Search results for "Convergence zone"
showing 7 items of 27 documents
Inter-Relationships Between Groundnut Yield in Senegal, Interannual Rainfall Variability and Sea-Surface Temperatures
1999
Groundnut production strongly contributes to Senegal’s economy. Interannual variations of groundnut yield for the country as a whole, and their relationship with rainfall amounts, are examined for the 31-yr period 1960–1990. It is shown that on that scale, and after removing decadal trends, almost half of the variance is explained by rainfall variability, especially that of the early part of the rainy season (July–August). Given the high spatial coherence of seasonal rainfall in the region, teleconnections with global- and regional-scale climate dynamics, including sea-surface temperatures, are assessed. Though some features are similar to the rest of the Sahel, others are more specific, su…
The East African March–May Rainy Season: Associated Atmospheric Dynamics and Predictability over the 1968–97 Period
2002
Abstract This paper focuses on the East African March–May “long rains.” Particularly, it investigates the atmospheric patterns associated to the March–May rainfall anomalies, then proposes a seasonal prediction model. In a preliminary step, in order to define a regional rainfall index, a new form of extended principal component analysis is performed, aimed at capturing both the spatial and intraseasonal rainfall coherence. What emerges is that although the long rains exhibit a low temporal coherence, calling for a separation between the months of March–April and May in teleconnection studies, they show a relatively strong spatial consistency over the Kenya–Uganda inland region. From composi…
Intraseasonal wind anomalies related to wet and dry spells during the ?long? and ?short? rainy seasons in Kenya
1997
The largest part of Kenya exhibits two major rainy seasons, the March–May «long rains» and the October–December «short rains», both related to the passage of the ITCZ, but differing in the amount of rainfall recorded and its interannual variability. In order to investigate whether these differences also apply at intraseasonal time-scales, daily rainfall data for the peak month of each rainy season (April and November) were collected for 7 consecutive years (1982–1988). The network comprises 68 stations, from which a classification of the spatial patterns of daily rainfall anomalies has been performed. Wind anomalies corresponding to the various rainfall types and to specific regional rainfa…
The Aqua-Planet Experiment (APE): Response to Changed Meridional SST Profile
2013
This paper explores the sensitivity of Atmospheric General Circulation Model (AGCM) simulations to changes in the meridional distribution of sea surface temperature (SST). The simulations are for an aqua-planet, a water covered Earth with no land, orography or sea- ice and with specified zonally symmetric SST. Simulations from 14 AGCMs developed for Numerical Weather Prediction and climate applications are compared. Four experiments are performed to study the sensitivity to the meridional SST profile. These profiles range from one in which the SST gradient continues to the equator to one which is flat approaching the equator, all with the same maximum SST at the equator. The zonal mean circ…
Late Quaternary Variations in the South American Monsoon System as Inferred by Speleothems – New Perspectives Using the SISAL Database
2018
Here we present an overview of speleothem δ18O records from South America, most of which are available in the Speleothem Isotopes Synthesis and Analysis (SISAL_v1) database. South American tropical and subtropical speleothem δ18O time series are primarily interpreted to reflect changes in precipitation amount, the amount effect, and consequently history of convection intensity variability of convergence zones such as the Intertropical Convergence Zone (ITCZ) and the South America Monsoon System (SAMS). We investigate past hydroclimate scenarios in South America related to the South American Monsoon System in three different time periods: Late Pleistocene, Holocene, and the last two millenni…
Millennial-scale climate variability during the last 12.5 ka recorded in a Caribbean speleothem
2013
Abstract We present a speleothem stable oxygen isotope record for the last 12.5 ka based on two stalagmites from western Cuba. The δ18O signal is interpreted to represent past precipitation variability. Both stalagmites show a pronounced transition from higher δ18O values (indicating drier conditions) to more negative δ18O values (suggesting wetter conditions) between 10 and 6 ka. This transition is also visible in a planktonic δ18O record off Haiti. On orbital timescales, the δ18O value of Caribbean precipitation, thus, strongly resembles the oxygen isotope composition of Caribbean surface water. On millenial timescales, the speleothem δ18O record shows a high correlation to a North Atlant…
The Aqua-Planet Experiment (APE): CONTROL SST Simulation
2013
Climate simulations by 16 atmospheric general circulation models (AGCMs) are compared on an aqua-planet, a water-covered Earth with prescribed sea surface temperature varying only in latitude. The idealised configuration is designed to expose differences in the circulation simulated by different models. Basic features of the aqua-planet climate are characterised by comparison with Earth. The models display a wide range of behaviour. The balanced component of the tropospheric mean flow, and mid-latitude eddy covariances subject to budget constraints, vary relatively little among the models. In contrast, differences in damping in the dynamical core strongly influence transient eddy amplitudes…