Earth and Space Science

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Wiley Online Library : Earth and Space Science
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Issue Information

Fri, 03/09/2018 - 15:40

No abstract is available for this article.

Introducing a new inventory of large Martian landslides

Thu, 03/01/2018 - 20:27
Abstract

Landslides have been observed in different terrestrial environments and also on planets, satellites, and asteroids. Long runout landslides are strongly dependent on the initial mass position, material and slope path properties, topographic relief, and presence of volatiles. Therefore, landslides represent a means for the description of rock properties and environment of deposition prevailing at the time of occurrence, and may assist understanding the geological and climatological history of the planetary surfaces. Concerning Mars, previous studies have concentrated on Valles Marineris, where among the largest and longest landslides have been observed. Using different imagery, we present and analyse an original database of 3,118 Martian landslides of deposit area greater than 0.1 km2 throughout the planet between 60°n and 60°S, resulting in a dataset far richer than previously done. After a distinction is made between different typologies of landslides, their position and the statistical distribution of their geometrical properties are examined. Large landslides cluster along the Noctis Labyrinthus – Valles Marineris – Margaritifer Terra system. Rock avalanches within craters are widespread, but no significant large landslides have been found at latitudes higher than 40°S and 46°N. The magnitude-frequency distribution follows a power-law with scaling exponent ranging between 1.02 and 1.57, for the entire dataset, and varies according to the geomorphological settings, the landslide typology, and mobility. A volume-area power law relationship (exponent: 1.12-1.24) is proposed, based on the reconstruction of 222 landslide geometries, and compared to those for similar terrestrial landslides (1.39). Similarities with respect to terrestrial landslide, distribution with respect to impact craters and impact energy, and cryosphere extent are also discussed.

Vertical gravimeter array observations and their performance in groundwater level monitoring

Thu, 03/01/2018 - 20:01
Abstract

The gravitational effects of the atmosphere and subsurface water are significant obstacles to observing gravity variations on the sub-μGal (1 μGal = 10 nm/s2) scale. The goal of this study is to detect changes in gravity that are caused by mass redistributions deep underground related to seismological phenomena by reducing environmental gravity effects using multiple gravimeters below- and aboveground, which we term a “vertical gravimeter array”. Based on an evaluation of the responses to atmospheric effects and rainfall events identified in observations made with individual relative gravimeters, the vertical gravimeter array succeeds in stacking the target signals from deep underground and in reducing errors due to rainfall or free groundwater and atmospheric effects. To enable accurate interpretation, we introduce a physical approach that is based on attraction and loading deformation effects for atmospheric reduction using state-of-the-art gridded weather data products. Changes in the water levels of confined groundwater can be regarded as a signal from deep underground, and a response coefficient of approximately −15 μGal/m was obtained. In addition, the response coefficient of the free groundwater level was determined to be approximately 5 μGal/m. Such array observations are expected to contribute to monitoring crustal activity and hydrological studies.

Issue Information

Sat, 02/17/2018 - 09:58

No abstract is available for this article.

The Impacts of Bias in Cloud-Radiation-Dynamics Interactions on Central Pacific Seasonal and El Niño Simulations in Contemporary GCMs

Sun, 02/04/2018 - 05:07
Abstract

Most of the global climate models (GCMs) in the Coupled Model Intercomparison Project, phase 5 do not include precipitating ice (aka falling snow) in their radiation calculations. We examine the importance of the radiative effects of precipitating ice on simulated surface wind stress and sea surface temperatures (SSTs) in terms of seasonal variation and in the evolution of central Pacific El Niño (CP-El Niño) events. Using controlled simulations with the CESM1 model, we show that the exclusion of precipitating ice radiative effects generates a persistent excessive upper-level radiative cooling and an increasingly unstable atmosphere over convective regions such as the western Pacific and tropical convergence zones. The invigorated convection leads to persistent anomalous low-level outflows which weaken the easterly trade winds, reducing upper-ocean mixing and leading to a positive SST bias in the model mean state. In CP-El Niño events, this means that outflow from the modeled convection in the central Pacific reduces winds to the east, allowing unrealistic eastward propagation of warm SST anomalies following the peak in CP-El Niño activity. Including the radiative effects of precipitating ice reduces these model biases and improves the simulated life cycle of the CP-El Niño. Improved simulations of present-day tropical seasonal variations and CP-El Niño events would increase the confidence in simulating their future behavior.

High Angular Resolution Measurements of the Anisotropy of Reflectance of Sea Ice and Snow

Wed, 01/31/2018 - 17:02

We introduce a new method to determine the anisotropy of reflectance of sea ice and snow at spatial scales from 1 m2 to 80 m2 using a multispectral circular fish-eye radiance camera (CE600). The CE600 allows measuring radiance simultaneously in all directions of a hemisphere at a 1° angular resolution. The spectral characteristics of the reflectance and its dependency on illumination conditions obtained from the camera are compared to those obtained with a hyperspectral field spectroradiometer manufactured by Analytical Spectral Device, Inc. (ASD). Results confirm the potential of the CE600, with the suggested measurement setup and data processing, to measure commensurable sea ice and snow hemispherical-directional reflectance factor, HDRF, values. Compared to the ASD, the reflectance anisotropy measured with the CE600 provides much higher resolution in terms of directional reflectance (N = 16,020). The hyperangular resolution allows detecting features that were overlooked using the ASD due to its limited number of measurement angles (N = 25). This data set of HDRF further documents variations in the anisotropy of the reflectance of snow and ice with the geometry of observation and illumination conditions and its spectral and spatial scale dependency. Finally, in order to reproduce the hyperangular CE600 reflectance measurements over the entire 400–900 nm spectral range, a regression-based method is proposed to combine the ASD and CE600 measurements. Results confirm that both instruments may be used in synergy to construct a hyperangular and hyperspectral snow and ice reflectance anisotropy data set.

Modelling air pollution, climate and health data using Bayesian Networks: a case study of the English regions

Fri, 01/26/2018 - 06:00

The link between pollution and health is commonly explored by trying to identify the dominant cause of pollution and its most significant effect on health outcomes. The use of multivariate features to describe exposure is less explored because investigating a large domain of scenarios is theoretically (i.e. interpretation of results) and technically (i.e. computational effort) challenging. In this work we explore the use of Bayesian Networks with a multivariate approach to identify the probabilistic dependence structure of the environment-health nexus. This consists of environmental factors (topography, climate), exposure levels (concentration of outdoor air pollutants) and health outcomes (mortality rates). The information is collated with regard to a data-rich study area: the English regions (United Kingdom), which incorporate environmental types that are different in character from urban to rural. We implemented a reproducible workflow in the the R programming language to collate environment-health data and analyze almost 50 millions of observations making use of a graphical model (Bayesian Network) and Big Data technologies. Results show that for pollution and weather variables the model tests well in sample, but also has good predictive power when tested out of sample. This is facilitated by a training/testing split in the data along time and space dimension and suggests that the model generalises well to new regions and time periods.

Negative Aerosol-Cloud re Relationship From Aircraft Observations Over Hebei, China

Thu, 01/25/2018 - 04:50
Abstract

Using six flights observations in September 2015 over Hebei, China, this study shows a robust negative aerosol-cloud droplet effective radius (re) relationship for liquid clouds, which is different from previous studies that found positive aerosol-cloud re relationship over East China using satellite observations. A total of 27 cloud samples was analyzed with the classification of clean and polluted conditions using lower and upper 1/3 aerosol concentration at 200 m below the cloud bases. By normalizing the profiles of cloud droplet re, we found significant smaller values under polluted than under clean condition at most heights. Moreover, the averaged profiles of cloud liquid water content (LWC) show larger values under polluted than clean conditions, indicating even stronger negative aerosol-cloud re relationship if LWC is kept constant. The droplet size distributions further demonstrate that more droplets concentrate within smaller size ranges under polluted conditions. Quantitatively, the aerosol-cloud interaction is found around 0.10–0.19 for the study region.

Detecting Upward Directed Charged Particle Fluxes in the Mars Science Laboratory Radiation Assessment Detector

Tue, 01/23/2018 - 09:58

The Mars Science Laboratory rover Curiosity, operating on the surface of Mars, is exposed to radiation fluxes from above and below. Galactic Cosmic Rays travel through the Martian atmosphere, producing a modified spectrum consisting of both primary and secondary particles at ground level. These particles produce an upward directed secondary particle spectrum as they interact with the Martian soil. Here we develop a method to distinguish the upward and downward directed particle fluxes in the Radiation Assessment Detector (RAD) instrument, verify it using data taken during the cruise to Mars, and apply it to data taken on the Martian surface. We use a combination of Geant4 and Planetocosmics modeling to find discrimination criteria for the flux directions. After developing models of the cruise phase and surface shielding conditions, we compare model-predicted values for the ratio of upward to downward flux with those found in RAD observation data. Given the quality of available information on Mars Science Laboratory spacecraft and rover composition, we find generally reasonable agreement between our models and RAD observation data. This demonstrates the feasibility of the method developed and tested here. We additionally note that the method can also be used to extend the measurement range and capabilities of the RAD instrument to higher energies.

Issue Information

Wed, 01/10/2018 - 17:27

No abstract is available for this article.

Spectral Performance and Calibration of the Suomi NPP OMPS Nadir Profiler Sensor

Tue, 12/26/2017 - 14:50
Abstract

The Ozone Mapping and Profiler Suite (OMPS) is one of five instruments on board the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. As part of OMPS, the Nadir Profiler (NP) spectrometer measures Earth's albedo in ultraviolet wavelengths from 250 to 310 nm to profile Earth atmospheric ozone concentration. Since launch in 2011, many changes in the NP radiometric and spectrometric calibration have been made to improve sensor data quality. The most challenging issue is to characterize instrument on-orbit spectral calibration and to maintain a stable spectral performance to meet sensor design criteria. Validation of the NP sensor data found an average of 3–5% error in the sensor albedo measurements that exceeded 2% requirement, creating 1–2% uncertainty in ozone profile. Data analysis attributes the error to prelaunch calibration uncertainty, ground-to-orbit dichroic changes, and on-orbit detector wavelength registration drifts. A recent update of calibration significantly improved spectral wavelength knowledge as well as the accuracy of the measured solar spectra. As a result, the wavelength-dependent albedo error is significantly reduced and generally meets the radiometric uncertainty requirement of 2%.

Comparison Between Regularized Optimization Algorithms for Tomographic Reconstruction of Plume Cross Sections in the Atmosphere

Fri, 12/22/2017 - 07:41
Abstract

We analyze and compare two approaches for the tomographic reconstruction of trace gas distributions in the atmosphere, adapted to differential optical absorption spectroscopy (DOAS) applications. The first approach performs the inversion by solving a regularized least squares problem. Regularization is required because the retrieval of the distribution from a limited set of measurements is an ill-posed problem. This approach does not consider the nonnegativity of the trace gas concentrations. The second approach is a new proposal that solves an optimization problem with the Laplacian of the solution as the regularization term. This approach enables the possibility of adding the nonnegativity constraint to the solution. The algorithm here is stated as an instance of a convex optimization problem and can numerically be solved using, for example, the CVX package. We test both approaches on reconstructions of simulated gas distributions and different experimental configurations applicable to Multi-Axis DOAS and multispectral imaging measurements. From the results, we can then determine a set of reconstruction parameters appropriate to real plume measurements.

The Challenge of Atmospheric Data Assimilation on Mars

Tue, 12/19/2017 - 05:06

Data assimilation is carried out for the Martian atmosphere with the Mars Climate Sounder (MCS) retrievals of temperature, dust, and ice. It is performed for the period Ls = 180° to Ls = 320° of Mars Year 29 with the Local Ensemble Transform Kalman Filter scheme and the Laboratoire de Météorologie Dynamique (LMD) Mars Global Climate Model (GCM). In order to deal with the forcings of aerosols (dust and water ice) on atmospheric temperatures, a framework is given for multivariate analysis. It consists of assimilating a GCM variable with the help of another GCM variable that can be more easily related to an observation. Despite encouraging results with this method, data assimilation is found to be intrinsically different for Mars and more challenging, due to the Martian atmosphere being less chaotic and exhibiting more global features than on Earth. This is reflected in the three main issues met when achieving various data assimilation experiments: (1) temperature assimilation strongly forces the GCM away from its free-running state, due to the difficulty of assimilating global atmospheric thermal tides; (2) because of model bias, assimilation of airborne dust is not able to reproduce the vertical diurnal variations of dust observed by MCS, and not present in the GCM; and (3) water ice clouds are nearly impossible to assimilate due to the difficulty to assimilate temperature to a sufficient precision. Overall, further improvements of Martian data assimilation would require an assimilation that goes beyond the local scale and more realism of the GCM, especially for aerosols and thermal tides.

Issue Information

Mon, 12/11/2017 - 18:30

No abstract is available for this article.

AuroraWatch UK: An Automated Aurora Alert System

Fri, 12/08/2017 - 08:36

The AuroraWatch UK aurora alert service uses a network of magnetometers from across the United Kingdom to measure the disturbance in the Earth's magnetic field caused by the aurora borealis (northern lights). The service has been measuring disturbances in the Earth's magnetic field from the UK and issuing auroral visibility alerts to its subscribers, since September 2000. These alerts have four levels, corresponding to the magnitude of disturbance measured, which indicate from where in the UK an auroral display might be seen. In the following, we describe the AuroraWatch UK system in detail and reprocess the historical magnetometer data using the current alert algorithm to compile an activity database. This data set is composed of over 150,000 h (99.94% data availability) of magnetic disturbance measurements, including nearly 9,000 h of enhanced geomagnetic activity.

Viking-2 Seismometer Measurements on Mars: PDS Data Archive and Meteorological Applications

Tue, 11/28/2017 - 09:34
Abstract

A data product has been generated and archived on the NASA Planetary Data System (Geosciences Node), which presents the seismometer readings of Viking Lander 2 in an easy-to-access form, for both the raw (“high rate”) waveform records and the compressed (“event mode”) amplitude and frequency records. In addition to the records themselves, a separate summary file for each instrument mode lists key statistics of each record together with the meteorological measurements made closest in time to the seismic record. This juxtaposition facilitates correlation of the seismometer instrument response to different meteorological conditions, or the selection of seismic data during which wind disturbances can be expected to be small. We summarize data quality issues and also discuss lander-generated seismic signals, due to operation of the sampling arm or other systems, which may be of interest for prospective missions to other bodies. We review wind-seismic correlation, the “Martian solar day (sol) 80” candidate seismic event, and identify the seismic signature of a probable dust devil vortex on sol 482 : the seismometer data allow an estimate of the peak wind, occurring between coarsely spaced meteorology measurements. We present code to generate the plots in this paper to illustrate use of the data product.

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