Search results for "surface temperature"
showing 10 items of 218 documents
Autonomous Measurements of Sea Surface Temperature Using In Situ Thermal Infrared Data
2004
Abstract In situ and autonomous measurements of sea surface temperature (SST) have been performed with a thermal infrared radiometer mounted on a fixed oil rig. The accuracy limit was established at ±0.3 K for these SST measurements in order to meet the requirements of the Tropical Ocean Global Atmosphere (TOGA) program for global climate research and the Soil Moisture and Ocean Salinity (SMOS) mission for salinity retrieval. With this aim, the optimal observation angle and spectral channel for SST measurements have been identified. Then, a methodology has been developed for the radiometer calibration and the emissivity correction, including the reflection of the downwelling sky radiance, w…
Summer Sahel-ENSO teleconnection and decadal time scale SST variations
2001
The correlation between Sahel rainfall and El Nino–Southern Oscillation (ENSO) in the northern summer has been varying for the last fifty years. We propose that the existence of periods of weak or strong relationship could result from an interaction with the global decadal scale sea surface temperature (SST) background. The main modes of SST variability have been extracted through a principal component analysis with Varimax rotation. The correlations between a July-September Sahel rainfall index and these SST modes have been computed on a 20-year running window between 1945 and 1993. The correlations with the interannual ENSO-SST mode are negative, not significant in the 1960s during the tr…
Exploring the predictability of the‘Short Rains’ at the coast of East Africa
2004
The boreal autumn ‘Short Rains’ at the coast of East Africa are deficient when there is weak development of a zonal circulation cell along the Indian Ocean equator, an anomalously low sea-surface temperature in the western portion of the basin, and in the high phase of the southern oscillation. Such large-scale circulation departures and their precursors are described by compact indices. September values of these indices for the period 1958–96 are used to explore the predictability of an index (RON) of October–November rainfall at the coast of East Africa. Regressions with cross-validation over the entire 1958–96 period are evaluated for the early (1958–77) and late (1978–96) halves of the …
20th century droughts in southern Africa: spatial and temporal variability, teleconnections with oceanic and atmospheric conditions
2001
Southern African rainfall does not show any trend to desiccation during the 20th century. However, the subcontinent experienced particularly severe droughts in the 1980s and at the beginning of the 1990s and the magnitude of the interannual summer rainfall variability shows significant changes. Modifications of the intensity and spatial extension of droughts is associated with changes in ocean–atmosphere teleconnection patterns. This paper focuses mostly on the well-documented 1950–1988 period and on late summer season (January–March). A principal component analysis on southern African rainfall highlights modifications of the rainfall variability magnitude. The 1970–1988 period had more var…
Sea Surface Temperature Fields Associated with West African Rainfall Anomaly Types
1996
Abstract Four West African rainfall anomaly types are defined in relation to the northern summer rainfall departure signs in the Sahel and in the Guinean region in order to investigate the statistical links between interannual variability of West African rainfall and sea surface temperature (SST) through the period 1950–90. Composite analysis depicts the setup of four different mean SST anomaly fields. Drought over all of West Africa is associated with the growth of positive SST anomalies in the eastern Pacific and in the Indian Ocean, and negative SST anomalies in the northern Atlantic and in the Gulf of Guinea. In contrast, drought limited to the Sahel corresponds mostly to a northward ex…
Seasonality and atmospheric dynamics of the teleconnection between African rainfall and tropical sea-surface temperature: Atlantic vs. ENSO
2001
A 47-year record (1951-1997) of gridded data covering Africa south of the Sahara was used to document the spatial and seasonal patterns of the correlation between precipitation and sea-surface temperatures (SST) in key tropical areas, as depicted by the NIN O3, South Atlantic and North Atlantic indices. El Nino -Southern Oscillation (ENSO) is confirmed as playing a dominant part in northeastern, eastern and southern Africa. However, its impact is also found over the Sahel during the northern summer, and other parts of the Gulf of Guinea region outside this season, a hitherto poorly documented feature. Over these two areas, ENSO and Atlantic SST (predominantly South Atlantic) contribute to d…
Modification of the southern African rainfall variability/ENSO relationship since the late 1960s
2000
Analysis of 149 raingauge series (1946–1988) shows a weak positive correlation between late summer rainfalls (January–March) in tropical southern Africa and the Southern Oscillation Index (SOI). The correlation coefficients have been unstable since World War II. They were close to zero before 1970 and significant thereafter. Before 1970, southern African late summer rainfalls were more specifically correlated with regional patterns of sea surface temperature (SST), mainly over the southwestern Indian Ocean. After 1970, teleconnections with near global SST anomaly patterns, i.e. over the central Pacific and Indian oceans, dominate the regional connections. The increase in the sensitivity of …
Predicting dengue fever outbreaks in French Guiana using climate indicators
2016
Background Dengue fever epidemic dynamics are driven by complex interactions between hosts, vectors and viruses. Associations between climate and dengue have been studied around the world, but the results have shown that the impact of the climate can vary widely from one study site to another. In French Guiana, climate-based models are not available to assist in developing an early warning system. This study aims to evaluate the potential of using oceanic and atmospheric conditions to help predict dengue fever outbreaks in French Guiana. Methodology/Principal Findings Lagged correlations and composite analyses were performed to identify the climatic conditions that characterized a typical e…
Foam effect on the sea surface emissivity in the 8–14μm region
2007
[1] The effect of foam on the sea surface emission has been studied in the microwave region, but its effect on thermal infrared emissivity and temperature has not been sufficiently analyzed in the literature. This paper presents thermal infrared measurements of foam-covered seawaters carried out under controlled conditions using a multichannel radiometer working in the 8–14 μm region. The experimental data show a negligible foam effect at low observation angles but a significant increase of emissivity with foam at angles above 45°. Differences between foam and foam-free emissivities are about +0.04 for observation angles of 65°, depending slightly on the radiometric spectral band. The effec…
Temperature changes in the mid- and high- latitudes of the Southern Hemisphere
2012
A Hierarchical Ascending Classification is used to regionalize monthly temperature anomalies measured at 24 weather stations in Antarctica and the Sub-Antarctic and mid-latitude southern islands from 1973 to 2002. Three principal regions are identified that are geographically coherent: Eastern Antarctica, the Antarctic Peninsula and the Sub-Antarctic and mid-latitude islands. Within each region, consistent trends are observed: namely, stationary temperatures in ‘East-Antarctica’; a robust warming in the ‘Sub-Antarctic and mid-latitude islands’, most pronounced in austral summer (nearly 0.5 °C per decade); and a strong but more recent warming in the ‘Antarctic Peninsula’. Austral summer temp…