The Effects of the Laurentide Ice Sheet on North American Climate during the Last Glacial Maximum

A climate model, consisting of an atmospheric general circulation model coupled with a simple model of the oceanic mixed layer, is used to investigate the effects of the continental ice distribution of the last glacial maximum (LGM) on North American climate. This model has previously been used to simulate the LGM climate, producing temperature changes reasonably in agreement with paleoclimatic data. The LGM distribution of continental ice according to the maximum reconstruction of HUGHES et al. (1981) is used as input to the model. In response to the incorporation of the expanded continental ice of the LGM, the model produces major changes in the climate of North America. The ice sheet exerts an orographic effect on the tropospheric flow, resulting in a splitting of the midlatitude westerlies in all seasons but summer. Winter temperatures are greatly reduced over a wide region south of the Laurentide ice sheet, although summer cooling is less extensive. An area of reduced soil moisture develops in the interior of North America just south of the ice margin. At the same time, precipitation increases in a belt extending from the extreme southeastern portion of the ice sheet eastward into the North Atlantic. Some of these findings are similar to paleoclimatic inferences based on geological evidence.Un modèle climatique, composé d'un modèle de circulation atmosphérique général associé à un modèle simple de la couche océanique mixte, a servi à étudier l'influence de la répartition des glaciers continentaux sur le climat de l'Amérique du Nord au dernier pléniglaciaire. Ce modèle avait déjà servi pour simuler le climat au dernier pléniglaciaire; il a montré des changements de températures concordant assez bien avec les données paléoclimatiques. La répartition des glaces continentales pendant le pléniglaciaire selon l'hypothèse d'extension maximale de HUGHES et al. (1981) a servi à la modélisation. En réponse à l'incorporation des données de cette hypothèse, le modèle fait voir des changements majeurs dans le climat de l'Amérique du Nord. La présence de la calotte glaciaire fait ressortir l'influence de l'orographie sur le flux troposphérique qui se concrétise par une séparation des vents d'ouest aux latitudes moyennes durant toutes les saisons, sauf l'été. Les températures hivernales s'abaissent substantiellement dans une vaste région située au sud de la calotte laurentidienne, bien que le refroidissement soit moindre durant l'été. Une zone sèche se développe immédiatement au sud de la marge glaciaire. Au même moment, les précipitations augmentent dans la région qui s'étend de l'extrémité sud-est de la calotte glaciaire jusque dans l'Atlantique Nord, à l'est. Certains de ces résultats sur la nature du paléoclimat sont similaires aux déductions que les données géologiques ont inspirées.Um die Auswirkungen der kontinentalen Eisverbreitung im jüngsten glazialen Maximum auf das nordamerikanische Klima zu erforschen, wird ein Klima-Modell benutzt. das aus einem Modell der Hauptluftströmung in Verbindung mit einem einfachen Modell der gemischten ozeanischen Schicht besteht. Frùher wurde dieses Modell benutzt, um das Klima im jüngsten glazialen Maximum zu simulieren. Die Ergebnisse haben Temperaturschwankungen ergeben, die einigermapen genau mit den paleoklimatischen Daten übereinstimmten. Ausgegangen wurde bei dem Modell von der Verteilung des kontinentalen Eises im jüngsten glazialen Maximum entsprechend der Maximum-Rekonstruktion von HUGHES et al. (1981). AIs Antwort auf die Einverleibung des ausgedehnten kontinentalen Eises im jüngsten glazialen Maximum produziert das Modell bedeutende Veränderungen im nordamerikanischen Klima. Die Eisdecke übt eine orographische Wirkung auf die troposphärische Luftströmung aus, was zu einer Aufsplitterung der westlichen Winde mittlerer Breite in alien Jahreszeiten auBer im Sommer führt. Die Winter-Temperaturen sinken stark in einem weiten Gebiet südlich der laurentischen Eisdecke, während die sommerliche Abkühlung weniger stark ausfällt. Im Innern Nordamerikas südlich der Eisgrenze entwickelt sich ein Gebiet verringerter Bodenfeuchtigkeit. Gleichzeitig nehmen die Niederschläge innerhalb eines Gürtels zu, der von dem äupersten südöstlichen Teil der Eisdecke ostwärts in den Nordatlantik reicht. Einige dieser Ergebnisse decken sich mit paleoklimatischen Folgerungen, die sich auf geologische Nachweise stützen

Destabilization of the thermohaline circulation by transient perturbations to the hydrological cycle

We reconsider the problem of the stability of the thermohaline circulation as described by a two-dimensional Boussinesq model with mixed boundary conditions. We determine how the stability properties of the system depend on the intensity of the hydrological cycle. We define a two-dimensional parameters' space descriptive of the hydrology of the system and determine, by considering suitable quasi-static perturbations, a bounded region where multiple equilibria of the system are realized. We then focus on how the response of the system to finite-amplitude surface freshwater forcings depends on their rate of increase. We show that it is possible to define a robust separation between slow and fast regimes of forcing. Such separation is obtained by singling out an estimate of the critical growth rate for the anomalous forcing, which can be related to the characteristic advective time scale of the system.Comment: 37 pages, 8 figures, submitted to Clim. Dy

Distribuição de formações pioneiras no Pantanal brasileiro.

Em regiões alagáveis como o Pantanal, a alternância de períodos secos e cheios favorece o aparecimento de vegetação sob influência fluvial ou lacustre - as pioneiras. Via de regra esta vegetação geralmente está associada às áreas inundadas ou brejos próximos aos rios da região. O presente trabalho tem como objetivo construir um mapa da distribuição da vegetação pioneira no Pantanal brasileiro. Utilizaram-se dados levantados pelo projeto Probio-Pantanal, que foram trabalhados e cruzados por meio do programa Spring. A vegetação pioneira se localiza em faixas por todo lado Oeste do Pantanal, e ainda com algumas manchas no nordeste e sudeste, totalizando 5.212 km², ocupando 3,76% da área da planície ou 3,46% quando se considera a área do Bioma. As Formações Pioneiras foram encontradas sobre solos com pouca capacidade de drenagem e próximo aos principais rios pantaneiros. Desta forma, foi possível localizar a vegetação pioneira no Pantanal brasileiro, e quais fatores contribuem para seu aparecimento.Geopantanal 2010

Estudo da expansão de áreas de cana-de-açúcar na Bacia do Alto Paraguai.

O presente trabalho tem por objetivo analisar a expansão da área cultivada com cana-de-açúcar nessa bacia, no período de 2005 a 2009, e quais fisionomias foram convertidas

Neutron Scattering Study of Temperature-Concentration Phase Diagram of (Cu1-xMgx)GeO3

In doped CuGeO3 systems, such as (Cu1-xZnx)GeO3 and Cu(Ge1-xSix)O3, the spin-Peierls (SP) ordering (T<Tsp) coexists with the antiferromagnetic (AF) phase (T<TN<Tsp). Tsp decreases while TN increases with increasing x in low doping region. For higher x, however, the SP state disappears and only the AF state remains. These features are common for all the doped CuGeO3 systems so far studied, indicating the existence of universal T-x phase diagram. Recently, Masuda et al. carried out comprehensive magnetic susceptibility (chi) measurements of (Cu1-xMgx)GeO3, in which doping concentration can be controlled significantly better than the Zn doped systems. They found that TN suddenly jumps from 3.43 to 3.98K at the critical concentration xc sim 0.023 and that a drop in chi corresponding to the SP ordering also disappears at x>xc. They thus concluded that there is a compositional phase boundary between two distinct magnetic phases. To clarify the nature of two phases, we performed neutron-scattering measurements on (Cu1-xMgx)GeO3 single crystals with various x. Analysis of the data at fixed temperature points as a function of doping concentration has revealed sudden changes of order parameters at the critical concentration xc=0.027 +- 0.001. At finite temperatures below TN, the drastic increase of the AF moment takes place at xc. The spin-Peierls order parameter delta associated with lattice dimerization shows a precipitous decrease at all temperature below Tsp. However, it goes to zero above xc only at the low temperature limit.Comment: 9 pages, 9 figure

Volcanic forcing improves Atmosphere-Ocean Coupled General Circulation Model scaling performance

Recent Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations of the twentieth century climate, which account for anthropogenic and natural forcings, make it possible to study the origin of long-term temperature correlations found in the observed records. We study ensemble experiments performed with the NCAR PCM for 10 different historical scenarios, including no forcings, greenhouse gas, sulfate aerosol, ozone, solar, volcanic forcing and various combinations, such as it natural, anthropogenic and all forcings. We compare the scaling exponents characterizing the long-term correlations of the observed and simulated model data for 16 representative land stations and 16 sites in the Atlantic Ocean for these scenarios. We find that inclusion of volcanic forcing in the AOGCM considerably improves the PCM scaling behavior. The scenarios containing volcanic forcing are able to reproduce quite well the observed scaling exponents for the land with exponents around 0.65 independent of the station distance from the ocean. For the Atlantic Ocean, scenarios with the volcanic forcing slightly underestimate the observed persistence exhibiting an average exponent 0.74 instead of 0.85 for reconstructed data.Comment: 4 figure

The atmospheric response to a thermohaline circulation collapse: scaling relations for the Hadley circulation and the response in a coupled climate model

The response of the tropical atmosphere to a collapse of the thermohaline circulation (THC) is investigated by comparing two 5-member ensemble runs with a coupled climate model (CCM), the difference being that in one ensemble a hosing experiment was performed. An extension of the Held–Hou–Lindzen model for the Hadley circulation is developed to interpret the results. The forcing associated with a THC collapse is qualitatively similar to, but smaller in amplitude than, the solstitial shift from boreal summer to winter. This forcing results from reduced ocean heat transport creating an anomalous cross-equatorial SST gradient. The small amplitude of the forcing makes it possible to arrive at analytical expressions using standard perturbation theory. The theory predicts the latitudinal shift between the Northern Hemisphere (NH) and Southern Hemisphere (SH) Hadley cells, and the relative strength of the anomalous cross-equatorial Hadley cell compared to the solstitial cell. The poleward extent of the Hadley cells is controlled by other physics. In the NH the Hadley cell contracts, while zonal velocities increase and the subtropical jet shifts equatorward, whereas in the SH cell the opposite occurs. This behavior can be explained by assuming that the poleward extent of the Hadley cell is determined by baroclinic instability: it scales with the inverse of the isentropic slopes. Both theory and CCM results indicate that a THC collapse and changes in tropical circulation do not act in competition, as a possible explanation for abrupt climate change; they act in concert.<br/

A Cryptographic Moving-Knife Cake-Cutting Protocol

This paper proposes a cake-cutting protocol using cryptography when the cake is a heterogeneous good that is represented by an interval on a real line. Although the Dubins-Spanier moving-knife protocol with one knife achieves simple fairness, all players must execute the protocol synchronously. Thus, the protocol cannot be executed on asynchronous networks such as the Internet. We show that the moving-knife protocol can be executed asynchronously by a discrete protocol using a secure auction protocol. The number of cuts is n-1 where n is the number of players, which is the minimum.Comment: In Proceedings IWIGP 2012, arXiv:1202.422