1,720,958 research outputs found
The impact of topography and albedo on weather patterns and the location of the Martian South polar CO2 ice cap
Full text linkMeteorological and physical results from the second version of Global Mars Multiscale Model (GM3-v2) were used to investigate the impact of topography and albedo on the Martian southern polar CO2 ice cap. Analysis of the numerical simulations revealed significant differences in the horizontal and vertical cross sections of temperature when model was run for plain topography.
Wind streamlines from Ls= 20° (early southern fall) to Ls = 200° (early southern spring) for every one Ls have been analysed. Wind streamline pattern analysis shows there are two cyclonic circulations during southern winter; one around the Hellas basin (in the eastern hemisphere) and the second one around the Argyre basin (in the western hemisphere). However, between these two cyclonic cells, the pattern is anti-cyclonic.
Since the albedo map which is used in the model represents a mean state of albedo for all seasons of the planet, the albedo values have been modified in the polar regions to allow for the formation of the surface ice in the model. Also this modification will be very important in the water cycle simulation. As a second step in this work, the albedo values at the poles (mostly focusing on south polar regions) were modified for a better representation of the physical situation.
However, the seasonal carbon dioxide ice in the polar regions is presented in the surface ice simulation by the second version of Global Mars Multiscale Model, but it does not produce a permanent south CO2 ice cap, and so it must be modified in the physics code in order to capture the real physical and meteorological processes. The permanent south CO2 ice cap in the model can significantly improve the representation of south polar meteorology for example in predicted surface temperatures, surface pressures, horizontal and zonal winds over the south cap and also possible initiation of dust storms at south polar region during the southern summer period. In the final part to this thesis, the residual CO2 ice cap is simulated in the physics code
Dynamics of Jupiter’s equatorial zone: Instability analysis and a mechanism for Y-shaped structures
No full textInternational audienceJupiter's Equatorial Zone (EZ) is characterized by atmospheric dynamics influenced by strong zonal jets. Initially, we perform a linear stability analysis of two-layer geostrophic flows to explore the growth and evolution of instabilities associated with equatorial jets. Stability diagrams reveal that the most unstable baroclinic modes shift to lower wavenumbers with increasing zonal velocities, indicating sensitivity to the strength of the zonal wind. We show notable differences in phase velocities between barotropic and baroclinic jets. Phase portraits of the dynamic structures of various wave types, including barotropic and baroclinic Kelvin waves, Yanai waves, Rossby waves, and inertia-gravity waves, are illustrated in this analysis. Subsequently, we employ a two-layer moist convective Rotating Shallow Water (2mcRSW) model to investigate the nonlinear interactions between ammonia-driven convective processes in the shallow upper atmosphere and large-scale atmospheric features in Jupiter's EZ. We analyze the evolution of nonlinear instabilities in moist-convective flows by perturbing a background zonal velocity field with the most unstable mode. Findings include the amplification of cyclonic and anticyclonic vortices driven by moist convection at the boundaries of the zonal jets and the suppression of convective vortices in equatorial bright zones. This study underscores the role of moist convection in generating upper atmosphere cloud clusters and lightning patterns, as well as the chevron-shaped pattern observed on the poleward side of the zonal jets. Finally, we propose a novel mechanism for the formation of Y-shaped structures on Jupiter, driven by equatorial modons coupled with convectively baroclinic Kelvin waves (CCBCKWs). This mechanism suggests that Y-shaped structures result from large-scale localized heating in a diabatic environment, which, upon reaching a critical threshold of negative pressure or positive buoyancy anomaly, generates a hybrid structure. This hybrid structure consists of a quasi equatorial modon, a coherent dipolar structure, coupled with a CCBCKW that propagates eastward in a self-sustaining and self-propelled manner. Initially, the hybrid moves steadily eastward; however, the larger phase speed of the CCBCKW eventually leads to its detachment from the quasi equatorial modon. The lifetime of this coupled structure varies from interseasonal to seasonal timescales. Moist convection is a necessary condition for triggering the eastward-propagating structure
Torrential rainfall with severe flooding associated with a baroclinic disturbance on November 17, 2023, United Arab Emirates (UAE)
No full textInternational audienceThis work examines a severe weather event caused by a baroclinic disturbance with heavy rainfall and thunderstorms, which struck parts of the UAE and caused major flooding on November 17, 2023. A low-pressure trough extending from the Red Sea Trough (RST) towards the Eastern Mediterranean (EM) led to extreme flooding. The unique intensity of this heavy rainfall was correlated to midlatitude disturbance amplification even in the middle and upper tropospheric produced by RST. During the rain event, two intense moisture sources were injected into the region: one from the Indian Ocean, carried by southeasterly near-surface winds at 10m, and the other from the Red Sea and Equatorial Africa, transported at a mid-tropospheric level. A significant temperature gradient with ~8 °C difference in surface temperatures, particularly between the northern areas in contrast with the southern regions, and the wind shear formation over the northern parts of the study area initiated the baroclinicity structure in the borderlines of the cold front and thunderstorms. The findings also revealed an abnormal westerly jet stream intensification at 200 hPa, associated with a negative meridional wind anomaly, signaling the stretching of a Rossby wave over the study area during the heavy rainfall and flooding.</div
Aeolus 2.0's thermal rotating shallow water model: A new paradigm for simulating extreme heatwaves, westerly jet intensification, and more
No full textInternational audienceIn this study, we demonstrate the dynamical core and applicability of Aeolus 2.0, a moist-convective thermal rotating shallow water model of intermediate complexity, along with its novel bulk aerodynamic and moist-convective schemes, in capturing the effects of increased radiative forcing on zonal winds and heatwaves. Simulations reveal seasonal patterns in zonal wind, temperature, and energy anomalies under increased radiative forcing during the summer solstice, winter solstice, and equinoxes. Increased radiative forcing enhances mid-latitudinal temperatures during the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere, leading to increased zonal wind velocity in the affected hemisphere, especially in the subtropics, while decreasing it in the opposite hemisphere. This thermal forcing also reduces the zonal wind velocity of polar cyclones in the hemisphere experiencing increased radiative forcing. During the autumn equinox, zonal wind velocity diminishes in the Southern Hemisphere, while a similar reduction occurs in the Northern Hemisphere during the spring equinox. Heightened meridional gradients significantly influence the poleward displacement of atmospheric circulation, particularly during the summer (northward) and winter (southward) solstices. Poleward eddy heat fluxes persist across hemispheres, indicating a consistent response to external heating. Increased radiative forcing during the summer and winter solstices amplifies prolonged heatwaves across land and ocean, exceeding impacts observed during the spring and autumn equinoxes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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