrary, a slight decrease in the variability is observed. In summer, the level of variability at both middle and high latitudes remains practically unchanged and does not depend on solar activity. The main features in the dynamics of variability are shown to be similar at stations located at other longitudes, except for the East American sector. The result obtained suggests that the short-period TEC variability at high latitudes is primarily related to changes in solar activity, but regular variations in the variability at midlatitudes are probably not associated with heliophysical activity. The observed increase in the level of short-period variability in the winter mid-latitude ionosphere is assumed to be related to an increase in wave activity in the stratosphere.

Agricultural practice contributed more to changes in soybean yield than climate change from 1981 to 2010 in northeast China.

Although climate change and agricultural practices have non-negligible impacts on crop yields, their quantitative contributions to soybean yields remain unclear. First-order difference multiple regression was used to determine the respective contributions of climate change and agricultural practice to changes in soybean yields at station level from 1981 to 2010 in northeast China. From 1981 to 2010, the soybean yields at 87% of the stations were increasing with an average 41.18 kg ha year-1 change trend in northeast China. The individual impacts of climate change and agricultural practice on soybean yield were -0.33% to 0.58% year-1 and -3.3% to 7.89% year-1 , respectively. The sensitivity of the soybean yield to climatic factors was related to latitude, and yields at high-latitude stations were positively correlated with temperature but negatively correlated with accumulated sunshine hours. Climate change contributed -24% to 38% to the trend in soybean yield, and the temperature had the greatest effect of all the climatic factors. The contribution of agricultural practices was greater than that of climate change, counteracting the adverse effects of climate change and even affecting the direction of soybean yield changes. In adaptive decision making, priority should be given to management measures that have less impact on the environment, such as breeding new varieties adapted to specific latitudes, thus promoting the sustainable production of soybeans. © 2021 Society of Chemical Industry.

Behavior of electron density in the ionosphere over Norilsk during the period of declining solar activity

We report the results of approximation of electron density Ne array obtained with a digisonde at the high-latitude station Norilsk (69.40° N, 88.10° E) during years of declining solar activity (2003–2006). The calculations are made using the author's semi-empirical model with new coefficients calculated specifically for the station Norilsk. We obtain altitudinal changes of annual variations in daily Ne at heights of the ionospheric layer F1 (120–200 km). Approximation of experimental data describes Ne quite satisfactorily at these heights. Nevertheless, there are periods with quite pronounced deviations of model values from the experiment. The presence of significant geomagnetic disturbances during these periods is probably one of the reasons for such deviations.

Поведение электронной концентрации в ионосфере над Норильском в период спада солнечной активности

We report the results of approximation of electron density Ne array obtained with a digisonde at the high-latitude station Norilsk (69.40° N, 88.10° E) during years of declining solar activity (2003–2006). The calculations are made using the author's semi-empirical model with new coefficients calculated specifically for the station Norilsk. We obtain altitudinal changes of annual variations in daily Ne at heights of the ionospheric layer F1 (120–200 km). Approximation of experimental data describes Ne quite satisfactorily at these heights. Nevertheless, there are periods with quite pronounced deviations of model values from the experiment. The presence of significant geomagnetic disturbances during these periods is probably one of the reasons for such deviations.

Калибровка модели авроральной ионосферы AIM-E для расчета параметров регулярного E-слоя

The E-Region Auroral Ionosphere Model (AIM-E) was developed to determine the chemical composition and electron density in the auroral zone at E-layer heights (90–150 km). Solar and magnetic activity input parameters for AIM-E are the three-hour Ap index and the daily solar radio flux at a wavelength of 10.7 cm (index F10.7). In this paper, we compare AIM-E calculations of the electron density for the daytime with EUV radiation spectrum specified in two different ways: 1) the EUV spectrum theoretically calculated using the F10.7 index as an input parameter; 2) using TIMED satellite direct measurements of the EUV spectrum. We have corrected the EUVAC EUV radiation model to specify a photoionization source in AIM-E. Calculations of regular E-region critical frequencies show good agreement with the vertical sounding data from Russian high-latitude stations. Results we obtained make it possible to do a quick on-line assessment of the regular E layer, using the daily index F10.7 as an input parameter.

AIM-E auroral ionosphere model adjustment for the regular E layer

The E-Region Auroral Ionosphere Model (AIM-E) was developed to determine the chemical composition and electron density in the auroral zone at E-layer heights (90–150 km). Solar and magnetic activity input parameters for AIM-E are the three-hour Ap index and the daily solar radio flux at a wavelength of 10.7 cm (index F10.7). In this paper, we compare AIM-E calculations of the electron density for the daytime with EUV radiation spectrum specified in two different ways: 1) the EUV spectrum theoretically calculated using the F10.7 index as an input parameter; 2) using TIMED satellite direct measurements of the EUV spectrum. We have corrected the EUVAC EUV radiation model to specify a photoionization source in AIM-E. Calculations of regular E-region critical frequencies show good agreement with the vertical sounding data from Russian high-latitude stations. Results we obtained make it possible to do a quick on-line assessment of the regular E layer, using the daily index F10.7 as an input parameter.

Local K-index scales correction for the high-latitude magnetic stations

To assess the magnetic activity, various indices (numerical characteristics of the planetary and local disturbance of the Earth’s magnetic field) are used. Most widely used for various purposes are the planetary Kp-index and the local K-index, proposed by Bartels. The K-index characterizes the Earth’s magnetic field disturbance in a 3-hour interval (0–3, 3–6, etc. UTC) and is defined in a range from 0 to 9 by the amplitude of the horizontal component deviation from the quiet level. K = 0 indicates the absence of geomagnetic activity, and K = 9 corresponds to a strong geomagnetic storm. The lower limit of K = 9 is the amplitude of magnetic field horizontal component variation above which the K-index is assigned the maximum value of 9. This limit is selected individually for each station, depending on its geomagnetic latitude. The latest scales of the K-indices boundaries for the Russian Arctic stations were determined in the middle of the last century and have not been corrected since then. The significant discrepancy between the K-indices calculated using these scales and the planetary Kp-index shows that they had to be refined, and in some cases, they must be re-selected. The local indices lower boundaries (K = 9) for stations in the Arctic Russian sector were determined. K-indices lower boundaries were received for the strong magnetic storm according to the IAGA procedure. It is shown that for different magnetic field horizontal component variation values K-indices for different observation points practically coincide with the Kp-index. The lower value K = 9 dependence on the observation point geomagnetic latitude is presented. This relation can be used to obtain the lower boundary of K = 9 for any magnetic station. A table with local K-index scales for Russian Arctic magnetic stations has been compiled.

Similarities of the total electron content behavior during geomagnetic storms

The study of the behavior of the ionosphere during disturbances is traditionally an important task. One of the authors in the GA 2018 paper found two groups of similar magnetic storms in 2013 and discovered a similarity in the behavior of the critical frequencies foF2 according to the data from the Sodanküla high-latitude station in the northern hemisphere, but this similarity was reduced to a negative disturbance, which is also characteristic of a large number of dissimilar magnetic storms. Nevertheless, it seemed interesting whether such a similarity could be inherent in the behavior of the total electron content TEC of the ionosphere. The study was carried out using data from three stations Juliusruh, Tromso, Longyearbyen near the 15° N meridian. It turned out that this similarity is observed in the behavior of foF2 and TEC, which is confirmed by high correlation coefficients between these parameters both during months and periods of disturbances.

Secular change in atmospheric Ar∕N<sub>2</sub> and its implications for ocean heat uptake and Brewer–Dobson circulation

Abstract. Systematic measurements of the atmospheric Ar∕N2 ratio have been made at ground-based stations in Japan and Antarctica since 2012. Clear seasonal cycles of the Ar∕N2 ratio with summertime maxima were found at middle- to high-latitude stations, with seasonal amplitudes increasing with increasing latitude. Eight years of the observed Ar∕N2 ratio at Tsukuba (TKB) and Hateruma (HAT), Japan, showed interannual variations in phase with the observed variations in the global ocean heat content (OHC). We calculated secularly increasing trends of 0.75 ± 0.30 and 0.89 ± 0.60 per meg per year from the Ar∕N2 ratio observed at TKB and HAT, respectively, although these trend values are influenced by large interannual variations. In order to examine the possibility of the secular trend in the surface Ar∕N2 ratio being modified significantly by the gravitational separation in the stratosphere, two-dimensional model simulations were carried out by arbitrarily modifying the mass stream function in the model to simulate either a weakening or an enhancement of the Brewer–Dobson circulation (BDC). The secular trend of the Ar∕N2 ratio at TKB, corrected for gravitational separation under the assumption of weakening (enhancement) of BDC simulated by the 2-D model, was 0.60 ± 0.30 (0.88 ± 0.30) per meg per year. By using a conversion factor of 3.5 × 10−23 per meg per joule by assuming a one-box ocean with a temperature of 3.5 ∘C, average OHC increase rates of 17.1 ± 8.6 ZJ yr−1 and 25.1 ± 8.6 ZJ yr−1 for the period 2012–2019 were estimated from the corrected secular trends of the Ar∕N2 ratio for the weakened- and enhanced-BDC conditions, respectively. Both OHC increase rates from the uncorrected- and weakened-BDC secular trends of the Ar∕N2 ratio are consistent with 12.2 ± 1.2 ZJ yr−1 reported by ocean temperature measurements, while that from the enhanced-BDC is outside of the range of the uncertainties. Although the effect of the actual atmospheric circulation on the Ar∕N2 ratio is still unclear and longer-term observations are needed to reduce uncertainty of the secular trend of the surface Ar∕N2 ratio, the analytical results obtained in the present study imply that the surface Ar∕N2 ratio is an important tracer for detecting spatiotemporally integrated changes in OHC and BDC.

Land Surface Air Temperature Variations Across the Globe Updated to 2019: The CRUTEM5 Data Set

AbstractClimatic Research Unit temperature version 5 (CRUTEM5) is an extensive revision of our land surface air temperature data set. We have expanded the underlying compilation of monthly temperature records from 5,583 to 10,639 stations, of which those with sufficient data to be used in the gridded data set has grown from 4,842 to 7,983. Many station records have also been extended or replaced by series that have been homogenized by national meteorological and hydrological services. We have improved the identification of potential outliers in these data to better capture outliers during the reference period; to avoid classifying some real regional temperature extremes as outliers; and to reduce trends in outlier counts arising from climatic warming. Due to these updates, the gridded data set shows some regional increases in station density and regional changes in temperature anomalies. Nonetheless, the global‐mean timeseries of land air temperature is only slightly modified compared with previous versions and previous conclusions are not altered. The standard gridding algorithm and comprehensive error model are the same as for the previous version, but we have explored an alternative gridding algorithm that removes the under‐representation of high latitude stations. The alternative gridding increases estimated global‐mean land warming by about 0.1°C over the course of the whole record. The warming from 1861–1900 to the mean of the last 5 years is 1.6°C using the standard gridding (with a 95% confidence interval for errors on individual annual means of −0.11 to +0.10°C in recent years), while the alternative gridding gives a change of 1.7°C.

Assessment of improvement of the IRI model for foF2 variability over three latitudes in different hemispheres during low and high solar activities

This paper discusses the diurnal and seasonal variations of the F2 layer critical frequency (foF2) and the improvement of performance of the IRI-2016 model in predicting foF2 over three latitudes in different hemispheres during low and high solar activities. We extracted the foF2 data from six ionosonde stations which are Manila (14.7oN, 121.1oE), Yamagawa (31.2oN, 130.6oE), Yakutsk (62.0oN,129.6oE), Townsville (19.6oS, 146.8oE), Hobart (42.9oS, 147.3oE) and Terre Adelie (66.6oS, 140.0oE). The data of both low solar activity (LSA) period and high solar activity (HSA) periods were divided into three seasons as Northern Summer (May, June, July and August), Equinoxes (March, April, September and October) and Northern Winter (November, December, January and February). The present study showed that the IRI-2016 performance is strongly dependent on the solar activity, latitude, season, local time and hemisphere. For both hemispheres, the foF2 values at low latitude station are larger than those at middle latitude station, whereas the foF2 values at middle latitude station are larger than those at high latitude station. The agreement between IRI2016-modelled foF2 and foF2 measurements on all stations selected in the northern hemisphere is best for North Summer and worst for North Winter. For northern hemisphere, the values of relative deviations during both solar activities are largest in high latitudes and smallest in middle latitudes. As for southern hemisphere, the values of relative deviations during LSA are largest in middle latitudes and smallest in high latitudes, whereas the values of relative deviations during HSA are largest in low latitudes and smallest in high latitudes. It is thought that the relative deviations in the observed foF2 values are caused by solar activity that strongly alter chemical and electromagnetic processes in the ionosphere. These results are important for future improvements depending on solar activity and seasons in the IRI model for foF2 values over three latitudes in different hemispheres.

Climatology of the short-period (8-h and 6-h) tides observed by meteor radars at Tromsø and Svalbard

The paper presents climatology of the poorly known, particularly at high latitudes, short-period (8- and 6-h) tides observed by meteor radars at high latitudinal stations Tromsø (70°N, 19°E) and Svalbard (78°N, 16°E) based on 16 years (2003–2018) and 18 years (2001–2018) of measurements, respectively. The main focus of this study is to clarify the seasonal variability and vertical structure of the two tides observed at both sites. It is found that at the two not very distant high-latitude stations Tromsø and Svalbard both tides have not only different seasonal variability but also some distinction in the altitude structure as well. In general the short-period tides at both sites are vertically upward propagating waves but with seasonally depending vertical wavelength. The two tides at Tromsø and the 8-h one at Svalbard reveal some inter-annual variability with a period of quasi-2 years. An assessment of the solar heating as the main mechanism for the generation of the 8- and 6-h tides simulated by the model WACCM6 is presented as well. The results could be used as benchmarks for model simulations and for understanding better the forcing mechanisms of these short-period tides at high latitudes.