M Nunez

Monthly Ambient Sunlight, Infections and Relapse Rates in Multiple Sclerosis

Background: Monthly variation in multiple sclerosis (MS) relapses has been found. The relationship between seasonal environmental factors, infections, serum vitamin D [25(OH)D] and MS relapses is undetermined. Methods: We prospectively followed a population-based cohort of relapsing-remitting (RR) MS patients in Southern Tasmania for a mean 2.3 years (January 2002–April 2005). Associations between monthly ambient environmental factors, estimated serum 25(OH)D, upper respiratory tract (URT) infections and relapse rates were examined using weighted Pearson’s correlation and linear regression. Results: Of 199 definite MS patients, 142 had RRMS. The lowest relapse rate of 0.5 per 1,000 days (95% CI: 0.2–1.3) occurred in February (mid-late summer) versus the March–January RR of 1.1 per 1,000 days (95% CI: 0.9–1.3; p = 0.018, weighted regression). Monthly relapse rates correlated with: (1) prior erythemal ultraviolet radiation (EUV): lagged 1.5 months, r = –0.32, p = 0.046; (2) URT infection rate: no lag, r = 0.39, p = 0.014; (3) 25(OH)D: no lag, r = –0.31, p = 0.057. The association between URT infections and relapses was reduced after adjustment for monthly EUV. Conclusions: Relapse rates were inversely associated with EUV and serum 25(OH)D levels and positively associated with URT infections. The demonstrated lag between EUV but not 25(OH)D and relapse rates is consistent with a role for EUV-generated 25(OH)D in the alteration of relapse rates. Future work on the association between URT infections and relapses should be considered in the context of ultraviolet radiation and vitamin D.

Narrow-band to broad-band conversion for Meteosat-visiible channel and broad-band albedo using both AVHRR-1 and -2 channels

Abstract Satellite-derived broad-band albedo offers a useful tool for monitoring surface conditions. Given the limited wavelength window of most satellite radiometers, satellite albedo studies need to define narrow-band to a broad-band transformations. Signals from the AVHRR channels on board the NOAA-11 satellite, the Meteosat visible channel and a rectangular spectral band from 0-3 to 2.5 μm were simulated for a set of 20 representative land surfaces. The radiative transfer code described in Tanre et al. (1990) was used to obtain top of the atmosphere radiances. The derived signals were then correlated to predict broadband albedo and the Meteosal response via the two AVHRR signals. The results indicated that the use of the two AVHRR bands makes the narrow-band to broad-band conversion independent of the surface type. Finally, the regression was applied to two concurrent AVHRR and Meteosat images so as to compare a broad-band AVHRR-derived top of the atmosphere (TOA) albedo for the Meteosat-band with a c...

A METHOD FOR FINDING SEA BREEZE DAYS UNDER STABLE SYNOPTIC CONDITIONS AND ITS APPLICATION TO THE SWEDISH WEST COAST

A method for selecting sea breeze days in an archipelago was developed with special application to the West Coast of Sweden. The primary criterion for identifying a sea breeze was the occurrence of a distinct change in surface wind direction within a 24 h period. The data used in the study were gathered using hourly meteorological records from field stations situated on the West Coast. Six different filters were included in the method; each of them developed from empirical knowledge of the physical processes responsible for the occurrence of a sea breeze system. Using this method it is possible to create a data set of sea breeze days, which does not use distance to the shoreline as a necessary condition for classification.

Vegetation-radiation relationships in mountainous terrain: eucalypt-dominated vegetation in the Risdon Hills, Tasmania

The vegetation along a north-south transect across a valley in the Risdon Hills, Tasmania, varies from Eucalyptus globulus-E, viminalis-E. amyg- dalina open-forest with a dense understorey of broad-leaved shrubs toE. Risdonii open-scrub with a sparse understorey of sclerophyll shrubs and graminoids. The variation in vegetation along the transect is highly correlated with total annual solar radiation, calculated to include the effects of shading, cloud cover and the sky view factor. The distributions of a large proportion of the species found along the transect are most highly significantly correlated with the solar radi- ation received in one of the solstice months. However, the response of most species to variation in incident solar radiation is curvilinear rather than linear. The topographically driest site does not possess the most xeric vegetation. This deflection is probably a consequence of downslope movement of soil moisture and runoff. Also, the most xeric vegetation tends to occur on northwest rather than north-facing slopes, possibly a result of an evapotranspiration peak in late

Measurements of erythemal irradiance near Davis Station, Antarctica: Effect of inhomogeneous surface albedo

To examine effects of inhomogeneous surface albedo on UV irradiance, measurements were taken near Davis Station (68.58°S, 77.97°E), East Antarctica during November/December 1997. Data were collected in transects perpendicular to an ice/water boundary, while one instrument continuously measured at the ice edge. Irradiances along transects were normalised by coincident measurements at the ice edge. Systematic differences in downwelling irradiance near the ice edge were observed over the highly reflective surface and open water. For cloudless conditions, the relative change in irradiance reached limiting values of about +5% from the ice edge to a point 2.5 km over snow-covered ice, and about −5% from the ice edge to a point 2.5 km over water. In overcast conditions, higher relative changes were observed (about +30% from the ice edge to a point 2.5 km over ice on 17 November 1997) with no sign of a constant relative change being reached.

Estimating ultraviolet radiation at the earth's surface

Surface ultraviolet (UV) irradiance depends not only on stratospheric ozone amounts, but also varies with time and date, latitude, cloud amount and aerosol load. Any assessment of the effect of stratospheric ozone depletion on surface UV irradiance must take into consideration all of the above parameters. Measurements in the UV-B region may be accomplished using filter and detector combinations which mimic a biological response curve. However there are uncertainties such as in determining the exact filter response and in the cosine error of the detector. The UV-A region lacks a strong ozone absorption band and approaches which relate measured UV-A irradiance to measured global irradiance show promise. Theoretical models have been derived which calculate spectral UV irradiance in cloudless and cloudy conditions. Results show that cloud transmissivities increase as wavelength increases; however, there is a strong dependence on cloud type. In the absence of surface observations of clouds, satellite data may be used to map UV-A and UV-B irradiance in a region, and this approach is illustrated using two specific examples.

A 10-year climatology of solar radiation for the Great Barrier Reef: implications for recent mass coral bleaching events

A 10‐year solar radiation climatology is developed for the Great Barrier Reef region using data from the Geostationary Meteorological Satellite (GMS). The method uses a look‐up table based on the STREAMER radiative transfer model for a tropical atmosphere. One outstanding feature appears in the summer and autumn climatologies which exhibit distinct maxima in the southern end of the study area, between latitudes 18° S and 26° S. There is a small but statistically significant increase in solar radiation over the 10‐year study period, with maximum values of just under 1% per decade. The radiation climatology was used to examine previous coral bleaching episodes, and in particular the largest mass bleaching episode that occurred in 2002. Results show that the area of maximum bleaching corresponded closely to the area of maximum solar insolation. Sea surface temperature and solar radiation were used in a variance analysis to discriminate bleached from unbleached reefs. Solar radiation is a better discriminator for inshore areas, but temperature is better at discriminating offshore reefs. Possible reasons for this difference are discussed.

Conversion of nadir, narrowband reflectance in red and near-infrared channels to hemispherical surface albedo

Abstract Measured nadir-viewed narrow-band reflectanees in red and near infrared channels simulating AVHRR Channels 1 and 2 are compared with measured integrated solar spectrum hemispherical albedos. Reflectanees and albedos were measured from an aircraft over four widely different vegetation surfaces in southeastern Tasmania (Australia). A linear function is used to simultaneously correct for narrow band to broad band conversion errors and to convert nadir viewed reflectances to hemispherical albedos. While the application of the conversion equation presented is limited to the vegetation types of the study, the equation is independent of vegetation type. Results indicate that the reflectance from the rough surface of a forest canopy is not Lambertian and that the use of a directional to hemispherical albedo conversion using a Lambertian assumption may lead to errors as great as 35%.

Vegetation-radiation relationships in the wet-dry tropics: granite hills in northern Australia

A model of direct and diffuse solar radiation on slopes of varying angle and aspect suggests that radiation differences within hilly terrain are maximized in the beginning of the dry season in the monsoon tropics. The differences between north and south facing slopes are greater than those found during the summer in the temperate zone. Within a study area near Mt. Bundey, Northern Territory, floristic and structural vegetational variability is closely related to June radiation as estimated by the model. However, the distribution patterns of monsoon thicket and eucalypt forest relate more to relative five protection than to the effects of incident radiation on temporal patterns of moisture availability. Within both major formations, site rockiness is an important influence on vegetation floristics and structure, both for five protection and through its influence on moisture availability.

Ultraviolet Radiation Protection by a Beach Umbrella

A beach umbrella intercepts all direct UV irradiance, but only part of the diffuse component. Using a simple sky view factor model, we have determined the fraction of the hemispheric diffuse irradiance that is not intercepted by the umbrella. Assuming a sensor at the surface and close to the center of the umbrella, isotropic diffuse irradiance and for an umbrella of 80 cm radius and 100 cm high, our results show that approximately 34% of the incident horizontal irradiance is not intercepted by the umbrella. These results agree with irradiance measurements conducted with and without the umbrella. The model is next extended to examine receipt of UV radiation by a human figure in a vertical position, either standing or sitting.