Gravity wave generation and breaking observed with radiosondes at Ushuaia (Argentina)

We examine 25 high resolution radiosondes that were launched at Ushuaia (54.8S) during October-December, 1995. Gravity wave activity in the lower stratosphere from 10 km to 24 km presents a high variability which appears to be related to the polar jet position. In particular, the wave activity maximum is found when the polar jet is located above Ushuaia. The enhancement of gravity wave activity is ascribed to a conjuntion of gravity wave generation and Doppler-shifting . Two high wave activity cases are examined. They present inertio-gravity waves (IGW) with periods of 8-12h and 12-14h. Profiles of the Richardson number (Ri) present some patches where Ri descends bellow one quarter mainly induced by wave shear. These patches are identified as regions where IGWs are breaking. The possibility of gravity wave generation by Kelvin-Helmholtz instability and geostrophic adjustment are evaluated using the synoptic situation from ECMWF analyses.Pages: 627-63

Deep convection east of the Andes Cordillera: four hailstorm cases

An analysis of four cases of severe hailstorms that occurred east of the Andes Cordillera in the northern part of Argentina is presented in this article. Analysed and observed data, as well as mesoscale model integrations, are used to evidentiate the underlying physical mechanism. The formation of heavy hailstones is the consequence of intense deep moist convection, with sufficiently high updraft speed to produce super-cooled water. The presence of warm and moist air is found. It appears to be a necessary but not sufficient condition to generate such intense convection. Convergence of moist enthalpy near the ground is also found. The passage of a cold front creates instabilities and causes upward motion on the warm side of the front, facilitating the development of deep convection. In some cases, low-level flow around a mountain creates wind convergence on the lee side, associated with lifting of air parcels. Although mountain waves are very frequent in the region, they do not appear determinant for the triggering of convection in the cases studied. It must be stressed that the results of this study are the consequences of the climatology of the region and cannot be trivially extrapolated to other regions

Three-dimensional properties of Andes mountain waves observed by satellite: A case study

International audienceThe southern Andes region has been clearly identified in previous satellite and balloon observations and in global models as a "hot spot" of small-scale gravity wave activity, with monthly mean momentum fluxes exceeding 10 times background values in fall, winter, and spring seasons. This makes this region a focus of interest for global circulation and climate studies. We analyze a case study on 8 May 2006, combining observations from the Atmospheric Infrared Sounder instrument on the Aqua satellite and the High Resolution Dynamics Limb Sounder instrument of the Aura satellite to form a three-dimensional picture of the wave field. The observations show a widespread wave pattern over the southern Andes extending eastward over the south Atlantic. Simulations with the Weather Research Forecasting model clearly identify the waves as orographic in origin, but the observed wave pattern is far from the simple two-dimensional wave field forced by steady flow over a mountain ridge. The morphology of the pattern is consistent with three-dimensional linear theoretical calculations of downstream propagation and latitudinal focusing of mountain waves into the stratospheric jet. The observations confirm the importance of this process in the stratosphere, and we find the process also occurring in the global analysis and forecasts from the European Centre for Medium-Range Weather Forecasting. Our analysis evaluates some strengths and weaknesses of current orographic wave drag parameterizations in global models and the relevance of parameterization assumptions in global models with high resolution. Copyright 2011 by the American Geophysical Union

Global Survey of Outcomes of Neurocritical Care Patients: Analysis of the PRINCE Study Part 2

BACKGROUND: Neurocritical care is devoted to the care of critically ill patients with acute neurological or neurosurgical emergencies. There is limited information regarding epidemiological data, disease characteristics, variability of clinical care, and in-hospital mortality of neurocritically ill patients worldwide. We addressed these issues in the Point PRevalence In Neurocritical CarE (PRINCE) study, a prospective, cross-sectional, observational study. METHODS: We recruited patients from various intensive care units (ICUs) admitted on a pre-specified date, and the investigators recorded specific clinical care activities they performed on the subjects during their first 7 days of admission or discharge (whichever came first) from their ICUs and at hospital discharge. In this manuscript, we analyzed the final data set of the study that included patient admission characteristics, disease type and severity, ICU resources, ICU and hospital length of stay, and in-hospital mortality. We present descriptive statistics to summarize data from the case report form. We tested differences between geographically grouped data using parametric and nonparametric testing as appropriate. We used a multivariable logistic regression model to evaluate factors associated with in-hospital mortality. RESULTS: We analyzed data from 1545 patients admitted to 147 participating sites from 31 countries of which most were from North America (69%, N = 1063). Globally, there was variability in patient characteristics, admission diagnosis, ICU treatment team and resource allocation, and in-hospital mortality. Seventy-three percent of the participating centers were academic, and the most common admitting diagnosis was subarachnoid hemorrhage (13%). The majority of patients were male (59%), a half of whom had at least two comorbidities, and median Glasgow Coma Scale (GCS) of 13. Factors associated with in-hospital mortality included age (OR 1.03; 95% CI, 1.02 to 1.04); lower GCS (OR 1.20; 95% CI, 1.14 to 1.16 for every point reduction in GCS); pupillary reactivity (OR 1.8; 95% CI, 1.09 to 3.23 for bilateral unreactive pupils); admission source (emergency room versus direct admission [OR 2.2; 95% CI, 1.3 to 3.75]; admission from a general ward versus direct admission [OR 5.85; 95% CI, 2.75 to 12.45; and admission from another ICU versus direct admission [OR 3.34; 95% CI, 1.27 to 8.8]); and the absence of a dedicated neurocritical care unit (NCCU) (OR 1.7; 95% CI, 1.04 to 2.47). CONCLUSION: PRINCE is the first study to evaluate care patterns of neurocritical patients worldwide. The data suggest that there is a wide variability in clinical care resources and patient characteristics. Neurological severity of illness and the absence of a dedicated NCCU are independent predictors of in-patient mortality.status: publishe