The circulatory impact of dust from dust profile assimilation

We present results from a reanalysis of temperatures, dust columns and dust vertical profiles focussing on the assimilation, distribution and transport of dust in the martian atmosphere. The assimilation of dust vertical information in particular is a valuable technique which has been shown to be of vital importance to a successful assimilation of the martian atmosphere, with the vertical representation of the dust distribution having a critical effect on assimilation results generally. Atmospheric dust is a key driver of the martian circulation. Dust-induced heating and cooling is a potential feedback mechanism for dust lifting, for example, and can modify the circulation to either enhance or suppress dust storm activity. Accurately representing its complex spatial and temporal distribution is therefore crucial for understanding Mars’ atmospheric dynamics and transport

Planetary wave reanalysis using satellite data

A key motivation to use data assimilation for plane-tary science is in order to recover information about day-to-day atmospheric variability, or ‘weather’. Whilst there is no immediate need for a regular weather forecast in most planetary science, data assimilation offers the prospect of a systematic rea-nalysis of past and present spacecraft data. This is especially valuable when, as is often the case, a planet is being observed from only one or two orbital platforms at any one time and synoptic-scale weather system may translate and change signifi-cantly between satellite passes. Observations are often sparse and incomplete. This leads to problems of aliasing and potential ambiguity in a convention-al data analysis

Investigating the Role of Advection Processes in Improved Martian Dust Assimilation Techniques for ExoMars

Mineral dust is a key component in the atmosphere of Mars, and understanding its properties and behaviour is therefore key for planning and performing future activity on the planet. Data assimilation is a technique for combining observations with an atmospheric model, in this case the LMD-UK Mars General Circulation Model (MGCM). We describe its benefits and previous work in Martian data assimilation, and demonstrate its utility by examining a regional dust event in Mars Year 26 using Thermal Emission Spectrometer (TES) dust optical depth observations. We set out aims to improve upon current dust assimilation techniques, specifically regarding the advection of dust within the assimilation, in preparation for forthcoming high-resolution dust observations from the ExoMars Trace Gas Orbiter (TGO) and its NOMAD spectrometer

Measuring fast electron spectra and laser absorption in relativistic laser-solid interactions using differential bremsstrahlung photon detectors

A photon detector suitable for the measurement of bremsstrahlung spectra generated in relativistically-intense laser-solid interactions is described. The Monte Carlo techniques used to back-out the fast electron spectrum and laser energy absorbed into fast electrons are detailed. A relativistically-intense laser-solid experiment using frequency doubled laser light is used to demonstrate the effective operation of the detector. The experimental data was interpreted using the 3-spatial-dimension Monte Carlo code MCNPX (Pelowitz 2008), and the fast electron temperature found to be 125 keV

Soil moisture, stressed vegetation and the spatial structure of soil erosion in a high latitude rangeland

Funding: Research was supported by a NERC PhD studentship (ref: NE/L002558/) to Polly Thompson and a World-Leading Scholarship, funded by St Leonard’s Postgraduate College, University of St Andrews, to Georg Kodl.Soil erosion has been a persistent problem in high-latitude regions and may worsen as climate change unfolds and encourages increased anthropogenic exploitation. We propose that soil moisture is likely to shape future erosion trends, as moisture stress reduces the capacity of vegetation cover to retard erosive processes. However, the spatial variability of soil moisture in high-latitude soils—and the ways in which this variability drives the spatial distribution of erosion features—is poorly understood. We addressed this knowledge gap with a study of andosol erosion in southern Iceland. Our study used a combination of high-resolution (10 m from eroded terrain. We found lower moisture availability close to existing erosion features: mean volumetric soil moisture content varied from 17% (proximal to erosion patch) to 36% (distal to erosion patch). We also found that variability in soil moisture decreased with distance from eroded areas: the coefficient of variation (CV) in soil moisture varied from 0.33 (proximal to erosion patch) to 0.13 (distal to erosion). Our findings indicate that the margins of erosion patches have a stressful soil environment due to exposure to the atmosphere. The vegetation in these locations grows less vigorously, and the exposed soil becomes more vulnerable to erosion, leading to erosion patch expansion and coalescence. If these conditions hold more generally, they may represent a feedback mechanism that facilitates the lateral propagation of soil erosion in high-latitude regions.Publisher PDFPeer reviewe

Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator

We show that the properties of the electron beam and bright x-rays produced by a laser wakefield accelerator can be predicted if the distance over which the laser self-focuses and compresses prior to self-injection is taken into account. A model based on oscillations of the beam inside a plasma bubble shows that performance is optimised when the plasma length is matched to the laser depletion length. With a 200~TW laser pulse this results in an x-ray beam with median photon energy of \unit[20]{keV}, $> 6\times 10^{8}$ photons above \unit[1]{keV} per shot and a peak brightness of \unit[3 \times 10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure