Trends of upper-air circulation and water vapour over equatorial South America and adjacent oceans

Curtis, Scott; Hastenrath, Stefan

doi:10.1002/(sici)1097-0088(19990630)19:8<863::aid-joc394>3.0.co;2-2

Cited by 33 publications

(12 citation statements)

References 25 publications

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“…Chen et al (2001) find a rainfall increase in the AB countries since the 1960s using data from Global Historical Climatology Network (GHCN). This is in line with the increase in humidity convergence, described by Chu et al (1994) and Curtis and Hastenrath (1999). Nevertheless, this trend is not valid for Callède et al (2004), who rebuilt a pluviometric series for the period 1945-1998 based on 43 pluviometric posts, and observe an slightly decreasing trend for the period, with the exception of high values recorded from 1965to 1975.…”

Section: Introductionmentioning

confidence: 75%

Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

Espinoza

Ronchail

Guyot

et al. 2008

Intl Journal of Climatology

458

265

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Rainfall variability in the Amazon basin (AB) is analysed for the 1964-2003 period. It is based on 756 pluviometric stations distributed throughout the AB countries. For the first time it includes data from Bolivia, Peru, Ecuador, and Colombia. In particular, the recent availability of rainfall data from the Andean countries makes it possible to complete previous studies. The impact of mountain ranges on rainfall is pointed out. The highest rainfall in the AB is observed in low windward regions, and low rainfall is measured in leeward and elevated stations. Additionally, rainfall regimes are more diversified in the Andean regions than in the lowlands. Rainfall spatio-temporal variability is studied based on a varimax-rotated principal component analysis (PCA). Long-term variability with a decreasing rainfall since the 1980s prevails in June-July-August (JJA) and September-October-November (SON). During the rainiest seasons, i.e. December-January-February (DJF) and March-April-May (MAM), the main variability is at decadal and interannual time scales. Interdecadal variability is related to long-term changes in the Pacific Ocean, whereas decadal variability, opposing the northwest and the south of the AB, is associated with changes in the strength of the low-level jet (LLJ) along the Andes. Interannual variability characterizes more specifically the northeast of the basin and the southern tropical Andes. It is related to El Niño-Southern Oscillation (ENSO) and to the sea surface temperature (SST) gradient over the tropical Atlantic. Mean rainfall in the basin decreases during the 1975-2003 period at an annual rate estimated to be −0.32%. Break tests show that this decrease has been particularly important since 1982. Further insights into this phenomenon will permit to identify the impact of climate on the hydrology of the AB.

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Section: Introductionmentioning

confidence: 75%

Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

Espinoza

Ronchail

Guyot

et al. 2008

Intl Journal of Climatology

458

265

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“…The anomalously strong northeasterly trades should also bring about increased moisture convergence in the Amazon Basin and increased precipitation in the southern tropics of South America, including much of the Amazon and tropical Andes. In fact, Curtis and Hastenrath (1999), examining reanalysis data from 1958 to 1997, documented an example of such a long-term increase of the Atlantic northeasterly trades that supported a long-term increase in moisture convergence in the Amazon region. The trend observed by Curtis and Hastenrath (1999) also coincided with a nearly 40 year period of increasing winter NAO index (Hurrell and Van Loon 1997).…”

Section: Discussionmentioning

confidence: 99%

The Nature and Origin of Decadal to Millennial Scale Climate Variability in the Southern Tropics of South America: The Holocene Record of Lago Umayo, Peru

Baker

Fritz

Burns

et al. 2009

Developments in Paleoenvironmental Research

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This paper serves two purposes: to review current ideas about the nature and forcing of decadal to millennial scale precipitation variation in the southern tropics of South America during the late Quaternary and to present a new methodology for the reconstruction of precipitation as applied to a Holocene stable isotopic record of carbonate sediments in a tropical Andean lake, Lago Umayo, Peru. The basic thesis of the first part of the paper is that, although modern instrumental records suffice for deducing climate variability at decadal and shorter time scales, these records cannot adequately characterize the nature and forcing of lower-frequency climate variation. Understanding the nature of multi-decadal to millennial-scale climate variation and the mechanisms of large abrupt climate change is best derived from paleoclimatic time series. Tropical Atlantic sea-surface temperature variation is a significant control on tropical South American paleoclimate at these longer time scales. In the second part of the paper, an original method is presented for quantitatively reconstructing precipitation. This method utilizes the well-known relationship between the stable isotopic composition of precipitation and the amount of precipitation, a relationship that is highly significant in many tropical locales. Due to many simplifying assumptions, the reconstruction should be considered to be tentative.A ~12% increase in precipitation (~570 to 650 mm a -1 ) at 4750 cal year BP is consistent with the 6% increase in summer insolation at this latitude over the same period. However, the increase in precipitation was neither unidirectional nor gradual. Instead, every 240 years on average, precipitation increased or decreased by at least ~8% for periods lasting on average 100 years. The largest of these events had ~15% positive or negative departures from the long-term mean precipitation. These southern tropical wet events apparently coincided with periods of low sea-surface temperatures in the high-latitude North Atlantic, supporting a hypothesis of a tropical North Atlantic b a k e r e t a l . i n p a s t c l i m a t e v a r i a b i l i t y i n s o u t h a m e r i c a (2009) 302sea-surface temperature control on tropical South American precipitation at decadal to millennial scales.

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“…One possible mechanism is related to a change in the water balance of the basin, such as changes in the net amount of water vapor transported into the basin. The observed increases in river run-off and satellite observations on water-vapor transport (51) indicate that water import into the basin may have increased. If such increases in influx of water vapor exceed the increase in rainout and loss via river run-off, the isotope ratios would increase.…”

Section: -2001mentioning

confidence: 93%

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Niño-Southern Oscillation variability

Brienen

Helle

Pons

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

177

145

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We present a unique proxy for the reconstruction of variation in precipitation over the Amazon: oxygen isotope ratios in annual rings in tropical cedar (Cedrela odorata). A century-long record from northern Bolivia shows that tree rings preserve the signal of oxygen isotopes in precipitation during the wet season, with weaker influences of temperature and vapor pressure. Tree ring δ 18 O correlates strongly with δ 18 O in precipitation from distant stations in the center and west of the basin, and with Andean ice core δ 18 O showing that the signal is coherent over large areas. The signal correlates most strongly with basin-wide precipitation and Amazon river discharge. We attribute the strength of this (negative) correlation mainly to the cumulative rainout processes of oxygen isotopes (Rayleigh distillation) in air parcels during westward transport across the basin. We further find a clear signature of the El Niño-Southern Oscillation (ENSO) in the record, with strong ENSO influences over recent decades, but weaker influence from 1925 to 1975 indicating decadal scale variation in the controls on the hydrological cycle. The record exhibits a significant increase in δ 18 O over the 20th century consistent with increases in Andean δ 18 O ice core and lake records, which we tentatively attribute to increased water vapor transport into the basin. Taking these data together, our record reveals a fresh path to diagnose and improve our understanding of variation and trends of the hydrological cycle of the world's largest river catchment.climate change | dendrochronology | plant physiology T he Amazon basin is a major center of atmospheric convection and precipitation (1), and at the same time the world's largest drainage basin. The Amazon's river discharge accounts for ∼17% of the annual global discharge to the oceans (2); its hydrological cycle is tightly linked with the carbon cycle of the Amazon rainforest (3), which itself is one of the largest terrestrial biomass carbon pools. Changes in the hydrological cycle of the Amazon may therefore significantly affect atmospheric dynamics and global climate by changing atmospheric CO 2 concentration. Two particularly severe droughts occurred within the last decade (4), and long-term river records of the Amazon show a steady increase in discharge over the last century (5), indicating that the system may start to undergo some changes. It has been suggested that these changes are a result of anthropogenic warming, but they may also be part of longer-term, natural climatic variability. To clarify such a globally important issue, long-term, accurate records of the hydrological cycle of the Amazon basin are needed. However, meteorological data are only reliable for the last 50-60 y (6), and annually resolved long-term proxies for the hydrological cycle from within the Amazon basin itself are very scarce (7).A commonly used diagnostic for strength and functioning of the water cycle is the isotopic composition of precipitation. Although variation of oxygen isotope ratios in precip...

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Trends of upper-air circulation and water vapour over equatorial South America and adjacent oceans

Cited by 33 publications

References 25 publications

Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

The Nature and Origin of Decadal to Millennial Scale Climate Variability in the Southern Tropics of South America: The Holocene Record of Lago Umayo, Peru

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Niño-Southern Oscillation variability

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