Yves M. Tourre

Characteristics of low-frequency sea surface temperature fluctuations in the tropical atlantic

Abstract Sea surface temperature anomalies in the tropical Atlantic Ocean are reexamined to investigate an apparent low-frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the ITCZ. Using principal components rotated by the varimax method and simple correlations of area-averaged temperatures, we show that during the 1964–88 interval SST anomalies north and south of the ITCZ are not significantly correlated. Therefore, the low-frequency variation, with an apparent decadal period observed in the SST gradient across the ITCZ during 1964–88, does not arise from temporally coherent and out-of-phase fluctuations in each hemisphere and cannot be characterized as a dipole.

ENSO Signals in Global Upper-Ocean Temperature

Abstract The time-space evolution of the El Nino-Southern Oscillation in sea surface temperature (SST) and heat storage of the upper 400 m (HS400) for the Pacific, Indian, and Atlantic Oceans is investigated for 13 years (1979–1991). EOF and rotated EOF (Varimax or VRX) analyses are performed using the time series of normalized anomalies for each ocean separately and then for the global ocean. In the Pacific and Indian Oceans, the two dominant EOF modes for both SST and H5400 are associated with ENSO. For SST they account for 49% of the total variance in each mean, while for H5400 they account for over 35% of the total variance in each ocean. In the Pacific Ocean, the first EOF modes for SST and HS400 display peak values during spring-summer of 1983 and 1987. They are characterized by maximum positive loadings (or warmer temperature) in the eastern and central Pacific Ocean straddling the equator. These modes represent the peak phase of El Nino off the west coast of South America. The second modes for SST...

Dominant Patterns of Climate Variability in the Atlantic Ocean during the Last 136 Years

Abstract Dominant spatiotemporal patterns of joint sea surface temperature (SST) and sea level pressure (SLP) variability in the Atlantic Ocean are identified using a multivariate frequency domain analysis. Five significant frequency bands are isolated ranging from the quasi biennial to the quasi decadal. Two quasi-biennial bands are centered around 2.2- and 2.7-yr periods; two interannual bands are centered around 3.5- and 4.4-yr periods; the fifth band at the quasi-decadal frequency is centered around 11.4-yr period. Between 1920 and 1955, the quasi-decadal band is less prominent compared to the quasi-biennial bands. This happens to be the period when SLP gradually increased over the Greenland–Iceland regions. The spatial pattern at the quasi-decadal frequency displays an out-of-phase relationship in the SLP in the vicinity of the subtropical anticyclones in both hemispheres (indicative of an out-of-phase quasi-decadal variability in the North and South Atlantic Hadley circulation). The quasi-decadal fr...

Patterns of coherent decadal and interdecadal climate signals in the Pacific Basin during the 20th century

Two distinct low-frequency fluctuations are suggested from a joint frequency domain analysis of the Pacific Ocean (30°S-60°N) sea surface temperature (SST) and sea level pressure (SLP). The lowest frequency signal reveals a spatially coherent interdecadal evolution, In-phase SST and SLP anomalies are found along the subarctic frontal zone (SAFZ). It is symmetric about the equator, with tropical SST anomalies peaking near 15° latitudes in the eastern Pacific. The other low-frequency signal reveals a spatially coherent decadal evolution. It is primarily a low-latitude phenomenon. Tropical SST anomalies peak in the central equatorial ocean with evidence of atmospheric teleconnections. These interdecadal and decadal signals join the ENSO and quasi-biennial signals in determining dominant patterns of Pacific Ocean natural climate variability. Relative phasing and location of the SST and SLP anomalies for the decadal, ENSO, and the quasi-biennial signals, are similar to one another but significantly different from that of the interdecadal signal.

Observed decadal midlatitude and tropical Atlantic climate variability

Two common indicators of Atlantic climate variability, viz., the North Atlantic oscillation (NAO) and the cross-intertropical convergence zone (ITCZ) sea surface temperature (SST) gradient, are examined for their frequency characteristics and, midlatitude-tropical links. SST anomalies north and south of the ITCZ are found to be uncorrelated on all time scales, while the sea level pressure (SLP) fluctuations associated with the NAO display a coherent seesaw between Iceland and the Azores. This out-of-phase relationship spans a broad range of time scales, but is particularly strong in the 5–10 year period band. Strong, broadband coherence between the NAO and the tropical Atlantic cross-ITCZ SST difference is found in the 8–20 year period band, suggesting a significant midlatitude-tropical interaction. Moreover, tropical Atlantic SSTs on both sides of the ITCZ, separately, exhibit significant coherence with the NAO index and SLP variability over Iceland and the Azores. Based on these findings we hypothesize that the tropical Atlantic (TA) ocean-atmosphere interaction is affecting North Atlantic climate variability.

Evolution of Interdecadal Variability in Sea Level Pressure, Sea Surface Temperature, and Upper Ocean Temperature over the Pacific Ocean*

Abstract Interdecadal variability in sea level pressure (SLP) and sea surface temperature (SST) anomalies in the Pacific Ocean was “quasiperiodic” from 1900–91. The coherent variability of this phenomenon is investigated using gridded observational data from the turn of the century (SST and SLP) and of upper ocean heat content (HS) from the recent two and a half decades. The nominal cycle in atmosphere–ocean variables is roughly two decades long, but growth and decay can happen on a shorter timescale (e.g., half a cycle or so). The authors divide the full cycle into four phases: An onset phase, during which a weak SLP anomaly pattern off Japan takes approximately 2–4 yr to expand eastward, leads to large SLP anomalies in the region of the Aleutian low. A quasi-stationary growth phase, with the midlatitude SLP anomaly pattern in the eastern ocean, intensifies over a 2–4-yr period. The persistent SLP anomalies evolve in concert with large SST (and HS anomalies) of the same polarity located to the south-sout...

Evolution of the ENSO Signal over the Indo–Pacific Domain*

Abstract The evolution of the El Nino–Southern Oscillation (ENSO) in the Indian and western Pacific Oceans is investigated. Observations of sea surface temperature (SST), heat storage in the upper 400 m (HS), zonal surface wind stress (ZSWS), and meridional surface wind stress (MSWS) are mapped monthly onto a 2° latitude–longitude grid over as much of the Indian and western Pacific Oceans (i.e., 40°S–50°N, 40°E–180°) as possible for a 13-year period (1979–91). This grid resolution allows upper-ocean temperature variability to be resolved in the eastern Indian Ocean (i.e., Timor Sea) and the western Pacific Ocean (i.e., Philippine Sea). Time sequences of these variables at each grid node are band-passed filtered to yield the ENSO period scales of 3 to 6 years. Extended empirical orthogonal functions analysis is applied to the filtered time sequences, yielding an animation of the ENSO development in Indian and western Pacific Oceans. For the first modes of the four variables (SST, HS, ZSWS, and MSWS) peak a...

Climate impacts on environmental risks evaluated from space: a conceptual approach to the case of Rift Valley Fever in Senegal

Background: Climate and environment vary across many spatio-temporal scales, including the concept of climate change, which impact on ecosystems, vector-borne diseases and public health worldwide. Objectives: To develop a conceptual approach by mapping climatic and environmental conditions from space and studying their linkages with Rift Valley Fever (RVF) epidemics in Senegal. Design: Ponds in which mosquitoes could thrive were identified from remote sensing using high-resolution SPOT-5 satellite images. Additional data on pond dynamics and rainfall events (obtained from the Tropical Rainfall Measuring Mission) were combined with hydrological in-situ data. Localisation of vulnerable hosts such as penned cattle (from QuickBird satellite) were also used. Results: Dynamic spatio-temporal distribution of Aedes vexans density (one of the main RVF vectors) is based on the total rainfall amount and ponds’ dynamics. While Zones Potentially Occupied by Mosquitoes are mapped, detailed risk areas, i.e. zones where hazards and vulnerability occur, are expressed in percentages of areas where cattle are potentially exposed to mosquitoes’ bites. Conclusions: This new conceptual approach, using precise remote-sensing techniques, simply relies upon rainfall distribution also evaluated from space. It is meant to contribute to the implementation of operational early warning systems for RVF based on both natural and anthropogenic climatic and environmental changes. In a climate change context, this approach could also be applied to other vector-borne diseases and places worldwide.

Mapping Entomological Dengue Risk Levels in Martinique Using High-Resolution Remote-Sensing Environmental Data

Controlling dengue virus transmission mainly involves integrated vector management. Risk maps at appropriate scales can provide valuable information for assessing entomological risk levels. Here, results from a spatio-temporal model of dwellings potentially harboring Aedes aegypti larvae from 2009 to 2011 in Tartane (Martinique, French Antilles) using high spatial resolution remote-sensing environmental data and field entomological and meteorological information are presented. This tele-epidemiology methodology allows monitoring the dynamics of diseases closely related to weather/climate and environment variability. A Geoeye-1 image was processed to extract landscape elements that could surrogate societal or biological information related to the life cycle of Aedes vectors. These elements were subsequently included into statistical models with random effect. Various environmental and meteorological conditions have indeed been identified as risk/protective factors for the presence of Aedes aegypti immature stages in dwellings at a given date. These conditions were used to produce dynamic high spatio-temporal resolution maps from the presence of most containers harboring larvae. The produced risk maps are examples of modeled entomological maps at the housing level with daily temporal resolution. This finding is an important contribution to the development of targeted operational control systems for dengue and other vector-borne diseases, such as chikungunya, which is also present in Martinique.

Impacts of Satellite-Based Rainfall Products on Predicting Spatial Patterns of Rift Valley Fever Vectors*

AbstractSpatiotemporal rainfall variability is a key parameter controlling the dynamics of mosquitoes/vector-borne diseases such as malaria, Rift Valley fever (RVF), or dengue. Impacts from rainfall heterogeneity at small scales (i.e., 1–10 km) on the risk of epidemics (i.e., host bite rate or number of bites per host and per night) must be thoroughly evaluated. A model with hydrological and entomological components for risk prediction of the RVF zoonosis is proposed. The model predicts the production of two mosquito species within a 45 km × 45 km area in the Ferlo region, Senegal. The three necessary steps include 1) best rainfall estimation on a small scale, 2) adequate forcing of a simple hydrological model leading to pond dynamics (ponds are the primary larvae breeding grounds), and 3) best estimate of mosquito life cycles obtained from the coupled entomological model. The sensitivity of the model to the spatiotemporal heterogeneity of rainfall is first tested using high-resolution rain fields from a ...