19 research outputs found
Climate impacts on environmental risks evaluated from space: a conceptual approach to the case of Rift Valley Fever in Senegal
The 1983 drought in the West Sahel: a case study
Some drought years over sub-Saharan west Africa (1972, 1977, 1984) have been previously related to a cross-equatorial Atlantic gradient pattern with anomalously warm sea surface temperatures (SSTs) south of 10°N and anomalously cold SSTs north of 10°N. This SST dipole-like pattern was not characteristic of 1983, the third driest summer of the twentieth century in the Sahel. This study presents evidence that the dry conditions that persisted over the west Sahel in 1983 were mainly forced by high Indian Ocean SSTs that were probably remanent from the strong 1982/1983 El Niño event. The synchronous Pacific impact of the 1982/1983 El Niño event on west African rainfall was however, quite weak. Prior studies have mainly suggested that the Indian Ocean SSTs impact the decadal-scale rainfall variability over the west Sahel. This study demonstrates that the Indian Ocean also significantly affects inter-annual rainfall variability over the west Sahel and that it was the main forcing for the drought over the west Sahel in 1983
Patterns of Pacific decadal variability recorded by Indian Ocean corals
We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral δ18O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies, we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La Réunion (Ifaty) coral better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La Réunion coral δ18O represents δ18O of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty coral δ18O represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La Réunion boreal summer δ18O series explains about 64% of the variance of the coupled SST/SLP PDO time series
A recipe for simulating the interannual variability of the Asian summer monsoon and its relation with ENSO
Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Climate Dynamics 28 (2007): 441-460, doi: 10.1007/s00382-006-0190-0.This study investigates how accurately the interannual variability over the Indian
Ocean basin and the relationship between the Indian summer monsoon and the
El Nino Southern Oscillation (ENSO) can be simulated by different modelling
strategies. With a hierarchy of models, from an atmospherical general circulation
model (AGCM) forced by observed SST, to a coupled model with the ocean
component limited to the tropical Pacific and Indian Oceans, the role of heat
fluxes and of interactive coupling is analyzed. Whenever sea surface temperature
anomalies in the Indian basin are created by the coupled model, the inverse relationship
between the ENSO index and the Indian summer monsoon rainfall is
recovered, and it is preserved if the atmospherical model is forced by the SSTs
created by the coupled model. If the ocean model domain is limited to the Indian
Ocean, changes in the Walker circulation over the Pacific during El Nino years
induce a decrease of rainfall over the Indian subcontinent. However the observed
correlation between the ENSO and the Indian Ocean Zonal Mode (IOZM) is
not properly modelled and the two indices are not significantly correlated, independently
on season. Whenever the ocean domain extends to the Pacific, and
ENSO can impact both the atmospheric circulation and the ocean subsurface in
the equatorial Eastern Indian Ocean, modelled precipitation patterns associated
both to ENSO and to the IOZM closely resemble the observations.The experiments described were performed as a contribution to the ENSEMBLES
project funded by the European Commission’s 6th Framework Programme, contract
number GOCE-CT-2003-505539
Ecological commonalities among pelagic fishes: comparison of freshwater ciscoes and marine herring and sprat
Systematic comparisons of the ecology between functionally similar fish species from freshwater and marine aquatic systems are surprisingly rare. Here, we discuss commonalities and differences in evolutionary history, population genetics, reproduction and life history, ecological interactions, behavioural ecology and physiological ecology of temperate and Arctic freshwater coregonids (vendace and ciscoes, Coregonus spp.) and marine clupeids (herring, Clupea harengus, and sprat, Sprattus sprattus). We further elucidate potential effects of climate warming on these groups of fish based on the ecological features of coregonids and clupeids documented in the previous parts of the review. These freshwater and marine fishes share a surprisingly high number of similarities. Both groups are relatively short-lived, pelagic planktivorous fishes. The genetic differentiation of local populations is weak and seems to be in part correlated to an astonishing variability of spawning times. The discrete thermal window of each species influences habitat use, diel vertical migrations and supposedly also life history variations. Complex life cycles and preference for cool or cold water make all species vulnerable to the effects of global warming. It is suggested that future research on the functional interdependence between spawning time, life history characteristics, thermal windows and genetic differentiation may profit from a systematic comparison of the patterns found in either coregonids or clupeids