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Silicate dust is found in a wide range of astrophysical environments. Nucleation and growth of silicate dust grains in circumstellar environments likely involves species with diameters ranging from <1 nm (molecular silicates) to a few nanometers (nanosilicates). When fully formed silicate grains with sizes ∼0.1 μm enter the interstellar medium, supernovae shockwaves cause collision-induced shattering which is predicted to redistribute a significant proportion of the silicate dust mass into a huge number of nanosilicates. This presumed population has thus far not been unambiguously confirmed by observation but is one of the main candidates for causing the anomalous microwave emission. By virtue of their extreme small size, nanosilicates and molecular silicates could exhibit significantly different properties to larger silicate grains, which could be of astrochemical and astrophysical importance. Herein, we briefly review the properties of these ultrasmall silicate dust species with a focus on insights arising from bottom-up atomistic computational modelling. Finally, we highlight how such modelling also has the unique potential to predict observationally verifiable spectral features of nanosilicates that may be detectable using the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

We consider the M1.1-class solar flare occurred on July 5, 2012, at UT. This event is unique in that a helioseismic perturbation was detected in it despite its low hard X-ray flux in the 25–50 keV energy band and its very soft hard X-ray spectrum. As a rule, most of the known sunquakes have been detected in solar flares with large hard X-ray fluxes at high energies (at least up to 100–300 keV). The event under consideration contradicts the popular hypothesis about the generation of sunquakes by beams of accelerated high-energy electrons. An analysis of the available RHESSI X-ray spectra shows that they can be explained in two ways. The X-ray spectrum in the 25–50 keV energy band is explained by a power-law distribution of accelerated electrons with an power-law index of 7–9 or by the presence of a superhot plasma with a temperature –60 MK. In both cases, we are dealing with electrons of relatively low energies that either were responsible for the sunquake generation or should be considered as a secondary (accompanying) phenomenon with respect to the true cause of the photospheric perturbation. The results of a joint analysis of the X-ray and microwave spectra are presented for the first time for a helioseismically active solar flare. Our analysis shows that the spectra in both ranges can be well explained by the emission of a superhot magnetized plasma and not by accelerated electrons with a soft spectrum. However, the explanation of the spectra when considering partially magnetically trapped accelerated electrons is also possible. We have estimated the parameters of the thermal plasma, accelerated electrons, and energy fluxes of various types. We analyze the dynamics of ultraviolet and X-ray emission sources. We also present an analysis of the magnetic field structure based on vector magnetograms and the nonlinear force-free coronal magnetic field extrapolation. We discuss the mechanisms for the generation of the helioseismic perturbation during the solar flare under consideration. An eruptive process could probably be both primary and secondary causes of the sunquake. The appearance of a superhot plasma in the corona could give rise to propagating thermal fronts into the lower layers of the solar atmosphere, where helioseismic waves are excited. Our analysis does not allow the possibility of the sunquake generation by accelerated electrons with a soft spectrum to be ruled out either. [ABSTRACT FROM AUTHOR]

Numerous jets were observed in the extreme ultraviolet images of the SDO/AIA space observatory in early March 2015 in the developing active region of a complex magnetic configuration located near the eastern limb of the Sun. The analysis of the observations of several jets showed that the place of their origin and the direction of motion of the material was such that it absorbed the radiation of the regions of the quiet Sun with an area of less than 1% of the area of the solar disk. There was also a partial screening of the flare radio source located to the north of the stationary one. Only in one case, the appearance of jet led to a response in the microwave range in the form of a small depression of radio emissions (negative burst), registered on the records of the Nobeyama radio polarimeters and the Ussuriysk radiometer. Distinguishing features of this event from other jets are revealed. Simultaneously with the studied jet, whose material moved to the east of the active region, small jets were observed to the northwest of it. This led to an increase in the total screening area of the quiet Sun regions, which exceeded 1% of the area of the solar disk. Another jet arose immediately before the jet, as a result of which the material returned to the solar surface probably had a large mass compared to other jets, which manifested itself in the maximum absorption value compared to other cases. The radio burst before the depression of radio emissions was impulsive and there was no activity in other regions of the Sun. The combination of these factors was the cause of the negative burst of small depth. In other cases, the possible depression of radio emissions could be compensated by an increased level of radio emissions due to additional activity, or the mass of the jet material was insufficient for the occurrence of negative bursts. [ABSTRACT FROM AUTHOR]

In passive microwave remote sensing of the Earth's surface, it is essential to relate the emission to geophysical parameters. The emissivity ranges between 0 and 1. Hence, a slight emissivity variation leads to a significant change in brightness temperature. Many sources of error contribute to such tiny variations in emission. This paper quantifies microwave emission variability from a rough surface through model simulation due to the non-Gaussianity in height probability density (HPD) and power spectrum density (PSD). We considered Gaussian and exponential distributions for surface height and correlation functions, representing two extremes of asperity and skewness. Additionally, the surface under consideration contains multiscale roughness. The impact of the HPD and multiscale roughness on the polarization index of the emissivity is evaluated as a function of frequency and roughness. In general, assuming that Gaussian-distributed height leads to an underestimation of the emissivity, with V polarization being less sensitive to the non-Gaussian HPD and PSD effects than H polarization, the emissions are enhanced at high roughness with small look angles but are reduced for smooth surfaces at large look angles under non-Gaussian PSD. In a specific scenario, the dynamic range of the difference between exponential and Gaussian HPD is 0~10%, and the difference in emissivity caused by non-Gaussian PSD ranges from −2% to 16%. These results should be helpful in interpreting the radiometric measurements that exhibit fluctuations and differences with model predictions. [ABSTRACT FROM AUTHOR]

Radio continuum, microwave and gamma-ray images of the Milky Way reveal a conspicuous, loop-like structure that fills almost half of the northern Galactic hemisphere, called Loop I. The interior of Loop I is the most conspicuous region shining in soft X-rays, whose eastern base is a remarkably bright, elongated structure seeming to emerge from the Galactic plane, dubbed the North Polar Spur (NPS). After 40 years of debates, two very different, contradictory views of Loop I/NPS are still defended: on the one hand, the NPS is a gigantic volume of expanding hot gas that envelops and extends the northern “Fermi Bubble” (FB) known to be blown by the Galactic center, and Loop I marks the shock front; on the other hand, the NPS is totally independent of the northern FB, it is a nearby, ordinary cavity of hot gas blown by supernovae, Loop I is its shock front and both are coincidentally located in the direction of the FB. To an observer at the Sun, both can produce the same perspective view, although the former has a size comparable to the Milky Way itself, and the latter a diameter of a few hundreds parsecs. The energy involved varies by 3-4 orders of magnitude, and the solution has important consequences on the structure and history of our Galactic neighborhood, on the age of the North and South FBs and the activity at the Galactic center. Moreover, whatever are the actual shape and distance of Loop I/NPS, accurate modeling of the polarized emission associated with Loop I is important for CMB foreground removal. After a short review, I discuss recent results which have a connection with Loop I/NPS. Some of them have been used as arguments in the two opposite ways, while for others the connections with LoopI/NPS have been overlooked. They involve very different spacecraft, from a 12 Kg Cubesat (HaloSat) to major space-borne observatories (HST, Gaia, and Spektr-RG). I make use of updated 3D maps of dust and a recent massive star catalog. I distinguish arguments based on geometric similarity or dissimilarity from those derived from measurements and physical models. Considering all past and recent constraints, it is clear that there is no entirely local or entirely distant scenario that is free from contradictions with some of the data analyses or from improbable coincidences. I discuss a speculative scenario, partially inspired by recent BF and Milky Way gas models, combining near and far aspects and seeming to be able to meet the various constraints. However, new data and models are needed to bring the controversy to a close and we can still expect new episodes of this long story.

Natural rough surfaces have inherent multiscale roughness. This article presents the modeling and analysis of microwave emission from a multiscale soil surface. Unlike the linear superposition of different correlation functions with various correlation lengths, we applied the frequency modulation concept to characterize the multiscale roughness, in which the modulation does not destroy the surface's curvature but only modifies it. The multiscale effect on emission under different observation geometries and surface parameters was examined using an AIEM model. The paper provides new insights into the dependence of polarized emissivity on multiscale roughness: V-polarized emissivity is much less sensitive to multiscale roughness across the moisture content from dry to wet (5–30%). The H-polarized is sensitive to multiscale roughness, especially at higher moisture content. The predicted emissivity will have considerable uncertainty, even for the same baseline correlation length, without accounting for the multiscale roughness effect. V-polarized emissivity is less sensitive to the multiscale effect than H-polarized and the higher modulation ratio indicates larger emissivity. The higher modulation ratio indicates larger emissivity. Multiscale roughness weakens the polarization difference, particularly in higher moisture conditions. In addition, ignoring the multiscale effect leads to underestimated emissivity to a certain extent, particularly at the larger RMS height region. Finally, when accounting for multiscale roughness, model predictions of emission from a soil surface are in good agreement with two independently measured data sets. [ABSTRACT FROM AUTHOR]

We analyze the presence of a microwave neutral-line-associated source (NLS) in a super-active region NOAA 12673, which produced a number of geo-effective events in September 2017. To estimate the NLS position, we use data from the Siberian Radioheliograph in a range 4–8 GHz and from the Nobeyama Radioheliograph at 17 GHz. Calculation of the coronal magnetic field in a non-linear force-free approximation has revealed an extended structure consisting of interconnected magnetic flux ropes, located practically along the entire length of the main polarity separation line of the photospheric magnetic field. NLS is projected into the region of the strongest horizontal magnetic field, where the main energy of this structure is concentrated. During each X-class flare, the active region lost magnetic helicity and became a CME source.

Good understanding the emission in the presence of foam layer is essential for effective retrieval of oceanic parameter from microwave measurements. In general, microwave emissivity is enhanced by the foam layer, depending not only on the macroscopic dielectric properties and the foam layer thickness, but also on the absorption and scattering of the bubbles. In this paper, a numerical emission model is developed based on a matrix doubling method by which the volume scattering effects in foam layer are accounted for. We explore the effects of the water fraction and foam layer thickness on total emission from foam-covered ocean surface, by analyzing the contributions from both the up-welling and the down-welling emissions from foam layer, and the emission from the seawater. In particular, the dependence of emission, consisting of the three effective emission sources, on the foam layer thickness and water fraction at L-band to Ka-band are investigated. Results are compared with predictions by the incoherent method. Physical reasons given rise to the depolarized emissivity at high frequency bands, and the dry sub-layers at the top of foam layer are discussed.

This paper is a study of the spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) from two active regions NOAA 12673 and NOAA 11261 for several hours prior to powerful class M x-ray flares. The spatial distribution of the radio brightness and emission intensity in certain parts of the active region is found to be highly nonstationary. Data in the ultraviolet (AIA/SDO) are also used for studying the fine structure of the active emission sources. It is shown that the spatial dynamics of the microwave sources correlates well with the position and appearance of bright ultraviolet (UV) loops in the 94 Å line, i.e., with magnetic loops where the plasma is heated to high temperatures ~107 K. A combined analysis of the UV and radio emission charts with magnetic field charts (HMI/SDO) for NOAA 12673 shows that the highly nonstationary behavior of the microwave sources develops simultaneously with the ignition of a system of intersecting UV loops (X-structures). It is also shown that the bright UV loops and microwave sources arise in the area where new magnetic fluxes emerge. [ABSTRACT FROM AUTHOR]

This study monitored thermal denaturation of albumin using microwave radiometry. Brightness Temperature, derived from Microwave Emission (BTME) of an aqueous solution of bovine serum albumin (0.1 mM) was monitored in the microwave frequency range 3.8–4.2 GHz during denaturation of this protein at a temperature of 56°C in a conical polypropylene cuvette. This method does not require fluorescent or radioactive labels. A microwave emission change of 1.5–2°C in the BTME of aqueous albumin solution was found during its denaturation, without a corresponding change in the water temperature. Radio thermometry makes it possible to monitor protein denaturation kinetics, and the resulting rate constant for albumin denaturation was 0.2 ± 0.1 min−1, which corresponds well to rate constants obtained by other methods.

Abstract: This paper presents an analysis of the experimental measurements of the azimuthal anisotropy of the microwave emissions of a rough water surface. The experimental data were obtained using microwave radiometers with operating frequencies of ~37 GHz (a wavelength of ~8 mm) on the oceanographic platform of the Black Sea Hydrophysical Experimental Facility of the Russian Academy of Sciences in the period from 2005 to 2016. This paper describes the azimuthal anisotropy effect, experimental studies, measurement methods, and data processing. A qualitative comparison of the measurement results with the model calculations and other experimental studies of anisotropy was performed. It was shown that there is a strong sensitivity of the variation in the radio emissions of a rough water surface, both to the wind speed and to its direction at different incidence observation angles. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the functional dependence of the microwave emission of a rough water surface at a frequency of 37.5 GHz (wavelength of ~8 mm). The MiROSE model (Microwave Rough Ocean Surface Emission model) is based on the experimental studies of the own thermal radio emission of the water surface, which were carried out in 2005 and 2007 on the oceanographic platform of the Black Sea Hydrophysical Experimental Facility of the Russian Academy of Sciences. This paper demonstrates the steps of the simulation for selecting the optimal functions to describe the incident angle, wind, and temperature dependences of the increment of the own water surface emission. The following parameters can be calculated on the basis of the proposed model: the increment of the brightness temperature, radio-brightness contrast, and radio-brightness temperature for horizontal and vertical polarizations of the received emission. The model is applicable to water temperatures ranging from 12.5 to 25°C, wind speeds of 3-13 m/s, and incident angles of 30°-80° measured from the nadir. [ABSTRACT FROM AUTHOR]

The matrix doubling (MD) model is a numerical solution to the radiative transfer equation. It can achieve better accuracy in simulating microwave signals from vegetated terrain by considering multiple-scattering effects. However, it is difficult to apply the MD model to retrieving work due to its high complexity. This letter presents a case study performed on corn to demonstrate a multiangular (5°–65°), multiband (1.4/6.925/10.65 GHz) microwave emission model considering multiple-scattering effects by parameterizing the MD model. The simulated emissivity differences between the theoretical model and parameterized model are small. The mean absolute percent errors are all less than 1%, and the root mean square errors (RMSEs) are all within the range of $10^{-3}$. Validations using airborne polarimetric L-band microwave radiometer data and ground-based trunk-mounted multifrequency microwave radiometer data indicate that the parameterized model achieves good accuracy with overall RMSEs within 8K at all three bands. [ABSTRACT FROM AUTHOR]

This study monitored thermal denaturation of albumin using microwave radiometry. Brightness Temperature, derived from Microwave Emission (BTME) of an aqueous solution of bovine serum albumin (0.1 mM) was monitored in the microwave frequency range 3.8–4.2 GHz during denaturation of this protein at a temperature of 56°C in a conical polypropylene cuvette. This method does not require fluorescent or radioactive labels. A microwave emission change of 1.5–2°C in the BTME of aqueous albumin solution was found during its denaturation, without a corresponding change in the water temperature. Radio thermometry makes it possible to monitor protein denaturation kinetics, and the resulting rate constant for albumin denaturation was 0.2 ± 0.1 min−1, which corresponds well to rate constants obtained by other methods. [ABSTRACT FROM AUTHOR]

A correlation analysis of the model calculations and experimental measurements of wind-speed sensitivity of a rough sea-surface microwave emission at a frequency of 37.5 GHz are presented. The field data used in the research were collected over 3 years in the summer and autumn periods at the oceanographic platform of the Marine Hydrophysical Institute, Russian Academy of Sciences (RAS). A hypothesis about a significant correlation between the model calculations and experimentally measured sea-surface emission ability caused by wind forcing was formulated and tested to reveal this correlation. An evaluation of the discrepancy between the model and experimental data has been performed by an analysis of residuals. Our studies have shown that among the selected models not a single one adequately describes the experimental data. [ABSTRACT FROM AUTHOR]

In this study, two retrieval algorithms for estimating the water content of vegetation (VWC) in the range 0–8 kg/m2 from multifrequency microwave radiometric data have been implemented, with the purpose of contributing to the development of an all-weather VWC product for the satellite AMSR2 radiometer of the JAXA (Japan Aerospace Exploration Agency) GCOM-W mission. The first algorithm estimates VWC through a semi-empirical combination of the polarization index (PI) acquired at X and Ku bands, while the second one endeavors to improve the retrieval accuracy adding C-band data and using an artificial neural network (ANN) method. The sensitivity to vegetation biomass of multifrequency PIs at various frequencies, which was already pointed out in the previous literature, has been first further evaluated with the support of the well-known tau-omega solution of the radiative transfer model and experimental data. Two years of AMSR2 data collected on a wide portion of Africa, which includes a large variety of vegetation types and biomasses, have been considered for implementing and testing both algorithms. VWC reference data with the same temporal and spatial coverage of AMSR2, needed for validating the algorithm outputs, have been derived from SPOT4 normalized difference vegetation index (NDVI), downsampled to the AMSR2 ground resolution. The test results provided a correlation coefficient R > 0.88 with root mean square error (RMSE) < 1.4 kg/m 2 for the semi-empirical algorithm, and R = 0.98 with RMSE < 0.5 kg/m2 for ANN algorithm, thus demonstrating that, although both approaches are able to estimate VWC, the ANN algorithm is able to obtain better results. An independent validation of the two algorithms was then carried out on the entire Australian continent, considering 4 periods of 16 days each in different seasons of 2013. In this case, the algorithm outputs have been compared with VWC derived from MODIS 16 days averaged NDVI. The independent validation, as expected, showed slightly worst results, with R = 0.82 and RMSE around 1.5 kg/m2 for the semi-empirical algorithm, and R = 0.88 and RMSE around 0.86 kg/m2 for the ANN. This study demonstrated that microwave data from AMSR2 and polarization indices can be legitimately used to produce vegetation maps on a global scale by separating several levels of biomass, without any need of further information from other sensors. [ABSTRACT FROM PUBLISHER]

ABSTRACT The goal of this study was to apply the concept of passive microwave remote sensing to find the data set of microwave brightness temperatures of the dry soil surface as a function of actual salinity factors that influence the dielectric properties of the soil. From the agricultural point of view, salinity factor refers to the state of accumulation of the soluble salts in the soil. In many area, this factor limiting plant growth (such as sodium chloride). The measurements of the dielectric permittivity were conducted using shorted-circuited-waveguide technique at L-and C-band microwave frequencies (i.e. 1.4GHz and 5GHz, respectively). The dielectric properties of the salted soil samples were investigated at a thermodynamic temperature of 20.4 c . The results show that the frequency of 1.4GHz (L-band) is more effective frequency for study of the penetration depth of the soil surface. Also the vertical polarized microwave signals is preferred to study the variation of the emission characteristics of the dry soil with respect to the salinity by using the microwave radiometric remote sensing techniques especially at low microwave frequency.

A comparison between two algorithms for estimating soil moisture with microwave satellite data was carried out by using the datasets collected on the four Agricultural Research Service (ARS) watershed sites in the US from 2002 to 2009. These sites collectively represent a wide range of ground conditions and precipitation regimes (from natural to agricultural surfaces and from desert to humid regions) and provide long-term in-situ data. One of the algorithms is the artificial neural network-based algorithm developed by the Institute of Applied Physics of the National Research Council (IFAC-CNR) (HydroAlgo) and the second one is the Single Channel Algorithm (SCA) developed by USDA-ARS (US Department of Agriculture-Agricultural Research Service). Both algorithms are based on the same radiative transfer equations but are implemented very differently. Both made use of datasets provided by the Japanese Aerospace Exploration Agency (JAXA), within the framework of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) and Global Change Observation Mission–Water GCOM/AMSR-2 programs. Results demonstrated that both algorithms perform better than the mission specified accuracy, with Root Mean Square Error (RMSE) ≤0.06 m3/m3 and Bias

We study analytically the generation process of the first harmonics of the pure electron weakly oblique Bernstein modes. This mode can appear as a result of the rise and development of a corresponding instability in a solar active region. We assume that this wave mode is modified by the influence of pair Coulomb collisions and a weak large-scale sub-Dreicer electric field in the pre-flare chromosphere near the footpoints of a flare loop. To describe the pre-flare plasma we used the model of the solar atmosphere developed by Fontenla, Avrett, and Loeser ( Astrophys. J. 406, 319, ). We show that the generated first harmonic is close to the upper-hybrid frequency. This generation process begins at the very low threshold values of the sub-Dreicer electric field and well before the beginning of the preheating phase of a flare. We investigate the necessary conditions for the existence of non-damped first harmonics of oblique Bernstein waves with small amplitudes in the flare area. [ABSTRACT FROM AUTHOR]

It was shown that composite materials based on Pb(Zr1-xTix)O3 (PZT) ferroelectric particles, covered with graphene nanosheets, can be used for wireless detection of force applied to those composites. Ferroelectric materials with their enhanced piezoelectric and emission properties are used in this case as electron sources. During the mechanical loading of composites so called ferroelectric emission (FEE) appears in form of shot impulses of electrons. The short electron impulses generate the intensive microwave impulses that can be detected by means of antenna. This composite could be used as sensor for wireless measurement of machinery components response on applied stress in the locations where the connection with cables is restricted. [ABSTRACT FROM AUTHOR]

Forests play an important role in the global carbon cycle and have a potential impact on global climatic change. Monitoring forest biomass is of considerable importance in understanding the hydrological cycle. Because of the problem of dense forest cover, no reliable method with which to retrieve soil moisture in forest areas from the microwave emission signature has been established. All of these issues relate to the microwave emissivity and transmissivity characteristics of a forest. The microwave emission contribution received by a sensor above a forest canopy comes from both the soil surface and the vegetation layer. To analyze the relationship of forest biomass and forest emission and transmissivity, a high-order emission model, the matrix-doubling model, which consists of both soil and vegetation models, was developed and then validated for a young deciduous forest stand in a field experiment. To simulate the emissivity and transmissivity of a deciduous forest in the L and X bands using the matrix-doubling model, the parameters of components of deciduous trees when the leaf area index varies from 1 to 10 were generated by an L-system and a forest growth model. The emissivity and transmissivity of a forest and the relationships of these parameters to forest biomass are presented and analyzed in this paper. Emissivity in the L band when the leaf area index is less than 6 and at viewing angles less than 40°, and transmissivity in the L band are the most sensitive parameters in deciduous forest biomass estimation. [ABSTRACT FROM AUTHOR]