Water vapor satellite products in the European Arctic: An inter-comparison against GNSS data.

The European Arctic is a region of high interest for climate change. Water vapor plays a fundamental role in global warming; therefore, high-quality water vapor monitoring is essential for assimilation in forecast simulations. The seven analyzed instruments on-board satellite platforms are: Atmospheric Infrared Sounder (AIRS), Global Ozone Monitoring Instrument 2 (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), SCanning Imaging Absorption Spectrometer for Atmospheric Carthography (SCIAMACHY) and Polarization and Directionality of the Earth's Reflectances (POLDER). The GNSS data from Ny-Ålesund are matched to satellite observations of IWV in a 30-min temporal window, and 100-km radius. Then, statistics and the distribution of satellite-ground differences under different conditions are studied. The correlation coefficient (R2) with ground-based measurements is about 0.7 for all products except OMI (R2=0.5), and MODIS NIR and POLDER (R2=0.3). OMI shows high bias and variability compared to the rest of products. RMSE values are of the order of 3 mm for all satellites, except OMI (7 mm) and POLDER (5 mm). Bias (MBE) is negligible for AIRS, close to +1.6 mm for GOME-2 and MODIS IR, +0.8 mm for MODIS NIR, +5.9 mm for OMI, -2.7 mm for POLDER and -1.2 mm for SCIAMCHY. All satellite products tend to overestimate small IWV values and underestimate large IWV values. Variability also increases with IWV. An underestimation of the satellite products and an increase on the variability is generally observed for large Solar Zenith Angle (SZA) values. Under cloudy conditions, underestimation and variability are increased. Seasonal behavior is driven by the typical cloud cover (CC), SZA, and IWV values. In summer, it is typical to find conditions with large IWV, small SZA and large CC values. Therefore, in summer months satellite products are more biased (either positively or negatively) and with more variability, but in relative terms they are less biased and exhibit less variability.

Comparison of integrated water vapor from GNSS and radiosounding at four GRUAN stations.

Integrated water vapor (IWV) data from Global Navigation Satellite Systems (GNSS) and radiosounding (RS) are compared over four sites (Lindenberg, Ny-Ålesund, Lauder and Sodankylä), which are part of the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN). Both datasets show an excellent agreement, with a high degree of correlation (R2 over 0.98). Dependences of GNSS-RS differences on several variables are studied in detail. Mean bias error (MBE) and standard deviation (SD) increase with IWV, but in relative term, these variables decrease as IWV increases. The dependence on solar zenith angle (SZA) is partially related to the distribution of IWV with SZA, but the increase of SD for low SZA could be associated with errors in the humidity sensor. Large surface pressures worsen performance, which could be due to the fact that low IWV is typically present in high pressure situations. Cloud cover shows a weak influence on the mentioned MBE and SD. The horizontal displacement of radiosondes generally causes SD to increase and MBE to decrease (increase without sign), as it could be expected. The results point out that GNSS measurements are useful to analyze performance to other instruments measuring IWV.

Validation of integrated water vapor from OMI satellite instrument against reference GPS data at the Iberian Peninsula.

This paper shows the validation of integrated water vapor (IWV) measurements retrieved from the Ozone Monitoring Instrument (OMI), using as reference nine ground-based GPS stations in the Iberian Peninsula. The study period covers from 2007 to 2009. The influence of two factors, - solar zenith angle (SZA) and IWV -, on OMI-GPS differences was studied in detail, as well as the seasonal dependence. The pseudomedian of the relative differences is -1 ± 1% and the inter-quartile range (IQR) is 41%. Linear regressions calculated over each station show an acceptable agreement (R2 up to 0.77). The OMI-GPS differences display a clear dependence on IWV values. Hence, OMI substantially overestimates the lower IWV data recorded by GPS (∼ 40%), while underestimates the higher IWV reference values (∼ 20%). In connection to this IWV dependence, the relative differences also show an evident SZA dependence when the whole range of IWV values are analyzed (OMI overestimates for high SZA values while underestimates for low values). Finally, the seasonal variation of the OMI-GPS differences is also associated with the strong IWV dependence found in this validation exercise.

Sensitivity of UV Erythemal Radiation to Total Ozone Changes under Different Sky Conditions: Results for Granada, Spain.

This study focuses on the analysis of the sensitivity of UV erythemal radiation (UVER) to variations in the total ozone column (TOC) under different sky conditions at Granada (southeastern Spain). The sensitivity is studied both in relative terms by means of the Radiation Amplification Factor (RAF) and in absolute terms using the Ozone Efficiency (OE). These two variables are determined for diverse sky conditions characterized by the cloud cover information given by a sky camera (in oktas) and the cloud optical depth (COD) estimated from global solar radiation measurements. As expected, in absolute terms, the TOC variations cause substantially smaller UVER changes during completely overcast situations than during cloud-free cases. For instance, the OE (SZA = 30°, TOC = 290 DU) decreases from 0.68 mW m(-2) per unit of TOC (0 oktas) to 0.50 mW m(-2) per unit of TOC (8 oktas). However, the opposite is observed when the analysis is performed in relative terms. Thus, the RAF (determined for SZA cases below 80°) increases from 1.1 for cloud-free cases (0 oktas) to 1.4 for completely overcast situations (8 oktas). This opposite behavior is also found when both RAF and OE are analyzed as functions of COD. Thus, while the OE strongly decreases with increasing COD, the RAF increases as COD increases.

Empirical evaluation of a simple analytical formula for the ultraviolet index.

This paper focuses on the estimation of the UV Index (UVI) for all sky conditions using a simple analytical parameterization involving three independent variables: the solar zenith angle, the total ozone column and the clearness index. Measurements of the UVI made at Badajoz and Cáceres (Southwestern Spain) from January 2006 to December 2007 are used to estimate optimal fitting parameters for the model formula, while measurements from January to December 2008 are used to show that the formula-based estimations have mean absolute errors lower than 6% and R(2) ca 0.99.

Variability in the diagnosis and management of patients with Alzheimer's disease and cerebrovascular disease: results from the GALATEA multicentre, observational study.

BACKGROUND AND OBJECTIVES: There is frequently a degree of variability among different types of dementia specialists in clinical practice in both the clinical diagnosis and the management of patients with Alzheimer's disease and cerebrovascular disease (CVD). This variability may have an adverse effect on the use of medical resources as well as on patients' well-being. The main objective of this study was to describe the current diagnosis and management of patients with Alzheimer's disease and CVD in Spain. Other objectives were to determine whether there were significant differences in the diagnosis and management of these patients depending on physician characteristics and/or patient profile. METHODS: This was an epidemiological, cross-sectional, multicentre study in which 107 physicians participated and recruited patients with Alzheimer's disease and CVD. During a 1-month period, physicians collected data on diagnosis, treatment, follow-up, adverse events and other characteristics of these patients. This study was performed under naturalistic conditions, and no restrictions were imposed on the physicians. RESULTS: Physicians were mainly neurologists (76%), geriatricians (14%) and psychiatrists (8%) with a median age of 42 years. A total of 720 patients with a diagnosis of Alzheimer's disease and CVD were recruited. The median age of the patients was 78 years. Almost all patients were diagnosed by neuroimaging (98%) together with medical history (87%). The existence of a previous stroke coincident with cognitive deterioration was used as a diagnostic method in only 27% of patients. Among non-pharmacological treatment measures, diet was the most frequently recommended (61%), followed by cognitive stimulation (50%) and physical exercise (44%). The most commonly used pharmacological treatments were galantamine (59%), donepezil (14%) and rivastigmine (11%). The incidence of adverse events was low (3%), and all were considered non-severe. There were no significant correlations between physician age or physician years of practice and the diagnostic method used. The diagnostic method most frequently used by psychiatrists (100%) and geriatricians (97%) was medical history whereas this method was not used as much by neurologists (85%) [p = 0.0150]. Neuroimaging methods were more frequently used by neurologists (99%) and geriatricians (96%) compared with psychiatrists (84%) [p < 0.0001]. Patients with attention disorders had a higher frequency of follow-up visits (p = 0.0145) and were treated less frequently with donepezil (p = 0.0118). CONCLUSIONS: Several possible areas of improvement in the management of patients with Alzheimer's disease and CVD were identified. These included better control of cardiovascular risk factors, such as hypertension and hyperlipidaemia, which have a high prevalence in this population, as has been shown in the present study. These potentially modifiable risk factors may assist in the prevention of Alzheimer's disease. Also identified was the need to emphasize the role of general practitioners in decreasing the time to diagnosis of Alzheimer's disease. Development of well designed clinical practice guidelines may help physicians decide on the most appropriate ways of diagnosing and managing patients with Alzheimer's disease and CVD and reduce practice variations between different medical specialities.

Comparison of hospital costs and length of stay associated with general internists and hospitalist physicians at a community hospital.

OBJECTIVE: To compare initial and long-term hospital resource utilization of hospitalists and general internists at an urban community hospital. STUDY DESIGN: A retrospective cohort analysis. METHODS: Data were collected from 11 750 admissions associated with 28 diagnosis-related groups for 6 years (October 1, 1994, to September 30, 2000). Hospital cost, length of stay, mortality, and 30-day readmission rates of general and hospitalist internists were analyzed for comparison. RESULTS: Hospitalists had generally lower utilization compared with general internists. Overall, length of stay and hospital cost were 16.1% and 8.3% lower, respectively, for hospitalists. Hospital mortality and 30-day readmissions were similar for both physician groups. CONCLUSIONS: Hospital resource utilization is moderately lower for hospitalists compared with private practicing general internists.