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Surface melting on the Antarctic Ice Sheet has been monitored by satellite microwave radiometry for over 40 years. Despite this long perspective, our understanding of the microwave emission from wet snow is still limited, preventing the full exploitation of these observations to study supraglacial hydrology. Using the Snow Microwave Radiative Transfer (SMRT) model, this study investigates the sensitivity of microwave brightness temperature to snow liquid water content at frequencies from 1.4 to 37 GHz. We first determine the snowpack properties for eight selected coastal sites by retrieving profiles of density, grain size and ice layers from microwave observations when the snowpack is dry during wintertime. Second, a series of brightness temperature simulations is run with added water. The results show that (i) a small quantity of liquid water (≈0.5 kgm-2) can be detected, but the actual quantity cannot be retrieved out of the full range of possible water quantities; (ii) the detection of a buried wet layer is possible up to a maximum depth of 1 to 6 m depending on the frequency (6–37 GHz) and on the snow properties (grain size, density) at each site; (iii) surface ponds and water-saturated areas may prevent melt detection, but the current coverage of these waterbodies in the large satellite field of view is presently too small in Antarctica to have noticeable effects; and (iv) at 1.4 GHz , while the simulations are less reliable, we found a weaker sensitivity to liquid water and the maximal depth of detection is relatively shallow (<10 m) compared to the typical radiation penetration depth in dry firn (≈1000 m) at this low frequency. These numerical results pave the way for the development of improved multi-frequency algorithms to detect melt intensity and the depth of liquid water below the surface in the Antarctic snowpack. [ABSTRACT FROM AUTHOR]

Melt occurrence in Antarctica is derived from L-band observations from the Soil Moisture and Ocean Salinity (SMOS) satellite between the austral summer 2010–2011 and 2017–2018. The detection algorithm is adapted from a threshold method previously developed for 19 GHz passive microwave measurements from the special sensor microwave imager (SSM/I) and special sensor microwave imager sounder (SSMIS). The comparison of daily melt occurrence retrieved from 1.4 and 19 GHz observations shows an overall close agreement, but a lag of few days is usually observed by SMOS at the beginning of the melt season. To understand the difference, a theoretical analysis is performed using a microwave emission radiative transfer model. It shows that the sensitivity of 1.4 GHz signal to liquid water is significantly weaker than at 19 GHz if the water is only present in the uppermost tens of centimetres of the snowpack. Conversely, 1.4 GHz measurements are sensitive to water when spread over at least 1 m and when present in depths up to hundreds of metres. This is explained by the large penetration depth in dry snow and by the long wavelength (21 cm). We conclude that SMOS and higher-frequency radiometers provide interesting complementary information on melt occurrence and on the location of the water in the snowpack. [ABSTRACT FROM AUTHOR]

The SMOS brightness temperature (T B ) collected on the East Antarctic Plateau revealed spatial signatures at L-band that have never before been observed when only higher-frequency passive microwave observations were available, and this has opened up a new field of research. Because of the much greater penetration depth, modeling the microwave ice sheet emission requires taking into account not only snow conditions on the surface, but should also include glaciological information. Even if the penetration depth of the L-band is not well known due to the uncertainty on the imaginary part of the ice permittivity, it is likely to be of the order of several hundreds of meters, which means that the temperature of the ice over a depth of nearly 1000 m influences the emission. Over such a depth, the temperature is related to both the surface conditions and to the ice sheet thickness, which in turn depends on the bedrock topography and on other glaciological variables. The present paper aims to provide a thorough theoretical explanation of the observed T B spatial variation close to the Brewster angle at vertical polarization, in order to limit the effect of surface and vertical density variability in the firn. In order to provide reliable inputs to the microwave emission models used for simulating T B data, an in-depth analysis of the temperature profiles was performed by means of glaciological models. The comparison between simulated and observed data over three transects totalling 2000 km in East Antarctica pointed out that, whereas the emission models are capable of explaining the T B spatial variations of several kelvins (0.7 and 2.9 K), they are unable to predict its absolute value correctly. This study also shows that the main limiting factor in simulating low-frequency microwave data is the uncertainty in the currently available imaginary part of the ice permittivity. [ABSTRACT FROM AUTHOR]

This study explores the seasonal variations in snow grain size on the East Antarctic Plateau, where dry metamorphism occurs, by using microwave radiometer observations from 2000 to 2022. Local meteorological conditions and large-scale atmospheric phenomena have been considered in order to explain some peculiar changes in the snow grains. We find that the highest ice divide is the region with the largest grain size in the summer, mainly because the wind speed is low. Moreover, some extreme grain size values with respect to the average (over +3σ) were identified. In these cases, the ERA5 reanalysis revealed a high-pressure blocking close to the onsets of the summer increase in the grain size. It channels moisture intrusions from the mid-latitudes, through atmospheric rivers that cause major snowfall events over the plateau. If conditions of weak wind and low temperature occur during the following weeks, dry snow metamorphism is facilitated, leading to grain growth. This determines anomalous high maximums of the snow grain size at the end of summer. These phenomena confirm the importance of moisture intrusion events in East Antarctica and their impact on the physical properties of the ice sheet surface, with a co-occurrence of atmospheric rivers and seasonal changes in the grain size with a significance of over 95 %. [ABSTRACT FROM AUTHOR]

Two electromagnetic models were used to simulate snow emission at L-band from in situ measurements of snow properties collected at Dome C in Antarctica. Two different approaches were used: one based on the radiative transfer theory and the other on the wave approach. The soil moisture ocean salinity (SMOS) satellite observations performed at 1.4 GHz (21 cm) were used to check the validity of these models. Model results based on the wave approach were in good agreement with SMOS observations, particularly for incidence angles lower than 55°. Comparisons suggest that the wave approach is more suitable to simulate brightness temperature at L-band than the transfer radiative theory, because interference between the layers of the snowpack is better taken into account. The model based on the wave approach was then used to investigate several L-band characteristics at Dome C. The emission e-folding depth, i.e., 67% of the signal, was estimated at 250 m, and 99% of the signal emanated from the top 900 m. L-band brightness temperature is only slightly affected by seasonal variations in surface temperature, confirming the high temporal stability of snow emission at low frequency. Sensitivity tests showed that good knowledge of density variability in the snowpack is essential for accurate simulations in L-band. [ABSTRACT FROM PUBLISHER]

The surface-wind response to sea-surface temperature (SST) and SST meridional gradient is investigated in the Gulf of Guinea by using daily observations and re-analyses in the 2000-2009 decade, with a focus on boreal spring and summer months (May to August), where quasi-biweekly fluctuations in the position of the northern front of the equatorial cold tongue induce quasi-biweekly equatorial SST anomalies. Following a large-scale wind acceleration (deceleration), an equatorial SST cold (warm) anomaly is created within a few days. In order to explain the local atmospheric response to this SST anomaly, the two following mechanisms are invoked: first, a colder (warmer) ocean decreases (increases) the vertical stability in the marine atmospheric boundary layer, which favours a weaker (stronger) surface wind; and second, a negative (positive) anomaly of SST meridional gradient induces a positive (negative) anomaly of the sea-level-pressure meridional gradient, which decelerates (accelerates) the surface wind. The first mechanism has an immediate effect in the equatorial belt between 1°S and 1°N (and to a lesser extent between 3°S and 1°S), whereas the second takes 1 or 2 days to adjust and damps anomalous southeasterlies up to 800 hPa in the low troposphere between 7°S and 1°N, through reversed anomalies of meridional SST and pressure gradient. This negative feedback leads to weaker (stronger) winds in the southeastern tropical Atlantic, which forces the opposite phase of the oscillation within about 1 week. Around the Equator, where the amplitude of the oscillation is found to be maximal, both mechanisms combine to maximize the wind response to the front fluctuations. Between the Equator and the coast, a low-level secondary atmospheric circulation takes control of the surface-wind acceleration or deceleration around 3°N, which reduces the influence of the SST-front fluctuations. [ABSTRACT FROM AUTHOR]

The role of air-sea interaction in the boreal spring precipitation of the West African monsoon is explored through the wind variability in the Gulf of Guinea. Linear regressions are performed in May-June during the decade 2000-2009 to investigate the origin and effect of the surface wind strengthening north of the Equator. It appears that the equatorial sea-surface temperature cooling intensifies a surface-wind equatorial divergence/coastal convergence circulation, and generates a cross-equatorial pressure gradient, which both strengthen the southerlies north of the Equator. This increases subsidence above the ocean and convection in the northern Gulf of Guinea. In addition, an abrupt change is observed in the surface wind pattern in the eastern equatorial Atlantic (EEA) between April and July. To investigate the transition mechanisms, a reference date is defined as the date when the surface wind north of the Equator becomes and remains stronger than south of the Equator. Thus the maintenance of strong southerlies north of the Equator is linked to a coincident installation of a deep circulation on the whole troposphere and a northward shift of the low atmospheric local circulation. The resulting sharp seasonal transition coincides each year with a southeasterly wind burst, suggesting that the equatorial SST cooling plays a role in the precipitation along the African coast during boreal spring. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Within the framework of European Space Agency (ESA) activities, several campaigns were carried out in the last decade with the purpose of exploiting the capabilities of multifrequency synthetic aperture radar (SAR) data to retrieve snow information. This article presents the results obtained from the ESA SnowSAR airborne campaigns, carried out between 2011 and 2013 on boreal forest, tundra and alpine environments, selected as representative of different snow regimes. The aim of this study was to assess the capability of X- and Ku-bands SAR in retrieving the snow parameters, namely snow depth (SD) and snow water equivalent (SWE). The retrieval was based on machine learning (ML) techniques and, in particular, of artificial neural networks (ANNs). ANNs have been selected among other ML approaches since they are capable to offer a good compromise between retrieval accuracy and computational cost. Two approaches were evaluated, the first based on the experimental data (data driven) and the second based on data simulated by the dense medium radiative transfer (DMRT). The data driven algorithm was trained on half of the SnowSAR dataset and validated on the remaining half. The validation resulted in a correlation coefficient $R \simeq 0.77$ between estimated and target SD, a root-mean-square error (RMSE) $\simeq 13$ cm, and bias = 0.03 cm. ANN algorithms specific for each test site were also implemented, obtaining more accurate results, and the robustness of the data driven approach was evaluated over time and space. The algorithm trained with DMRT simulations and tested on the experimental dataset was able to estimate the target parameter (SWE in this case) with $R =0.74$ , RMSE = 34.8 mm, and bias = 1.8 mm. The model driven approach had the twofold advantage of reducing the amount of in situ data required for training the algorithm and of extending the algorithm exportability to other test sites. [ABSTRACT FROM AUTHOR]

Internal temperature is an essential parameter for understanding ice sheet dynamics. Glaciological models provide estimations of temperature profiles over Antarctica and few boreholes are also available, but, at present, no measurement exists at the scale of the whole continent. The analysis of passive L-band observations from the Soil Moisture and Ocean Salinity (SMOS) satellite shows that, thanks to the high penetration depth (i.e. up to 1500 m), it is possible to infer information on in depth glaciological properties of the ice sheet including temperature. In this study, the temperature profile is retrieved from SMOS observations using jointly glaciological and emission models. The developed methodology is valid in the inner part of Antarctica where the ice sheet is almost stable (i.e. its velocity is limited to 10 m yr−1). This analysis points out that in several cases, differences are observed between retrieved temperature profiles and those predicted by glaciological models. In particular, some geophysical parameters, namely the geothermal heat flux and the mean annual accumulation, need to be modified with respect to their prior values in order to simulate SMOS brightness temperatures. Results also clearly show that the reliability of the retrieved profile in depth decreases with increasing ice thickness due to the limited penetration of microwaves in the ice. The obtained results prove the capability of L band (1.4 GHz) passive microwave sensors for investigating the internal temperature of the ice-sheet. • Internal ice sheet temperature: a key parameter for the understanding of the ice sheet dynamics. • It is not measurable from space: available only from glaciological models or in the few boreholes. • A method to derive it by using ESA SMOS is proposed here. • Glaciological Model and Microwave emission model are used for the retrieval. • Ice sheet temperature profile maps are obtained. [ABSTRACT FROM AUTHOR]

Detailed angular ground-based L-band brightness temperature (TB) measurements over snow covered frozen soil in a prairie environment were used to parameterize and evaluate an electromagnetic model, the Wave Approach for LOw-frequency MIcrowave emission in Snow (WALOMIS), for seasonal snow. WALOMIS, initially developed for Antarctic applications, was extended with a soil interface model. A Gaussian noise on snow layer thickness was implemented to account for natural variability and thus improve the TB simulations compared to observations. The model performance was compared with two radiative transfer models, the Dense Media Radiative Transfer-Multi Layer incoherent model (DMRT-ML) and a version of the Microwave Emission Model for Layered Snowpacks (MEMLS) adapted specifically for use at L-band in the original one-layer configuration (LS-MEMLS-1L). Angular radiometer measurements (30°, 40°, 50°, and 60°) were acquired at six snow pits. The root-mean-square error (RMSE) between simulated and measured TB at vertical and horizontal polarizations were similar for the three models, with overall RMSE between 7.2 and 10.5 K. However, WALOMIS and DMRT-ML were able to better reproduce the observed TB at higher incidence angles (50° and 60°) and at horizontal polarization. The similar results obtained between WALOMIS and DMRT-ML suggests that the interference phenomena are weak in the case of shallow seasonal snow despite the presence of visible layers with thicknesses smaller than the wavelength, and the radiative transfer model can thus be used to compute L-band brightness temperature. [ABSTRACT FROM AUTHOR]

Surface melting is one of the primary drivers of ice shelf collapse in Antarctica and is expected to increase in the future as the global climate continues to warm because there is a statistically significant positive relationship between air temperature and melting. Enhanced surface melt will impact the mass balance of the Antarctic Ice Sheet (AIS) and, through dynamic feedbacks, induce changes in global mean sea level (GMSL). However, the current understanding of surface melt in Antarctica remains limited in terms of the uncertainties in quantifying surface melt and understanding the driving processes of surface melt in past, present and future contexts. Here, we construct a novel grid-cell-level spatially distributed positive degree-day (PDD) model, forced with 2 m air temperature reanalysis data and spatially parameterized by minimizing the error with respect to satellite estimates and surface energy balance (SEB) model outputs on each computing cell over the period 1979 to 2022. We evaluate the PDD model by performing a goodness-of-fit test and cross-validation. We assess the accuracy of our parameterization method, based on the performance of the PDD model when considering all computing cells as a whole, independently of the time window chosen for parameterization. We conduct a sensitivity experiment by adding ±10 % to the training data (satellite estimates and SEB model outputs) used for PDD parameterization and a sensitivity experiment by adding constant temperature perturbations (+1 , +2 , +3 , +4 and +5 ∘ C) to the 2 m air temperature field to force the PDD model. We find that the PDD melt extent and amounts change analogously to the variations in the training data with steady statistically significant correlations and that the PDD melt amounts increase nonlinearly with the temperature perturbations, demonstrating the consistency of our parameterization and the applicability of the PDD model to warmer climate scenarios. Within the limitations discussed, we suggest that an appropriately parameterized PDD model can be a valuable tool for exploring Antarctic surface melt beyond the satellite era. [ABSTRACT FROM AUTHOR]

We present a database of observational constraints on past Antarctic Ice Sheet changes during the last glacial cycle intended to consolidate the observations that represent our understanding of past Antarctic changes and for state-space estimation and paleo-model calibrations. The database is a major expansion of the initial work of Briggs and Tarasov (2013). It includes new data types and multi-tier data quality assessment. The updated constraint database, AntICE2 (https://theghub.org/resources/4884 , Lecavalier et al., 2022), consists of observations of past grounded- and floating-ice-sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. In addition to paleo-observations, the present-day ice sheet geometry and surface ice velocities are incorporated to constrain the present-day ice sheet configuration. The method by which the data are curated using explicitly defined criteria is detailed. Moreover, the observational uncertainties are specified. The methodology by which the constraint database can be applied to evaluate a given ice sheet reconstruction is discussed. The implementation of the AntICE2 database for Antarctic Ice Sheet model calibrations will improve Antarctic Ice Sheet predictions during past warm and cold periods and yield more robust paleo-model spin ups for forecasting future ice sheet changes. [ABSTRACT FROM AUTHOR]

The air-sea interaction in the Gulf of Guinea and its role in setting precipitation at the Guinean coast is investigated in the present paper. This study is based on satellite observations and WRF simulations forced by different sea surface temperature (SST) patterns. It shows that the seasonal cold tongue setup in the Gulf of Guinea, along with its very active northern front, tends to strongly constrain the low level atmospheric dynamics between the equator and the Guinean coast. Underlying mechanisms including local SST effect on the marine boundary layer stability and hydrostatically-changed meridional pressure gradient through changes in SST gradient are quantified in WRF regarding observations and CFSR reanalyses. Theses mechanisms strongly impact moisture flux convergence near the coast, leading to the installation of the first rainy season of the West African Monsoon (WAM) system. The current study details the mechanisms by which the Atlantic Equatorial cold tongue plays a major role in the pre-onset of the boreal WAM. [ABSTRACT FROM AUTHOR]

An airborne microwave wide-band radiometer (500–2000 MHz) was operated for the first time in Antarctica to better understand the emission properties of sea ice, outlet glaciers and the interior ice sheet from Terra Nova Bay to Dome C. The different glaciological regimes were revealed to exhibit unique spectral signatures in this portion of the microwave spectrum. Generally, the brightness temperatures over a vertically homogeneous ice sheet are warmest at the lowest frequencies, consistent with models that predict that those channels sensed the deeper, warmer parts of the ice sheet. Vertical heterogeneities in the ice property profiles can alter this basic interpretation of the signal. Spectra along the lengths of outlet glaciers were modulated by the deposition and erosion of snow, driven by strong katabatic winds. Similar to previous experiments in Greenland, the brightness temperatures across the frequency band were low in crevasse areas. Variations in brightness temperature were consistent with spatial changes in sea ice type identified in satellite imagery and in situ ground-penetrating radar data. The results contribute to a better understanding of the utility of microwave wide-band radiometry for cryospheric studies and also advance knowledge of the important physics underlying existing L-band radiometers operating in space. [ABSTRACT FROM AUTHOR]

We present a database of observational constraints on past Antarctic ice sheet changes during the last glacial cycle intended to consolidate the observations that represent our understanding of past Antarctic changes, for state-space estimation, and paleo-model calibrations. The database is a major expansion of the initial work of Briggs and Tarasov (2013). It includes new data types and multi-tier data quality assessment. The updated constraint database "AntICE2" consists of observations of past grounded and floating ice sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. In addition to paleo-observations, the present-day ice sheet geometry and surface ice velocities are incorporated to constrain the present-day ice sheet configuration. The method by which the data is curated using explicitly defined criteria is detailed. Moreover, the observational uncertainties are specified. The methodology by which the constraint database can be applied to evaluate a given ice sheet reconstruction is discussed. The implementation of the "AntICE2" database for Antarctic ice sheet model calibrations will improve Antarctic ice sheet predictions during past warm and cold periods and yield more robust paleo model spin ups for forecasting future ice sheet changes. [ABSTRACT FROM AUTHOR]

An ultrawideband radiometer was used to measure microwave brightness temperature spectra over Arctic sea ice in the Lincoln Sea near the north coast of Greenland. Spectra over the range of 0.5–2 GHz were compared to thermal infrared images collected during the airborne campaign and also compared to nearly concurrent Sentinel-1 C-band synthetic aperture radar (SAR) data. Based on those comparisons, spectral signatures were associated with thick multiyear ice and thin ice. A radiative transfer (RT) model consisting of a homogeneous slab of sea ice bounded by sea water and air was then used to invert the spectra for sea ice thickness and salinity. Inferred thicknesses were consistent with ice thickness climatology for ice floes in the Lincoln Sea. Salinities are higher than expected which may be a consequence of neglecting surface and volume scattering contributions in the models. [ABSTRACT FROM AUTHOR]

In this study, the relationship between trains of African easterly waves (AEWs) and downstream tropical cyclogenesis is studied. Based on 19 summer seasons (July-September from 1990 to 2008) of ERA-Interim reanalysis fields and brightness temperature from the Cloud User Archive, the signature ofAEWtroughs and embedded convection are tracked from the West African coast to the central Atlantic. The tracked systems are separated into four groups: (i) systems originating from the north zone of the midtropospheric African easterly jet (AEJ), (ii) those coming from the south part of AEJ, (iii) systems that are associated with a downstream trough located around 2000 km westward (termed DUO systems), and (iv) those that are not associated with such a close downstream trough (termed SOLO systems). By monitoring the embedded 700-hPa-filtered relative vorticity and 850-hPa wind convergence anomaly associated with these families along their trajectories, it is shown that the DUO generally have stronger dynamical structure and statistically have a longer lifetime than the SOLO ones. It is suggested that the differences between them may be due to the presence of the previous intense downstream trough in DUO cases, enhancing the low-level convergence behind them. Moreover, a study of the relationship between system trajectories and tropical depressions occurring between the West African coast and 40° Wshowed that 90% of tropical depressions are identifiable from the West African coast in tracked systems, mostly in the DUO cases originating from the south zone of the AEJ. [ABSTRACT FROM AUTHOR]

A large number of Atlantic tropical depressions are generated in the eastern basin in relation to the African easterly wave (AEW) and embedded mesoscale convective systems (MCSs) coming from the African continent. In this paper, the structures of strengthening and dissipating MCSs evolving near the West African coast are analyzed, including the role of the ocean surface conditions in their evolution. Satellite infrared brightness temperature and meteorological radar data over seven summer seasons between 1993 and 2006 are used to subjectively select 20 cases of strengthening and dissipating MCSs in the vicinity of the Senegal coast. With these observed MCSs, a lagged composite analysis is then performed using Interim ECMWF Re-Analysis (ERA-Interim) and Climate Forecast System Reanalysis (CFSR). It is shown that the strengthening MCS is generally preceded by prior passage of an AEW near the West African coast. This previous wave trough is associated with a convective cyclonic circulation in the low and middle troposphere, which enhances the southwesterly flow and then provides humidity to the strengthening MCS, located in the vicinity of the subsequent AEW trough. This is favored by the contraction of the wavelength associated with the two troughs. The sea surface contributes to the MCS enhancement through surface evaporation flux. But this contribution is found to be less important than advection of humidity from the previous wave trough. These conditions are almost not found in the dissipating MCS cases, which dissipate in a dry environment dominated by a subsident and anticyclonic circulation, with generally no interaction with a previous wave trough. [ABSTRACT FROM AUTHOR]

The "Cooperative Airborne Radiometer for Ocean and Land Studies" (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer-STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with in situ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity. [ABSTRACT FROM AUTHOR]

Microwave emissions at the L-band (1–2 GHz) in Antarctica are characterized by a significant contribution of ice layers at great depth, from hundreds to a thousand meters. Brightness temperatures, thus, could provide the internal temperature of the ice sheet. However, there are two difficulties to overcome in developing an accurate retrieval algorithm. First, it is difficult to know precisely from which depths waves are emanating because the ice-absorption coefficient is uncertain at the L-band, despite several formulations proposed in the literature over the past few decades. Second, emissivity potentially varies in Antarctica due to remnant scattering in firn (or ice), even at the Brewster angle, and despite the low frequency, limiting the accuracy of the estimate of the physical temperature. Here, we present a retrieval method able to disentangle the absorption and emissivity effects from brightness temperature over the whole continent. We exploit the fact that scattering and absorption are controlled by different physical parameters and phenomena that can be considered as statistically independent. This independence provides a constraint to the retrieval method, that is then well-conditioned and solvable. Our results show that (1) the retrieved absorption agrees with the permittivity model proposed by Mätzler et al. (2006), and (2) emissivity shows significant variations, up to 6% over the continent, which are correlated with wind speed and accumulation patterns. A possible cause of this latter point is density heterogeneity and sastrugi buried in the firn. These two results are an important step forward for the accurate retrieval of internal temperature using low-frequency microwave radiometers. [ABSTRACT FROM AUTHOR]