Earth-atmosphere System Research Articles

Observation and simulation study of atmospheric aerosol nonsphericity over the Loess Plateau in northwest China

Aerosol nonsphericity, which is not well depicted in model calculations, seriously affects aerosol optical properties and subsequently alters the radiative forcing of the earth–atmosphere system. Based on aerosol backscattering linear depolarization ratio data observed by a polarization lidar at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from September 2009 to August 2012 and numerical computations, the spatial and temporal distribution of the aerosol depolarization ratio, parameterization of the derived aspect ratio and influence of water vapor on aerosol nonsphericity were investigated. Aerosol nonsphericity varied considerably by season, with a pronounced maximum in the spring, when more nonspherical aerosols were transported upward to the free troposphere; moreover, the column-averaged lidar depolarization ratios were 0.13, 0.09, 0.08 and 0.10 for the spring, summer, autumn and winter, respectively. The derived aerosol aspect ratio, a simplified parameter that describes the particle nonsphericity, ranged from 1.00 to 1.30 and peaked at approximately 1.06. A modified log-normal function, which was fitted to the frequency distribution of the derived aspect ratios, yielded a log-normal distribution parameterization for this parameter and provided a better shape input for the aerosol optical modeling. The monthly averaged aspect ratios reached a maximum of 1.13 during the spring and a minimum of 1.04 in autumn. The depolarization ratios decreased significantly with column-integrated increasing precipitable water in summer when there was sufficient precipitable water.

Global distribution of mineral dust and its impact on radiative fluxes as simulated by WRF-Chem

Dust aerosols make a considerable contribution to the climate system and atmospheric hydrological cycle through their radiative and ice nuclei effects. This underlines the need for investigating the sources of dust aerosols, their transport pathways, and radiative forcing. Seasonal distribution of mineral dust around the globe and its impact on radiation fluxes is estimated using two simulations: a model setup that did not include dust aerosols; and an interactive experiment that included dust aerosols and their feedback to the atmosphere. Simulations were performed by the Weather Research and Forecasting with Chemistry (WRF-Chem) model for a 1-year period. The global annual mean dust optical depth (DOD) at 0.55 $$\upmu$$ m is estimated to be 0.057, with a spring peak value of 0.081 and an autumn minimum value of 0.039. Seasonal variation of atmospheric dust loading is shown to be associated with similar significant variation in shortwave and longwave direct radiation perturbation by dust, both at the surface and top of the atmosphere (TOA). The presence of mineral dust in the interactive simulation is estimated to exert a maximum net direct radiation perturbation in summer with values of $$-$$ 2.85 and $$-$$ 1.63 W m $$^{-2}$$ in clear-sky conditions at the surface and TOA, respectively. It also exerts a global annual net direct radiation perturbation of $$-$$ 1.86 and $$-$$ 1.09 W m $$^{-2}$$ at the surface and TOA, respectively. The surface cooling is attributed to the extinction of incoming solar radiation by dust aerosols, while negative perturbation at the TOA (which demonstrates cooling of the Earth-atmosphere system) is predominantly attributed to an increase in outgoing shortwave radiation.

The Characteristics of Ice Cloud Properties Derived from CloudSat and CALIPSO Measurements

Abstract The characteristics of ice clouds with a wide range of optical depths are studied based on satellite retrievals and radiative transfer modeling. Results show that the global-mean ice cloud optical depth, ice water path, and effective radius are approximately 2, 109 g m−2, and 48 , respectively. Ice cloud occurrence frequency varies depending not only on regions and seasons, but also on the types of ice clouds as defined by optical depth values. Ice clouds with different values show differently preferential locations on the planet; optically thinner ones ( < 3) are most frequently observed in the tropics around 15 km and in midlatitudes below 5 km, while thicker ones ( > 3) occur frequently in tropical convective areas and along midlatitude storm tracks. It is also found that ice water content and effective radius show different temperature dependence among the tropics, midlatitudes, and high latitudes. Based on analyzed ice cloud frequencies and microphysical properties, cloud radiative forcing is evaluated using a radiative transfer model. The results show that globally radiative forcing due to ice clouds introduces a net warming of the earth–atmosphere system. Those with < 4.0 all have a positive (warming) net forcing with the largest contribution by ice clouds with ~ 1.2. Regionally, ice clouds in high latitudes show a warming effect throughout the year, while they cause cooling during warm seasons but warming during cold seasons in midlatitudes. Ice cloud properties revealed in this study enhance the understanding of ice cloud climatology and can be used for validating climate models.

When smoke comes to town: The impact of biomass burning smoke on air quality

Biomass burning aerosols influence the radiative balance of the earth-atmosphere system. They also reduce visibility and impact human health. In addition, trace gases and aerosols emitted to the atmosphere during large biomass burning episodes may have a significant effect on atmospheric chemistry due to the presence of reactive species.Six hundred and ninety wildfires burned more than one million hectares in Victoria, Australia between December 2006 and February 2007. Thick smoke haze was transported to Melbourne (population 3.9 million) on several occasions, causing PM10 (particulate mass less than 10 μm in diameter) concentrations to exceed 200 μg m−3. The presence of elevated total secondary organic aerosol (SOA) and speciated SOA compounds (including pinene and cineole oxidation products), O3, and the larger aerosol mode diameter during smoke impacted periods indicated the presence of photochemical oxidation within the plume. The presence of organosulfate compounds and nitro-oxy organosulfate compounds indicated oxidation may have occurred in the presence of acidic seed aerosol and that oxidation may also have occurred at night.Older smoke plumes (aged 30 h) displayed higher concentrations of a number of gaseous and aerosol species relative to the younger smoke plumes (aged 3 h). SOA compounds made up a greater fraction of speciated organic mass in the old plume than in the young plume where speciated biomass burning compounds dominated. Cineole oxidation products made up a greater fraction of the speciated SOA compounds in the old plume while pinene oxidation products made up a greater fraction of the total SOA speciated mass in the samples from the young plume. This may be a result of the slower reaction rate of cineole with OH. Organosulfate compounds and nitro-oxy organosulfate compounds made up greater fractions of the speciated SOA mass in the old plume consistent with the production of nitro-oxy organosulfate compounds under night time conditions in the presence of acidic seed.These results suggest that enhanced photochemical activity occurs in smoke plumes and can significantly change the composition and microphysical properties of aerosol, potentially leading to changes in the optical and thus radiative properties of the aerosol.

Discrete Anisotropic Radiative Transfer (DART 5) for Modeling Airborne and Satellite Spectroradiometer and LIDAR Acquisitions of Natural and Urban Landscapes

Satellite and airborne optical sensors are increasingly used by scientists, and policy makers, and managers for studying and managing forests, agriculture crops, and urban areas. Their data acquired with given instrumental specifications (spectral resolution, viewing direction, sensor field-of-view, etc.) and for a specific experimental configuration (surface and atmosphere conditions, sun direction, etc.) are commonly translated into qualitative and quantitative Earth surface parameters. However, atmosphere properties and Earth surface 3D architecture often confound their interpretation. Radiative transfer models capable of simulating the Earth and atmosphere complexity are, therefore, ideal tools for linking remotely sensed data to the surface parameters. Still, many existing models are oversimplifying the Earth-atmosphere system interactions and their parameterization of sensor specifications is often neglected or poorly considered. The Discrete Anisotropic Radiative Transfer (DART) model is one of the most comprehensive physically based 3D models simulating the Earth-atmosphere radiation interaction from visible to thermal infrared wavelengths. It has been developed since 1992. It models optical signals at the entrance of imaging radiometers and laser scanners on board of satellites and airplanes, as well as the 3D radiative budget, of urban and natural landscapes for any experimental configuration and instrumental specification. It is freely distributed for research and teaching activities. This paper presents DART physical bases and its latest functionality for simulating imaging spectroscopy of natural and urban landscapes with atmosphere, including the perspective projection of airborne acquisitions and LIght Detection And Ranging (LIDAR) waveform and photon counting signals.

Geographically coherent patterns of albedo enhancement and suppression associated with aerosol sources and sinks

Earth's albedo is the primary determinant of the amount of energy absorbed by the Earth–atmosphere system. It is a function of the fractional cloud cover and the cloudy- and clear-sky albedos, and thereby of the aerosol loading of the atmosphere. Here, we introduce a method by which we can examine the spatial distribution of the albedo variability that is independent of variations in the two dominant factors of albedo: cloud fraction and liquid water path (LWP). The analysis is based on data simultaneously retrieved from the CERES and MODIS instruments carried on board the Aqua satellite. We analysed the daily overpass data between July 2002 and June 2014 and showed that perturbations in albedo, accounting for variations induced by cloud fraction and LWP, display a coherent geographical pattern. Positive deviations occur in proximity to known anthropogenic aerosol sources, and negative deviations coincide with areas of intense precipitation, acting as aerosol sinks. A simple multiplication of the observed positive perturbations in albedo with the solar flux of 340 W m−2 yields a magnitude of that effect of several watts per square meter locally. While the location and scale of the geographical pattern might suggest an anthropogenic contribution to the positive albedo perturbations, it is imperative to first carefully examine all other possible causal factors behind the perturbations. Finally, although we have not attempted a full calculation of detection limits, the analysis is capable of sensing very small changes in average albedo of the order of 0.003 out of a total albedo of the order of 0.3. Hence, the applied method might find utilisation in a variety of situations where there is a need to quantify small perturbations of a dependent variable in noisy global data sets.

Modelling the water budget of Ireland - evapotranspiration and soil moisture

The water budget is one of the most important exchange cycles within the earth-atmosphere system. When applied to a surface it accounts for the partition of precipitation into evapotranspiration. runoff and exchanges in soil-water storage. While there has been work published on some of these components, few have attempted to evaluate these within the context of the water budget. In this paper a simple model is applied to a 5x5km grid superimposed on the land area of Ireland. The model uses measured monthly values of meteorological variables (precipitation, temperature and sunshine hours) and databases of landuse and elevation to calculate each of the water budget terms. The results for the thirty year period 1961 -1 WO are presented and seem to conform to the known climate of the period.

The role of cloud height and warming in the decadal weakening of atmospheric heat source over the Tibetan Plateau

The warming over the Tibetan Plateau (TP) is very significant during last 30 years, but the thermal forcing has been weakened. The thermal weakening is attributed mainly to the enhancement of the TOA (top of atmosphere) outgoing radiation. This enhancement is opposite to the greenhouse-gas-induced weakening of the global mean TOA outgoing radiation and is also unable to be explained by the observed decrease of total cloud cover. This study presents the importance of cloud height change and the warming over the TP in modulating the TOA radiation budget and thus the thermal forcing during spring and summer. On the basis of surface observations and satellite radiation data, we found that both the TOA outgoing shortwave radiation and longwave radiation were enhanced during this period. The former enhancement is due mainly to the increase of low-level cloud cover, which has a strong reflection to shortwave radiation, especially in summer. The latter enhancement is caused mainly by the planetary warming, and it is further enhanced by the decrease of total cloud cover in spring, as clouds extinguish outgoing longwave radiation emitted from the land surface. Therefore, the radiative cooling enhancement and thus the thermal weakening over the TP is a response of the earth-atmosphere system to the unique change of cloud cover configuration and the rapid warming of the land surface. However, these trends in cloud cover and TOA outgoing radiation are not well represented in four reanalyses.

Diurnal Variations of Albedo Retrieved from Earth Radiation Budget Experiment Measurements

AbstractFive years of measurements from the Earth Radiation Budget Satellite (ERBS) have been analyzed to define the diurnal cycle of albedo from 55°N to 55°S. The ERBS precesses through all local times every 72 days so as to provide data regarding the diurnal cycles for Earth radiation. Albedo together with insolation at the top of the atmosphere is used to compute the heating of the Earth–atmosphere system; thus its diurnal cycle is important in the energetics of the climate system. A principal component (PC) analysis of the diurnal variation of top-of-atmosphere albedo using these data is presented. The analysis is done separately for ocean and land because of the marked differences of cloud behavior over ocean and over land. For ocean, 90%–92% of the variance in the diurnal cycle is described by a single component; for land, the first PC accounts for 83%–89% of the variance. Some of the variation is due to the increase of albedo with increasing solar zenith angle, which is taken into account in the ERBS data processing by a directional model, and some is due to the diurnal cycle of cloudiness. The second PC describes 2%–4% of the variance for ocean and 5% for land, and it is primarily due to variations of cloudiness throughout the day, which are asymmetric about noon. These terms show the response of the atmosphere to the cycle of solar heating. The third PC for ocean is a two-peaked curve, and the associated map shows high values in cloudy regions.

Climatology Of Thin Cirrus Clouds at Gadanki (13.5°N, 79.2°E) Using Ground Based Lidar And Satellite Based Measurements

Abstract. High altitude cirrus clouds play a significant role in the radiative balance of Earth atmosphere system. Information on cirrus occurrences and their optical properties is essential for climate modeling studies. The influence of high altitude thin cirrus clouds on the climate is important due to their optical and thermodynamic properties. In order to quantify their effect on atmosphere, the vertical structure and optical properties of these thin cirrus clouds are to be characterized. The Lidar technique has become a unique tool for detecting and characterizing cirrus clouds for their optical properties. Ground based LIDAR system offers an excellent way to obtain characteristic values on the cirrus formations, although the microphysical and optical properties of thin cirrus clouds can also obtained on global scale by the observations from Earth-orbiting Satellites .The ground-based lidar observations could provide more intensive measurements on continuous basis, compared to satellite observations. Utilising observations from both, the statistical characteristics, physical and optical properties of thin cirrus clouds can be retrieved more precisely. The present study is based on the ground based lidar measurements using the pulsed monostatic LIDAR system at the National Atmospheric Research Laboratory [NARL], Gadanki (13.5° N, 79.2° E), Andhra Pradesh, India. The data obtained in the altitude range of 8−20 km are used for this study. Cirrus observations made using CALIPSO and MODIS satellites are compared with the ground based lidar data for systematic statistical study of cirrus climatology. Optically thin cirrus clouds (τ < 0.3) observed during 2009 are selected and their microphysical and geometrical properties are studied. The microphysical properties such as optical depth, lidar ratio and depolarisation ratio for cirrus clouds were obtained. It is observed that the variability in optical depth depends on the composition and thickness of the clouds. The relationships between various quantities were also processed. The study shows that the thin cirrus generally was present in higher altitudes and the optical properties show correlation with the height and the temperature.

The influence of solar spectral variations on global radiative balance

The total solar irradiance (TSI) has been the sole solar input in many climate models for lack of long and reliable time series of solar spectral irradiance (SSI) measurements currently. However, based on the recent SSI measurements by the Solar Radiation and Climate Experiment, which is able to provide full and accurate SSI measurements, the influence of SSI variations on global radiative balance between the descending phase of previous solar cycle in December 2007 and the ascending phase of the current solar cycle in the first half 2010 has been studied in this paper. The results show that the relatively larger TSI in the first half 2010 was mainly due to the ultraviolet and near infrared radiation enhancements, with average increases of 0.11% in 200–400nm and 0.05% in 760–4000nm respectively, while the radiation in visible region of 400–760nm decreased by 0.05%. According to the measurements of ozone from the Aura-Microwave Limb Sounder satellite, the global average stratospheric ozone increased markedly in the layer of 25–40km at the same time. The visible radiation decrease and stratospheric ozone increase together contributed to the smaller solar radiation at the tropopause for each month of the first half 2010 as compared with that in December 2007, with the maximum decrease of 0.15Wm−2 in March 2010. The study reveals that SSI variations in the ascending solar phase may also cool the Earth-atmosphere system.

A method for sampling microbial aerosols using high altitude balloons

Owing to the challenges posed to microbial aerosol sampling at high altitudes, very little is known about the abundance, diversity, and extent of microbial taxa in the Earth-atmosphere system. To directly address this knowledge gap, we designed, constructed, and tested a system that passively samples aerosols during ascent through the atmosphere while tethered to a helium-filled latex sounding balloon. The sampling payload is ~2.7kg and comprised of an electronics box and three sampling chambers (one serving as a procedural control). Each chamber is sealed with retractable doors that can be commanded to open and close at designated altitudes. The payload is deployed together with radio beacons that transmit GPS coordinates (latitude, longitude and altitude) in real time for tracking and recovery. A cut mechanism separates the payload string from the balloon at any desired altitude, returning all equipment safely to the ground on a parachute. When the chambers are opened, aerosol sampling is performed using the Rotorod® collection method (40 rods per chamber), with each rod passing through 0.035m3 per km of altitude sampled. Based on quality control measurements, the collection of ~100cells rod−1 provided a 3-sigma confidence level of detection. The payload system described can be mated with any type of balloon platform and provides a tool for characterizing the vertical distribution of microorganisms in the troposphere and stratosphere.

The iodine-plutonium-xenon age of the Moon-Earth system revisited.

Iodine-plutonium-xenon isotope systematics have been used to re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radionuclides ((129)I, T1/2=15.6 Ma and (244)Pu, T1/2=80 Ma) have produced radiogenic (129)Xe and fissiogenic (131-136)Xe, respectively, within the Earth, the related isotope fingerprints of which are seen in the compositions of mantle and atmospheric Xe. Recent studies of Archaean rocks suggest that xenon atoms have been lost from the Earth's atmosphere and isotopically fractionated during long periods of geological time, until at least the end of the Archaean eon. Here, we build a model that takes into account these results. Correction for Xe loss permits the computation of new closure ages for the Earth's atmosphere that are in agreement with those computed for mantle Xe. The corrected Xe formation interval for the Earth-atmosphere system is [Formula: see text] Ma after the beginning of Solar System formation. This time interval may represent a lower limit for the age of the Moon-forming impact.

A thermodynamic hypothesis regarding optimality principles for flow processes in geosystems

This paper proposes a new thermodynamic hypothesis that states that a nonlinear natural system that is not isolated and involves positive feedbacks tends to minimize its resistance to the flow process through it that is imposed by its environment. We demonstrate that the hypothesis is consistent with flow behavior in saturated and unsaturated porous media, river basins, and the Earth-atmosphere system. While optimization for flow processes has been previously discussed by a number of researchers in the literature, the unique contribution of this work is to indicate that only the driving process is subject to optimality when multiple flow processes are simultaneously involved in a system.

Impact of Kalpana-1 derived land surface albedo on short-range weather forecasting over the Indian subcontinent

The skill of weather forecasts at high spatial resolution depends on accurate representation of land surface states at appropriate spatial and temporal scales that modulate flux partitioning in the numerical weather prediction models. In this study, the Weather Research and Forecasting (WRF) model is customized to assess the impact of land surface albedo (LSA) derived from Kalpana-1 Very High Resolution Radiometer (K1VHRR) in comparison to default monthly climatological albedo from the United States Geological Survey (USGS). A two-stage upscaling of ground-measured albedo from Agro-Met Stations is performed to derive K1VHRR LSA. This combines multispectral reflectance at intermediate scales from the Advanced Wide Field Sensor on board Resourcesat-2 at Low Earth Orbiting platform and the planetary (Earth-atmosphere system) albedo from Kalpana-1 visible band at Geostationary Earth Orbiting platform. Two separate experiments, with real-time K1VHRR LSA and USGS climatological LSA (CNT), are performed to evaluate the impact of real-time K1VHRR LSA on daily WRF model forecasts during July 2009. Additional experiments are performed to assess the impact of real-time and climatological K1VHRR albedo against USGS climatological albedo based experiment. Results show that real-time K1VHRR albedo improves the surface temperature, specific humidity, and wind speed forecasts as compared to CNT experiments. The impact of climatological and real-time K1VHRR LSA is small compared to the advantage of using K1VHRR over USGS. Moreover, real-time K1VHRR albedo has additional benefits to improve the representation of seasonal variability. Results show that the real-time K1VHRR LSA has slight positive impact on rainfall forecast.

Sensitivity analysis of single-angle polarization reflectance observed by satellite

Two channels of the Cloud Aerosol Polarimetric Imager, onboard the TanSat-Chinese carbon dioxide observation satellite, are designed to detect the polarization state of radiation reflected by the earth-atmosphere system in a single-viewing angle. Aiming to understand how the earth and atmospheric parameters affect the polarization state of radiation, we conduct a sensitivity analysis of the polarized reflectance at the top of atmosphere (TOA) with respect to the aerosol microphysical parameters, atmospheric profiles, and surface polarization properties. It is found that (1) the TOA polarization reflectance at 0.66 μm is most sensitive to the real part of the aerosol complex refractive index, the mean radius of the fine mode aerosol particles, as well as atmospheric pressure and temperature profiles; (2) the TOA polarization reflectance at 1.64 μm is sensitive to the volume ratio between the coarse mode and fine mode particles as well, but it is not sensitive to atmospheric profiles; and (3) surface polarization properties have a relatively weak influence on the TOA polarization reflectance at both 0.66 and 1.64 μm.

Modeling polarized solar radiation from the ocean–atmosphere system for CLARREO inter-calibration applications

Abstract. Reflected solar radiance from the Earth–atmosphere system is polarized. Radiance measurements can be affected by light's state of polarization if the radiometric sensor has polarization dependence. To enable the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission for inter-calibration of the imagers with polarization dependence, such as the MODIS, the polarization state of the light must be known with sufficient accuracy. For this purpose, the polarized solar radiation from the ocean–atmosphere system is studied with an adding-doubling radiative transfer model (ADRTM). The Cox–Munk ocean wave slope distribution model is used in calculation of the reflection matrix of a wind-ruffled ocean surface. An empirical foam spectral reflectance model and an empirical spectral reflectance model for water volume below the surface are integrated in the ocean-surface model. Solar reflectance from the ADRTM is compared with that from the discrete-ordinate radiative transfer (DISORT) model. Sensitivity studies are conducted for various ocean-surface and atmospheric conditions for the stratification of polarization distribution models (PDMs), which are to be used in the inter-calibration of the polarization-sensitive imager measurements with the CLARREO data. This report presents the first accurate approach for making the spectral PDMs over broad solar spectra, which cannot be achieved by empirical PDMs based on the data from polarimetric sensors.

Evolution of volatile species in the earth’s mantle: A view from xenology

To understand the scales and chronology of processes governing the evolution of terrestrial gas species, the constraints from 244Pu–238U–129I–Xe systematics are crucial and should be included in any model related to gas loss/gain by the Earth and to gas redistribution among terrestrial reservoirs.Reliable constraints can be derived from meteoritic and terrestrial abundances of the highly refractory lithophile incompatible parent isotopes 244Pu (half life τ244=80.0Myr) and 238U (τ238=4468Myr). Both isotopes produce heavy Xe isotopes by fission; different relative yields for the Xe isotopes allow contributions of Xe(Pu) and Xe(U) to be distinguished. It is also useful to consider the 129I–129Xe(I) systematics (τ129=15.6Myr) even though iodine is a highly volatile element and its terrestrial abundance is less well known. The parent isotopes, for which the initial (at the time of formation of the solar system, 4.567Gyr ago) abundances are known from investigations of meteorites and ancient terrestrial zircons, yield the closed-system (subscript CLOS) present-day ratios of [136Xe(Pu)/136Xe(U)]CLOS=28 and [129Xe(I)/136Xe(Pu)]CLOS=110, much exceeding values observed in the depleted heterogeneous mantle reservoir (DMR): [136Xe(Pu)/136Xe(U)]DMR⩽3 and [129Xe (I)/136Xe(Pu)]DMR⩽60 (Pepin and Porcelli, 2006). Also, the present-day amounts of 129Xe(I) in the mantle (∼0.01Tmol) and in the atmosphere (0.278Tmol) are well below the total value produced by decay of 129I (129Xe (I)=35Tmol). These relationships between the closed system and the observed values show loss of early-produced Xe isotopes occurred not only from the DMR, but also from the Earth–atmosphere system as a whole.Using abundances of the parent and daughter isotopes within the framework of a simple one-mantle-reservoir degassing model we conclude: (1) the present day mantle is a severely degassed reservoir, so that only<10−3 of the initially available amount of stable Xe atoms (e.g., 130Xe) has survived 4.567Gyr of degassing. This low retention parameter is practically model-independent, as any solution is governed by the requirement of almost total 136Xe(Pu) loss from the mantle. (2) The degassing rate as a function of time appears to be the most reliable constraint on mantle convection in the past. To ensure intense early degassing, the rate of mantle convection during the Hadean era must exceed the present day value by up to a factor of ∼100. These two issues also follow from the study of two mantle reservoir models: if primordial and early-produced species were added into the convecting mantle from a hypothetical early-formed reservoir, the mantle itself must be degassed to a higher rate than that predicted by the one-mantle-reservoir model. This is in contrast to the very model dependent issue (3): the one-mantle-reservoir degassing model predicts a rather late time for atmosphere closure to Xe loss, between 3.5 and 4Gyr ago (possibly even extending to the Archean).Several recent mantle evolution models (based on U–Th–He and K–Ar isotope systematics) postulate a low overall degassing of the Earth and are inconsistent with these results from mantle xenology.

Radiative transfer modeling in the Earth–Atmosphere system with DART model

The atmosphere strongly affects satellite measurements of Earth surfaces in the optical domain. Modeling this influence is complex. This is typically the case of the “Earth–Atmosphere” radiative coupling in the presence of Earth surfaces with spatially variable optical properties. In that case, it may be very difficult to couple Earth and cloud-free atmosphere radiative transfer models. This explains why an atmosphere module was input into the Earth radiative transfer (R.T.) model DART (Discrete Anisotropic Radiative Transfer) in order to simulate accurately satellite images of natural and urban Earth surfaces. This paper presents how DART simulates the atmosphere R.T. in the short wave and thermal infrared domains. The atmosphere is divided into 3 zones: bottom atmosphere (BA), mid atmosphere (MA) and high atmosphere (HA). The 3D distribution is arbitrary in BA and horizontally constant with any vertical distribution in MA and HA. The “Earth–Atmosphere” R.T. is modeled in 5 stages. 1) Atmosphere R.T. (i.e., atmosphere thermal emission and/or sun radiation scattering). 2) Earth surface R.T. (i.e., Earth thermal emission and/or atmosphere and direct sun radiation scattering). 3) Atmosphere R.T. (i.e., Earth radiation scattering). 4) Earth surface R.T. (i.e., scattering of downward atmosphere radiation). 5) Simulation of satellite reflectance and/or brightness temperature images. The approach takes into account the earth curvature and the atmosphere non-Beer law behavior in the presence of strongly varying spectral properties. It uses optimally located scattering points for improving atmosphere R.T. accuracy, and it reduces computer time through the use of pre-computed transfer functions that transfer radiation between the different atmosphere levels (BA, MA, HA). Moreover, it can simulate automatically an atmosphere geometry that optimizes the trade-off “Computer time–Accuracy” of simulations. The robustness and accuracy of the DART atmosphere modeling were successfully validated with theoretical cases and with the MODTRAN atmosphere R.T. model.

Discriminating sea ice from low-level water clouds in split-window, mid-wavelength IR imagery

A technique is demonstrated to enhance the contrast between sea ice and low-level water clouds. The approach uses the brightness temperature difference (BTD) feature from data collected in the split-window, mid-wavelength infrared (IR) region (i.e. two bands at 3.7 μm and 4.0 μm). These spectral data are available with Visible Infrared Imager Radiometer Suite (VIIRS) moderate-resolution bands M12 and M13, respectively. Under daytime conditions, the data collected in these bands contain energy that originates from both the sun and the Earth–atmosphere system. Due to the small wavelength difference between these, the terrestrial energy component in the bands is typically quite similar as are the surface reflectances for sea ice and ocean surfaces. Thus, the enhanced contrast between sea ice and water clouds, evident in a M12–M13 BTD image, results from differences in the solar energy, which decreases rapidly across this atmospheric window. Observed BTD values for water clouds can exceed 30K, while those for snow-ice fields are typically much smaller (e.g. 0–5K). Thus, water clouds appear bright in the image while sea ice, oceans, and most land surfaces are very dark. The enhanced contrast in the split-window, mid-wave IR BTD image makes it valuable for both image analysis and use in cloud algorithms. In addition, these images support the creation of manually generated cloud masks that have been shown useful for quantitatively evaluating the performance of automated cloud analysis algorithms and cloud forecast models. In this article, the value of 3.7 μm minus 4.0 μm BTD imagery for distinguishing between sea ice and low-level water clouds is shown using VIIRS data collected over the Beaufort Sea on 31 May 2012. Manually generated cloud masks, derived in part from these data, are then used to quantitatively evaluate the effectiveness of various cloud tests, including those used in the VIIRS cloud mask algorithm and the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask algorithm. The results strongly suggest that split-window, mid-wavelength IR imagery provides valuable information to help differentiate between clouds and sea ice. It is concluded that collecting data in these mid-wavelength IR bands should be considered part of any future satellite sensor designed for environmental monitoring, especially over the polar regions.