Wind-Stress Dust Lifting in a Mars Global Circulation Model: Representation across Resolutions

The formation of Martian dust storms is believed to be driven by dust lifting by near-surface wind stress (NSWS). Accurately representing this dust lifting within Mars Global Circulation Models (MGCMs) is important in order to gain a full understanding of the Martian dust storm cycle. Parameterisations of dust lifting by NSWS exist within several MGCMs; implementations differ but they all follow a similar design, so progress within one model is relevant to the entire field. Few studies have explored in detail how the results of these parameterisations can be affected by changing the horizontal resolution of the model. An accurate parameterisation of dust lifting by NSWS will lift a representative dust mass, reproducing characteristic dust optical depths in the atmosphere. The geographical distribution of the dust lifting by NSWS will also change throughout the year, affecting patterns of dust storm formation and development. Currently, suitable values for dust lifting parameters must be identified at every new model resolution. Resolutions of ~5° latitude x ~5° longitude are often used to model the Martian climate, as thermal tides and long-term weather patterns can be well represented at this resolution. However, smaller scale phenomena (such as near-surface winds driven by local topography) cannot be accurately depicted at this resolution. We use the LMD-UK MGCM to complete multi-year simulations across multiple model resolutions. Our experiments range from ‘low’ resolution ~5° lat x ~5° lon to ‘high’ resolution ~1° lat x ~1° lon. In experiments with fixed, constant lifting parameters, we find that higher resolution simulations lift more dust, but that this trend is asymptotic. At low resolutions, dust lifting increases proportionately with the increase in number of horizontal gridboxes. However, at high resolutions, doubling the number of gridboxes results only in a 30% increase in the total dust mass lifted. Geographical and temporal distributions of dust lifting are investigated, as well as the total dust lifted, in order to assess the optimum parameters for each resolution, and to develop a calibration scheme for this dust lifting across model resolutions. The scheme is verified through comparison with spacecraft observations of dust optical depths and dust storm locations

How Do Martian Dust Devils Vary Throughout the Sol?

Dust devils are vortices of air made visible by entrained dust particles. Dust devils have been observed on Earth and captured in many Mars lander and orbiter images. Martian dust devils may be important to the global climate and are parameterised within Mars Global Circulation Models (MGCMs). We show that the dust devil parameterisation in use within most MGCMs results in an unexpectedly high level of dust devil activity during morning hours. In contrast to expectations, based on the observed behaviour of terrestrial dust devils and the diurnal maximum thermal contrast at the surface, we find that large areas of the modelled Martian surface experience dust devil activity during the morning as well as in the afternoon, and that many locations experience a peak in dust devil activity before mid-sol. Using the UK MGCM, we study the amount of surface dust lifted by dust devils throughout the diurnal cycle as a proxy for the level of dust devil activity occurring. We compare the diurnal variation in dust devil activity with the diurnal variation of the variables included in the dust devil parameterisation. We find that the diurnal variation in dust devil activity is strongly modulated by near-surface wind speeds. Within the range of daylight hours, higher wind speeds tend to produce more dust devil activity, rather than the activity simply being governed by the availability of heat at the planet's surface, which peaks in early afternoon. We compare our results with observations of Martian dust devil timings and obtain a good match with the majority of surface-based surveys. We do not find such a good match with orbital observations, but these data tend to be biased in their temporal coverage. We propose that the generally accepted description of dust devil behaviour on Mars is incomplete, and that theories of dust devil formation may need to be modified specifically for the Martian environment. Further dust devil observations are required to support any such modifications

Imagining the Thames: conceptions and functions of the river in the fiction of Charles Dickens

This thesis examines Dickens‟s uses of images of the river throughout his fiction, and also in the early sketches, the reprinted pieces from Household Words and The Uncommercial Traveller. The river concerned is usually but not exclusively the Thames, usually but not exclusively in London. The thesis offers some practical evidence to account for the powerful influence of the Thames upon Dickens‟s imagination and shows how he conceives of it both within existing frames of reference and in some distinctively Dickensian ways. It considers how Dickens‟s representations of the river play into the cult of the picturesque which emerged at the end of the eighteenth century, and into the tradition which sees it as a symbolic conduit of the empire. It goes on to consider his use of the river as a boundary, the consequent importance of river crossings in his work, and his conception of the riparian space as a liminal one. It then explores a distinctive scheme of discourse which uses the river to represent rebellious forces beyond the control of human agency and shows how this reflects the sense of spiritual threat which is to be found in some of the other, albeit rare, depictions of nature to be found in his writing. It then shows how Dickens uses the river symbolically to express ideas about death and rebirth, together with the loss of and changes in identity, and how he draws on a scheme of distinctively Christian iconography to do so. Finally it shows how he uses it to create and represent an underworld for London, using tropes of epic founded on classical models. The thesis concludes that, in its use of natural forces to signify social ones, Dickens‟s writing about the river serves to amplify his conception of stratification in Victorian society and adds weight to the socially conservative political stance which is known to be present in his world view

Facilitating Humanitarian Access to Pharmaceutical and Agricultural Innovation

Calls for intellectual property licensing strategies in the pharmaceutical and agricultural sectors that promote humanitarian access to product innovations for the benefit of the disadvantaged. Includes profiles of successful and promising strategies

Aberrant Wing Pigmentation in \u3ci\u3eLibellula Luctuosa\u3c/i\u3e Specimens From Ohio

Over the past few years we obtained three female Libellula luctuosa specimens, all collected in northeast Ohio, which exhibited unusually reduced wing pigmentation. The individuals were extremely difficult to identify as most keys rely heavily upon wing pigmentation for identification of many Libellula species. A description of this aberrant wing pigmentation and a photograph are provided

High-Density Repository Storage: An Evaluation and Comparison of Costs at Harvard and OCLC Is Repository Storage Affordable?

Intervention à la 33e conférence générale annuelle de la Ligue des bibliothèques européennes de recherche (Liber)