Search results for "tropics"

High-frequency oscillations of the last 70,000 years in the tropical/subtropical and polar climates

1999

Fish introductions and light modulate food web fluxes in tropical streams : a whole-ecosystem experimental approach

2016

Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen (15N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. con…

Global equatorial variability of 850 and 200 hPa zonal winds from rawinsondes between 1963 and 1989

1995

The longitude-height-time variability of 3-month averaged zonal wind anomalies at 850 and 200 hPa over the equatorial area (5{degrees}N-5{degrees}S) is analyzed using a three-dimensional dataset constructed from rawinsonde data (1963-1989). The first mode, closely related to the Southern Oscillation Index, suggests a strong vertical coupling associated with a horizontal out-of-phase pattern between the central/western Pacific and the remainder of the equatorial belt. The vertical coupling appears to be phase-locked to the annual cycle with strongest intensities found over South America and near the maritime continent early in the calendar year and over the Pacific basin and Africa during th…

Sea-surface temperature co-variability in the Southern Atlantic and Indian Oceans and its connections with the atmospheric circulation in the Souther…

2003

The relationship between sea-surface temperature (SST) inter-annual variability at the subtropical and midlatitudes of the southern Atlantic and Indian Oceans and its links with the atmospheric circulation in the Southern Hemisphere are investigated over the 1950–1999 period. Exploratory analysis using singular value decomposition and further investigations based on simple indices show that a large part of regional SST variability is common between the southwestern parts of both basins at subtropical and midlatitudes during the austral summer. Interestingly, these areas are also significantly associated with the far southwestern Pacific (Tasman Sea area). The patterns and time series of co-…

Changes in the African monsoon region at medium-term time horizon using 12 AR4 coupled models under the A1b emissions scenario.

2011

This study documents simulated precipitation and circulation changes through the 20C3M and A1b scenarios. It portrays a robust pattern, associating rainfall deficits in subtropical regions with rainfall excesses over West Africa, except in Northern Senegal and Mauritania, with a significant enhancement of both the April–June rainy season in 10/12 models and of the July–September rainy season in 8/12 models. Eastward to 5°W a northward shift in the latitude of the moisture flux convergence at 850 hPa is evident in 10/11 models (+0.58° in mean) and a southward shift in 6/11 models in the western region (−0.24°) is observed. Copyright © 2011 Royal Meteorological Society

June-september rainfall in north-eastern Africa and atmospheric signals over the tropics: A zonal perspective

1995

The connection between rainfall in northeast Africa (Djibouti, Eritrea, Ethiopia, Kenya, Somalia, Sudan, and Uganda) and various atmospheric indicators from the tropics have been investigated for the northern summer season. Variables used include zonal wind at 700 hPa and 200 hPa, sea-level pressure, and rainfall over other tropical areas, for the period 1951–1988. Strong significant correlations are shown with the Southern Oscillation and the components of the Walker cell in the Pacific Ocean. Droughts in the Ethiopia-Uganda area are associated with El Nino events and, moreover, with above normal pressure and droughts over India. Other significant relationships exist with the African monso…

The Stationarity of Lead-Lag Teleconnections with East Africa Rainfall and its Incidence on Seasonal Predictability

2001

East Africa experiences large interannual rainfall variations, which can lead to severe droughts, as in 1984 in Ethiopia, or extensive flooding, as in 1997 in Somalia and Kenya. In the last 15 years, significant advances have been made in relating these variations to large-scale ocean-atmosphere anomalies, of which those associated to ENSO (El Nino Southern Oscillation) come first. The additional importance of sea-surface variations in the Tropical Atlantic and Indian Oceans is becoming established. Although 20th century East African precipitation series did not experience decadal-scale trends as significant as those found in the sahelian belt, the correlation with ENSO, the Indian monsoon …

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…

Castniidae of the Museum of Natural History of the University of Wrocław: new findings from Friedrich Wilhelm Niepelt's collection with comments on K…

2021

Further results of our research into the Giant Butterfly-Moths (Castniidae) of the Museum of Natural History (University of Wrocław) are presented. Castniids of the Niepelt collection had previously been reviewed. However, while curating other sections of the Lepidoptera collection, we discovered 18 misplaced specimens belonging to nine taxa of Castniidae, several of them bearing typical labels by Niepelt. Among them, two are of particular interest, insofar as they are associated with the world-class botanists August Weberbauer (1871–1948) and Karl Adolf Georg Lauterbach (1864–1937).

Retention forestry and biodiversity conservation: a parallel with agroforestry

2013

In forested landscapes two general management systems – retention forestry and agroforestry – have been proposed as potentially efficient components of landscape approaches to ease the conflict between biodiversity objectives and human needs. In two recent reviews, Gustafsson et al. (2012) and Lindenmayer et al. (2012) provide a global overview of current knowledge about the practice and ecological roles of retention forestry. A few years ago, Bhagwat et al. (2008) produced a similar review addressing the role of agroforestry in biodiversity conservation. Here we draw a parallel between research on the ecological effects of retention forestry and agroforestry. We argue that conservation sci…