Results Of Ground-based Measurements Research Articles

The effects of the acoustic resonance induced in the atmosphere

After strong earthquakes and volcanic eruptions, geomagnetic oscillations with frequencies of 3.5–4.0 mHz have sometimes been observed. In this paper, we theoretically study the probable cause of these phenomena, which is related to the vertical acoustic resonance arising between the Earth’s surface and the thermosphere due to the propagation of the atmospheric wave corresponding to the acoustic branch generated by surface displacements. In the plane layered model of the atmosphere and ionosphere with inclined geomagnetic field, we analyze the propagation of two-dimensional (2D) harmonic acoustic wave. The height of the reflecting atmospheric layer corresponds to the region of sharp temperature change close to the thermosphere boundary ∼80–90 km. In this case, the calculated fundamental resonant frequency is close to the frequencies of the observed oscillations. The solution of this problem is used to calculate currents and electromagnetic perturbations in the atmosphere and ionosphere. The ionospheric E-layer is considered in the thin layer approximation. In this approximation, the formulas describing the geomagnetic perturbations (GMP) in the ionosphere and on the Earth’s surface are derived. The GMP spectrum contains a sharp maximum at the frequency corresponding to the acoustic resonance. According to the calculations, close to the resonance frequency, the spectral powers of GMPs on the ground can reach 5–30 nT2/Hz, which is consistent with the results of ground-based measurements.

Spatio-temporal air quality assessment in Tehran, Iran, during the COVID-19 lockdown periods

Based on ground-based and satellite-based data, spatio-temporal analyses of air quality in Tehran were carried out during the lockdown periods (February-April) in 2020 and 2021. We evaluated the differences in temporal emissions of six air pollutants (NO2, CO, SO2, O3, PM2.5, and PM10) at various time scales, including diurnal, monthly, and relative changes. The results of ground-based measurements indicated that for all pollutants except O3, the magnitude decreased in 2020 (11-42%) compared to the baseline period (2015-2021). As a result of eased restrictions and unfavorable meteorological conditions, the reduction in air pollutants was lower in 2021 (5-32%), and PM2.5 and PM10 levels increased (3.75 and 11.22%). Satellite-based concentrations (NO2, CO, SO2, and AOD) varied from −8 to 54% in 2020 and from −41 to 60% in 2021 compared to 2019 as the pre-lockdown year. Concerning AOD, the trend is consistent with dust events during March and April in our region.

Comparison of Data of OMI Long-Term Measurements of NO2 Contents in the Stratosphere and Troposphere with the Results of Ground-Based Measurements

Comparison of Data of OMI Long-Term Measurements of NO2 Contents in the Stratosphere and Troposphere with the Results of Ground-Based Measurements

Correlation of the Sentinel 1 Radar Data with Ground-Based Measurements of the Soil Temperature and Moisture

This study analyzes the correlation between the Sentinel 1 radar data in the C band and the soil temperature and moisture measured at seven ground-based stations in France and Germany for the period of 2014–2016. The results of ground-based measurements of the soil temperature and moisture are available on the International Soil Moisture Network website. It has been shown that there are both positive and negative correlations between the backscattering coefficient (BSC) and the soil temperature and moisture measured on the ground. According to our results, the correlation depends on the soil texture and surface roughness. For strongly correlated variables, the regression relationships of the BSC with the soil parameters have been obtained.

Visualizing spatial distribution of atmospheric nitrogen dioxide by means of hyperspectral imaging.

We have developed a method to monitor the slant column density of nitrogen dioxide in the lower troposphere using a compact hyperspectral camera with a high spectral resolution of 1nm at the full width half-maximum. Measurements of skylight spectra were conducted in wavelength regions of 460-490nm and 550-610nm to retrieve the slant column densities of nitrogen dioxide, in addition to water vapor and oxygen dimer. The results of ground-based measurements are shown for the cases of urban air pollution and aircraft emission near an airport runway.

Stratospheric ozone distribution features from the results of simultaneous ground-based microwave measurements in Nizhni Novgorod and Kyrgyzstan

Presented are the results of studying the ozone layer over Nizhni Novgorod and Central Asia using the ground-based millimeter wavelength range equipment. Carried out is the comparison of results of ground-based measurements with the EOS Aura MLS data. The difference in the ozone layer structure at stratospheric heights is revealed during the joint measurements at the mentioned points in November 2010. The analysis demonstrates that this difference is caused by the influence of the polar stratospheric vortex. Proceeding from the experience of similar researches, the conclusion is made on the necessity of organizing the permanent domestic network of the ground-based microwave monitoring of the ozone layer.

Long-term trends of variations in total ozone content according to data of ground-based (Tomsk: 56.48°N, 85.05°E) and satellite measurements

The paper compares the results of ground-based measurements of the total ozone (TO) content in Tomsk (56.48°N, 85.05°E) using the M-124 ozonometer, with satellite data obtained with the help of TOMS instruments. Different algorithms of TO retrieval from satellite data are considered. The TO trends over Tomsk, and at some northern hemisphere sites, for the period of 1979–2010 are analyzed. Based on the satellite and ground-based measurements for Tomsk, there is a negative linear trend of (−2.3 ± 0.1) DU per year for the period of 1979–1995 and a positive trend of (1.08 ± 0.1) DU per year for the period of 1996–2010.

The effect that coarse particles have on estimates of both optical and radiation characteristics of dust aerosol

Based on mathematical simulation, quantitative estimates of the effect that coarse dust particles have on the accuracy of retrieving the optical characteristics of aerosol have been obtained from the results of ground-based measurements of the spectral fluxes of both direct and scattered solar radiations. The results of verifying a retrieval algorithm (used at the AERONET ground-based network) based on special test models showed that the aerosol characteristics retrieved with this algorithm are unsuitable for calculating integral solar fluxes and for simulating space spectrometric IR measurements when the concentration of dust particles in the atmosphere exceeds their concentration in the well-known CONT model of continental aerosol by a factor of two or more.

Validating NO2 measurements in the vertical atmospheric column with the OMI instrument aboard the EOS Aura satellite against ground-based measurements at the Zvenigorod Scientific Station

Data on the NO2 content in the vertical column of the atmosphere obtained with the Ozone Monitoring Instrument (OMI) aboard the EOS Aura satellite (United States) in the period from October 2004 to October 2007 are compared with the results of ground-based measurements at the Zvenigorod Scientific Station (55.7° N, 36.8° E). The “unpolluted”; part of the total NO2 content in the atmospheric column, which mostly represents the stratosphere, and the NO2 contents in the vertical column of the troposphere, including the lower layer, which is subject to pollution, are included in the comparison. The correlation coefficient between the results of ground-based and satellite measurements of the “unpolluted” total NO2 content is ∼0.9. The content values measured with the OMI instrument are smaller than the results of ground-based measurements (on average, by (0.30 ± 0.03) × 1015 cm−2 or by (11 ± 1)%). Therms discrepancy between the satellite and ground-based data is 0.6 × 1015 cm−2. The NO2 content in the vertical column of the troposphere from the results of satellite measurements is, on average, (1.4 ± 0.5) × 1015 cm−2, (or about 35%) smaller than from the results of ground-based measurements, and the rms discrepancy between them is about 200%. The correlation coefficient between these data is ∼0.4. This considerable discrepancy is evidently caused by the strong spatial (horizontal) inhomogeneity and the temporal variability of the NO2 field during episodes of pollution, which leads to different (and often uncorrelated) estimates of the NO2 content in the lower troposphere due to different spatial resolutions of ground-based and satellite measurements.

Formation of a Polarization Jet during the Expansion Phase of a Substorm: Results of Ground-Based Measurements

The ground-based polarization jet measurements at the Yakutsk ionosphere station (L= 3.0) for the years 1989–1991 (110 events) are compared with variations of the AE-index and with parameters of the local magnetic activity. It is shown that polarization jet development in the near midnight sector can occur during a period of no longer than 10 min on the expansion phase of a substorm. The formation of the polarization jet is accompanied by a specific magnetic field variation corresponding in shape to a fast passage of the Harang Discontinuity above the station. Statistical data are given on ground level observations of the polarization jet, which are close to those measured from satellites. The mean delay (averaged over the full data bank) between the onset of a substorm with AE≥ 500 nT and the moment of the polarization jet appearance at L= 3.0 is equal to 0.5 h near midnight and to 1.0 – 1.5 h in the evening sector. Estimations show that the duration of the polarization jet formation when energetic ions are injected into the Harang Discontinuity region above the ground station can last for about 10 min, and during this time the Harang Discontinuity can be shifted to the west. This is in qualitative agreement with the described observations.

Venera 9 and 10: Thermal radiometry

New data about the top clouds of Venus were obtained during the radiometric experiment on-board the Venera 9 and Venera 10 orbiters. A diurnal component of the ir thermal radiation was determined for the latitude range −40, +50°. The brightness temperature of radiation referred to the normal was measured; it was 244°K at night and 239°K at the subsolar point for the 7- to 13-, 17- to 30-μm bands. Minimum temperatures correspond to the meridian of local time 16.00 h and are 232°K. There is also a zone of lower temperatures in the region of local time 7.5 h. Absolute temperatures were measured with an accuracy of −1.9° +1.2°. Thermal radiation has no distinct latitudinal dependence but has a day-night asymmetry, with the night radiation flux exceeding that on the day side by 17%. The limb-darkening law for thermal radiation is rather complicated, depending on the time of day. There are at least two states of the radiating cloud cover: day and night. The extinction coefficient is close to 0.24 km −1. The analysis shows that the source function of the medium is close to Planck's function. During the day the flux of thermal radiation is assumed to be weakened by an aerosol medium forming by photochemical processes. Comparison of experimental and calculated data yields a particle concentration in the radiating cloud cover of about 95 cm −3. Experimental data and the results of ground-based measurements were used to determine the radiometric albedo of Venus, 0.79 −0.01 +0.02.