Surface-atmosphere Interactions Research Articles

A downscaling method for distributing surface soil moisture within a microwave pixel: Application to the Monsoon '90 data

A downscaling method for the near-surface soil moisture retrieved from passive microwave sensors is applied to the PBMR data collected during the Monsoon '90 experiment. The downscaling method requires (1) the coarse resolution microwave observations, (2) the fine-scale distribution of soil temperature and (3) the fine-scale distribution of surface conditions composed of atmospheric forcing and the parameters involved in the modeling of land surface–atmosphere interactions. During the Monsoon '90 experiment, eight ground-based meteorological and flux stations were operating over the 150 km 2 study area simultaneously with the acquisition of the aircraft-based L-band PBMR data. The heterogeneous scene is hence composed of eight subpixels and the microwave pixel is generated by aggregating the microwave emission of all sites. The results indicate a good agreement between the downscaled and ground-based soil moisture as long as the intensity of solar radiation is sufficiently high to use the soil temperature as a tracer of the spatial variability of near-surface soil moisture.

Mars atmospheric surface interactions and the CO2 cycle

Mars' northern and southern seasonal polar caps are formed during their respective autumn and winter seasons both by condensation of atmospheric carbon dioxide (CO2) directly onto the surface, and through atmospheric precipitation in the form of CO2 snow. During the polar spring and summer, the seasonal ice sublimes, returning CO2 to the atmosphere.Roughly 25% of the atmosphere, which is 95% CO2 by volume, is cycled through the seasonal caps annually. This CO2 cycle dominates atmospheric circulation on Mars and must be thoroughly understood before the fundamental questions about Mars' climate history and the global distribution of near‐surface water can be addressed.

A combined modeling and multispectral/multiresolution remote sensing approach for disaggregation of surface soil moisture: application to SMOS configuration

A new physically based disaggregation method is developed to improve the spatial resolution of the surface soil moisture extracted from the Soil Moisture and Ocean Salinity (SMOS) data. The approach combines the 40-km resolution SMOS multiangular brightness temperatures and 1-km resolution auxiliary data composed of visible, near-infrared, and thermal infrared remote sensing data and all the surface variables involved in the modeling of land surface-atmosphere interaction available at this scale (soil texture, atmospheric forcing, etc.). The method successively estimates a relative spatial distribution of soil moisture with fine-scale auxiliary data, and normalizes this distribution at SMOS resolution with SMOS data. The main assumption relies on the relationship between the radiometric soil temperature inverted from the thermal infrared and the microwave soil moisture. Based on synthetic data generated with a land surface model, it is shown that the radiometric soil temperature can be used as a tracer of the spatial variability of the 0-5 cm soil moisture. A sensitivity analysis shows that the algorithm remains stable for big uncertainties in auxiliary data and that the uncertainty in SMOS observation seems to be the limiting factor. Finally, a simple application to the SGP97/AVHRR data illustrates the usefulness of the approach.

The Planetary Fourier Spectrometer (PFS) onboard the European Mars Express mission

The Planetary Fourier Spectrometer (PFS) for the Mars Express mission is an infrared spectrometer optimised for atmospheric studies. This instrument has a short wave (SW) channel that covers the spectral range from 1700 to 8200.0 cm - 1 (1.2– 5.5 μ m ) and a long-wave (LW) channel that covers 250– 1700 cm - 1 (5.5– 45 μ m ). Both channels have a uniform spectral resolution of 1.3 cm - 1 . The instrument field of view FOV is about 1 . 6 ∘ (FWHM) for the Short Wavelength channel (SW) and 2 . 8 ∘ (FWHM) for the Long Wavelength channel (LW) which corresponds to a spatial resolution of 7 and 12 km when Mars is observed from an height of 250 km. PFS can provide unique data necessary to improve our knowledge not only of the atmosphere properties but also about mineralogical composition of the surface and the surface-atmosphere interaction. The SW channel uses a PbSe detector cooled to 200–220 K while the LW channel is based on a pyroelectric ( L i T a O 3 ) detector working at room temperature. The intensity of the interferogram is measured every 150 nm of physical mirrors displacement, corresponding to 600 nm optical path difference, by using a laser diode monochromatic light interferogram (a sine wave), whose zero crossings control the double pendulum motion. PFS works primarily around the pericentre of the orbit, only occasionally observing Mars from large distances. Each measurements take 4 s, with a repetition time of 8.5 s. By working roughly 0.6 h around pericentre, a total of 330 measurements per orbit will be acquired 270 looking at Mars and 60 for calibrations. PFS is able to take measurements at all local times, facilitating the retrieval of surface temperatures and atmospheric vertical temperature profiles on both the day and the night side.

Modelling and measuring the spectral bidirectional reflectance factor of snow‐covered sea ice: an intercomparison study

AbstractBroadband albedo is a very important geophysical parameter in the Earth surface–atmosphere interaction in either global climate change or hydrological cycle and snowmelt runoff studies. To derive the broadband albedo accurately from satellite optical sensor observation at limited bands and at a single observation angle, the bidirectional reflectance factor (BRF) has to be specified quantitatively. In the present albedo derivation algorithms from the satellite radiance data, the BRF is either modelled or observed. Questions may arise as to how well a BRF model can be in the broadband albedo derivation. To help answer such questions, we studied the performance of a snow‐surface BRF model for two specific cases under large solar zenith angles (65° and 85°). We measured snow‐surface spectral directional reflectance under clear skies. The snow physical properties, such as snow grain size and snow density, at the same sites were also measured. In situ snow physical data are used to simulate the snow‐surface BRF and hemispherical directional reflectance factor (HDRF) through a multilayered azimuth‐ and zenith‐dependent plane‐parallel radiative transfer model. The field measurements and BRF and HDRF simulations all reveal the forward‐scattering nature of snow surface under large solar incidence angles, but the BRF model results depict the strongest forward‐scattering patterns under such solar zenith angles. Because the HDRF is simulated through coupling of the surface BRF with radiative transfer in the atmosphere, the resulting HDRF patterns agree with the field measurements better than the simulated BRF does. The deviation of the simulated HDRF from field‐based clear‐sky directional reflectance (FCDR) is within ±10% for the central (viewing zenith angle <45° ) and lateral sides of the viewing hemisphere. This level of agreement between the simulated HDRF and FCDR also implies that the simulated BRF model can provide remote‐sensing estimates of spectral albedo with an uncertainty of ±10% for the same part of the viewing hemisphere. Further improvement in BRF model performance requires better handling of single scattering properties of snow grains, surface roughness, and atmospheric correction. Also, better procedures and techniques in field measurement are necessary for more accurate assessment of the performance of BRF models. Copyright © 2004 John Wiley & Sons, Ltd.

Hydrologic processes in China and their association with summer precipitation anomalies

A climate version of MM5 is applied to study hydrologic processes in China and their association with precipitation anomalies in 1980 and 1985, which are two anomalous years with opposite signs of summer precipitation anomalies. The study reveals that anomalous atmospheric moisture transport due to synoptic scale circulation was primarily responsible for initiating the anomalous wet (dry) summer in south-central China and dry (wet) summer in northeastern China in 1980 (1985). The recycling ratio (defined as contribution of local evaporation to total precipitation) ranges from less than 4% in northwestern China to more than 30% in south-central China at 1000 km space scale. Higher (lower) values of recycling ratio correspond to drier (wetter) summers in south-central China and northeastern China. However, the opposite is true in northwestern China. The recycling ratio reflects feedback among hydrologic components over both land and atmosphere. In northwestern China, these feedbacks will further sustain drought events that are triggered by anomalous synoptic scale disturbances, and turn them into prolonged and possibly perpetual phenomenon. However, in south-central China and northeastern China, these feedbacks help reducing severity of drought. The large differences in recycling ratio between the dry and wet years of 1980 and 1985 are indicative of powerful feedback between hydrologic and climatic processes, and imply that surface-atmosphere interaction in China is highly sensitive to climatic perturbation.

Investigation of the application of aerobot technology at Venus

Robotic aerovehicles, or aerobots, can perform long duration detailed studies of planetary surfaces and atmospheres in three dimensions. Here we explore specific abilities of an aerobot mission to Venus using two concept missions: the Balloon Experiment at Venus (BEV) and the Venus Flyer Robot (VFR). Oscillating between 40 and 60 km altitude, the BEV is designed to collect atmospheric data over a nominal lifetime of weeks as well as image the surface. The VFR, with its ability to descend to the surface, can collect cm–m scale visible and near-infrared images of the surface, collect compositional and dynamical data of the lower atmosphere, and measure the composition of the Venus surface with a snake-mounted detector. These concept missions are used to calculate sample aerobot trajectories and descent scenarios which utilize variations in wind speed, altitude and surface slopes to maximize data collection. The trajectories are applied to two example geotraverses across Atla Regio and Ovda Regio. Data collected at these or similar targets by an aerobot can address several unresolved questions about Venus such as the nature of the lower atmosphere and atmosphere-surface interactions and the presence or absence of continental crust.

A simple model for minimum crop temperature forecasting during nocturnal cooling

A simple mechanistic model is developed to forecast the minimum temperature reached by the aerial elements of a crop during nocturnal cooling. The model, whose inputs are meteorological data registered at sunset, has two main characteristics: (1) it uses as a framework a two-layer scheme of the surface–atmosphere interaction which allows one to make a clear difference between the temperature of the crop and the temperature of the soil surface; (2) it does not deal with the rather complex resolution of the non-steady-state regime that most of the physical models intend to solve numerically or analytically; it is based upon a static representation of the soil–plant–atmosphere system assumed to be representative of the conditions reached at the end of the night, when minimum temperatures usually occur. The outputs of the model, i.e. minimum crop and soil surface temperatures, are compared to a set of experimental data collected on a pea crop grown near Paris in winter. It appears that the accuracy of the prediction depends mainly on the correct estimation of the nocturnal atmospheric radiation from the weather data observed at sunset. The model performs relatively well under clear sky conditions, but it is less accurate under cloudy conditions. Two simple procedures of estimating long-wave radiation are tested: their accuracy, however, turns out to be relatively poor. When used predictively, the model shows that all other conditions being kept equal, taller crops experience less severe frosts, while crops with greater leaf area index (LAI) experience more severe frosts. The role of soil characteristics (composition, moisture) is also assessed.

Comparison of energy fluxes at the land surface-atmosphere interface in an Alpine valley as simulated with different models

Abstract. Within the framework of a research project coupling meteorological and hydrological models in mountainous areas a distributed Snow-Soil-Vegetation-Atmosphere Transfer model was developed and applied to simulate the energy fluxes at the land surface – atmosphere interface in an Alpine valley (Toce Valley - North Italy) during selected flood events in the last decade. Energy fluxes simulated by the distributed energy transfer model were compared with those simulated by a limited area meteorological model for the event of June 1997 and the differences in the spatial and temporal distribution. The Snow/Soil-Vegetation-Atmosphere Transfer model was also applied to simulate the energy fluxes at the land surface-atmosphere interface for a single cell, assumed to be representative of the Siberia site (Toce Valley), where a micro-meteorological station was installed and operated for 2.5 months in autumn 1999. The Siberia site is very close to the Nosere site, where a standard meteorological station was measuring precipitation, air temperature and humidity, global and net radiation and wind speed during the same special observing period. Data recorded by the standard meteorological station were used to force the energy transfer model and simulate the point energy fluxes at the Siberia site, while turbulent fluxes observed at the Siberia site were used to derive the latent heat flux from the energy balance equation. Finally, the hourly evapotranspiration flux computed by this procedure was compared to the evapotranspiration flux simulated by the energy transfer model. Keywords: energy exchange processes, land surface-atmosphere interactions, turbulent fluxes

Remote sensing parameterization of the processes of energy and water cycle over desertification areas

In order to understand the processes of land surface-atmosphere interaction over desertification area, it is indispensable to utilize of satellite remote sensing. Two scenes of Landsat TM were used to produce a set of maps of surface reflectance, MSAVI, vegetation coverage, surface temperature, net radiation, soil heat flux, sensible heat flux and latent heat flux. Statistical analysis based on these maps revealed some quantitative significant land surface characteristics. Future developments of the method are also discussed.

Assimilating remote sensing data in a surface flux–soil moisture model

AbstractA key state variable in land surface–atmosphere interactions is soil moisture, which affects surface energy fluxes, runoff and the radiation balance. Soil moisture modelling relies on parameter estimates that are inadequately measured at the necessarily fine model scales. Hence, model soil moisture estimates are imperfect and often drift away from reality through simulation time. Because of its spatial and temporal nature, remote sensing holds great promise for soil moisture estimation. Much success has been attained in recent years in soil moisture estimation using passive and active microwave sensors, but progress has been slow. One reason for this is the scale disparity between remote sensing data resolution and the hydrologic process scale. Other impediments include vegetation cover and microwave penetration depth. As a result, currently there is no comprehensive method for assimilating remote soil moisture observations within a surface hydrology model at watershed or larger scales.This paper describes a measurement–modelling system for estimating the three‐dimensional soil moisture distribution, incorporating remote microwave observations, a surface flux–soil moisture model, a radiative transfer model and Kalman filtering. The surface model, driven by meteorological observations, estimates the vertical and lateral distribution of water. Based on the model soil moisture profiles, microwave brightness temperatures are estimated using the radiative transfer model. A Kalman filter is then applied using modelled and observed brightness temperatures to update the model soil moisture profile.The modelling system has been applied using data from the Southern Great Plains 1997 field experiment. In the presence of highly inaccurate rainfall input, assimilation of remote microwave data results in better agreement with observed soil moisture. Without assimilation, it was seen that the model near‐surface soil moisture reached a minimum that was higher than observed, resulting in substantial errors during very dry conditions. Updating moisture profiles daily with remotely sensed brightness temperatures reduced but did not eliminate this bias. Copyright © 2002 John Wiley & Sons, Ltd.

Editorial: Special issue on atmosphere-surface interactions

Editorial: Special issue on atmosphere-surface interactions

Radiocarbon on Titan

Abstract— We explore the likely production and fate of 14C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of 14C might place on Titan's photochemical, atmospheric transport and surface‐atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic‐ray flux limits the production of 14C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ˜9 atom/cm2/s, ˜4x higher than Earth. The fate and detectability of 14C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the 14C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identify locations where surface deposits of such material are “freshest”.

Experimental studies of atmosphere-surface interactions on Venus

We review the sulfur cycle, oxidation state of the surface and near-surface atmosphere, and the decomposition rate of fossil hydrous minerals on the surface of Venus. For each of these chemical weathering processes we discuss what has been learned and what key questions remain unanswered. We focus on these three types of atmosphere-surface interactions because they appear to play major roles in determining the composition of the atmosphere, clouds, and the surface, e.g. by serving as a sink for SO 2, by controlling the extent and rate of basalt oxidation, or by acting as a sink/source for atmospheric water. Unfortunately, no direct mineralogical data exist for the Venusian surface. Currently, the only way to study atmospheric-surface chemistry on Venus is through laboratory experiments. The results from these experiments will help guide the design of future spacecraft experiments that could make direct mineralogical observations by using techniques such as XRB and/or imaging infrared reflectance spectroscopy. These experimental results along with direct mineralogical data could prove or invalidate models proposed over the years.

Aircraft observations of surface–atmosphere exchange during and after snow melt for different arctic environments: MAGS 1999

AbstractThe arctic environment, and in particular the Mackenzie Basin, displays a very dynamic interrelationship between the atmosphere and the surface for the different ecosystems represented. The Canadian Twin Otter research aircraft flew a total of 24 grid and long regional transects, over tundra, forest and delta ecosystems, during the period of snow melt (late May–early June) and early summer (early July) as part of the 1999 Mackenzie Area GEWEX (Global Energy and Water Cycle Experiment) Study (MAGS) field campaign. Observations over tundra showed a sharp rise in the sensible heat flux at the onset of melt, reaching a maximum at the end of the melting period similar to those observed in early summer. The latent heat flux showed a more gradual rise from snowmelt to early summer with a Bowen ratio (sensible heat/latent heat) of two during melt. The forested system demonstrated a similar gradual rise in the latent heat flux, whereas the sensible heat flux was already high with Bowen ratios reaching three at the start of the observation period in late May. The gradual rise in latent heat flux can be tied to gradual thawing of the root zone and the onset of photosynthesis activity. The relatively low solar elevation angle and earlier start of snow melt along the regional transect may account for the much larger sensible heat flux. An analysis of the turbulent coherent structures indicates that the spatial density of structures for both latent heat and sensible heat increases strongly with season, from snow melt into the early summer conditions. This has implications for sampling criteria and optimum flux averaging period.There are distinct differences in energy partitioning between the various arctic ecosystems. At the beginning of the observation period, almost all the net radiation over the delta and tundra regions is utilized in non‐turbulent form, whereas the forested areas use less than 50%. Model simulations of the ground heat flux showed observed diurnal imbalances and suggest that the magnitudes depend on the position of the permafrost table and may partially account for the large non‐turbulent energy. Preliminary results from the Canadian MC2 model using the MAGS aircraft data for diagnosis and validation have identified sensitive model components that may merit further investigation. The findings from this study will help to fill gaps in our knowledge about surface–atmosphere interactions in arctic environments, particularly during snow melt, and broadens our contemporary view of evapotranspiration dynamics of wet surfaces. Copyright © 2001 John Wiley & Sons, Ltd.

Comparison of surface meteorological variables from TOVS and AVHRR

This paper examines, on global and continental spatial scales, the relationship between surface meteorological observations retrieved from the Advanced Very High Resolution Radiometer (AVHRR) and the TIROS Operational Vertical Sounder (TOVS). Comparisons of spatial and temporal patterns of surface temperature, air temperature, and vapor pressure deficit were carried out using data acquired between January 1989 and December 1990 on a monthly time step. These variables play an important role in hydrological, ecological, and land surface–atmosphere interactions. Additional comparisons were done for seven large regions (ca. 10 6 km 2) centered on the continental land surface areas in order to test for regional differences and to reduce the effect of coastal transition zones on spatial resampling. The mean statistical differences between the TOVS and AVHRR estimates were 5 °C for surface temperature, 4 °C for air temperature, and 1.5 kPa for vapor pressure deficit. In addition to long-term and spatially extensive ground data sets, these comparisons provide independent validation of different estimation methods using various satellite sensor measurements resampled to comparable spatial scales. Favorable comparison of the two sensors considered here provide greater confidence in the use of these data sets for global monitoring and modeling applications.

Wind-Related Modification of Some Small Impact Craters on Mars

Inferred wind-related modifications of impact craters are observed in the vicinity of the Mars Pathfinder (MPF) site and in other regions of Mars. Mars Obiter Camera (MOC) images show three types of inferred wind-modified morphologies for craters 0.3–1 km in diameter. Such modifications could be related to seasonal variations of the strongest winds and a possible paleowind regime. Geomorphic mapping of Big Crater at the MPF shows evidence of former aeolian modification of the crater rim and interiors similar to smaller craters in the area. The morphologic patterns are in good agreement with the results from the Mars Regional Atmospheric Modeling Simulation (MRAMS) of topographically forced wind circulation and atmosphere-surface interactions generated by flow over small craters. Simulations show that the maximum surface stress is on the downwind crater rim, consistent with inferred wind modification of the crater rim seen in MOC images. The trend of the inferred paleowind regime at the MPF site cannot be explained by a change in the global atmospheric circulation resulting from changes in Mars' obliquity. We suggest that this wind regime could be associated with a regional meteorological pattern that is not modeled by global scale circulation. An alternative explanation is that Mars' spin axis was in a different geographic position than it is at present.

The Mars Regional Atmospheric Modeling System: Model Description and Selected Simulations

The Mars regional atmospheric modeling system (MRAMS) is introduced, and selected model results are presented and compared with landed meteorological data when possible. MRAMS is descended from a nonhydrostatic Earth mesoscale and cloud-scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain. Mesoscale models such as MRAMS are ideal tools for making use of the high-resolution data sets arriving from Mars Global Surveyor experiments. Simulation of the Mars Pathfinder (MPF) landing site at L s=142 using 1/2 degree Mars orbiter laser altimeter (MOLA)-derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near-surface temperature, pressure, and wind direction. Simulations of topographically induced thermal circulations and mountain-induced gravity waves are shown to be consistent with theory and earlier studies that tie large-amplitude mountain waves to strong winds capable of producing dust streaks and local dust-lifting events. A large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux, momentum flux, turbulent kinetic energy, and vertical velocity variance. The model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon, but fluxes are roughly an order of magnitude smaller due to the lower density. Dust-devil-like circulations are also predicted in the large eddy simulation. Finally, a simulation that examines atmosphere–surface interactions near Big Crater is discussed. Predicted surface wind stress patterns are consistent with aeolian processes inferred through Mars Orbiter Camera imagery of Big Crater, located near the MPF landing site.

Mass independent oxygen isotopic composition of atmospheric sulfate: Origin and implications for the present and past atmosphere of Earth and Mars

It is reported that atmospheric (aerosol and rainwater) sulfate possesses a mass independent isotopic composition, with excess 17O. Laboratory experiments indicate that the oxidants, H2O2 and O3, are the source of anomalous 17O enrichments in atmospheric sulfate via aqueous phase S(IV) oxidation. The discovery of the oxygen anomaly in atmospheric sulfate, with definition of its origin, provides a new way to investigate atmospheric and general planetary processes. The observations provide new insight into atmospheric chemistry with application in studies of the evolution of the atmosphere, and surface‐atmosphere interactions, both on Earth and Mars.

A Statistical–Dynamical Parameterization of Interception and Land Surface–Atmosphere Interactions

At a local scale, the interception capacity of the canopy depends on a variety of climatic and canopy factors. Of particular importance is the intensity of rainfall—interception capacity varies inversely with rainfall intensity. At a field or regional scale, like the scale of global climate models, the spatially averaged interception also depends significantly on the spatial variability of rainfall intensity and total precipitation depth. A new parameterization of canopy interception is developed. In the new parameterization, the spatial average of actual interception is obtained as a function of rainfall intensity and total precipitation depth, and of an interception capacity, which depends on the characteristics of the leaf surface and of the vegetation cover. In a statistical‐dynamical framework, the new parameterization also accounts for the subgrid-scale spatial variability of rainfall intensity and total precipitation depth. The implications of accounting for the dependence of interception capacity on rainfall characteristics are examined by assessing the consequent responses of the energy and the water fluxes at the land surface. This is accomplished by incorporating the new parameterization into a soil‐plant‐atmosphere column model that is fundamentally based on the physical parameterizations of NCAR’s Community Climate Model.