Showing papers on "Climate oscillation published in 1998"

Interactions between the atmosphere and terrestrial ecosystems: influence on weather and climate

Abstract: This paper overviews the short-term (biophysical) and long-term (out to around 100 year timescales; biogeochemical and biogeographical) influences of the land surface on weather and climate. From our review of the literature, the evidence is convincing that terrestrial ecosystem dynamics on these timescales significantly influence atmospheric processes. In studies of past and possible future climate change, terrestrial ecosystem dynamics are as important as changes in atmospheric dynamics and composition, ocean circulation, ice sheet extent, and orbit perturbations.

North Atlantic Oscillation Dynamics Recorded in Greenland Ice Cores

Abstract: Carefully selected ice core data from Greenland can be used to reconstruct an annual proxy North Atlantic oscillation (NAO) index This index for the past 350 years indicates that the NAO is an intermittent climate oscillation with temporally active (coherent) and passive (incoherent) phases No indication for a single, persistent, multiannual NAO frequency is found In active phases, most of the energy is located in the frequency band with periods less than about 15 years In addition, variability on time scales of 80 to 90 years has been observed since the mid-19th century

A Decadal Climate Cycle in the North Atlantic Ocean as Simulated by the ECHO Coupled GCM

Abstract: In this paper a decadal climate cycle in the North Atlantic that was derived from an extended-range integration with a coupled ocean–atmosphere general circulation model is described. The decadal mode shares many features with the observed decadal variability in the North Atlantic. The period of the simulated oscillation, however, is somewhat longer than that estimated from observations. While the observations indicate a period of about 12 yr, the coupled model simulation yields a period of about 17 yr. The cyclic nature of the decadal variability implies some inherent predictability at these timescales. The decadal mode is based on unstable air–sea interactions and must be therefore regarded as an inherently coupled mode. It involves the subtropical gyre and the North Atlantic oscillation. The memory of the coupled system, however, resides in the ocean and is related to horizontal advection and to the oceanic adjustment to low-frequency wind stress curl variations. In particular, it is found that variations in the intensity of the Gulf Stream and its extension are crucial to the oscillation. Although differing in details, the North Atlantic decadal mode and the North Pacific mode described by M. Latif and T. P. Barnett are based on the same fundamental mechanism: a feedback loop between the wind driven subtropical gyre and the extratropical atmospheric circulation.

Millennial-scale climate instability during the early Pleistocene epoch

Abstract: Climate-proxy records of the past 100,000 years show that the Earth's climate has varied significantly and continuously on timescales as short as a few thousand years (1–7). Similar variability has also recently been observed for the interval 340–500 thousand years ago8. These dramatic climate shifts, expressed most strongly in the North Atlantic region, may be linked to — and possibly amplified by — alterations in the mode of ocean thermohaline circulation4,5,6,7,8,9. Here we use sediment records of past iceberg discharge and deep-water chemistry to show that such millennial-scale oscillations in climate occurred over one million years ago. This was a time of significantly different climate boundary conditions; not only was the early Pleistocene epoch generally warmer, but global climate variations were governed largely by changes in Earth's orbital obliguity. Our results suggest that such millennial-scale climate instability may be a pervasive and long-term characteristic of Earth's climate, rather than just a feature of the strong glacial–interglacial cycles of the past 800,000 years.

Decadal climate oscillations in the Arctic: A new feedback loop for atmosphere‐ice‐ocean interactions

Abstract: A combined complex empirical orthogonal function analysis of 40 years of annual sea ice concentration (SIC) and winter sea level pressure (SLP) data reveals the existence of an approximately 10-year climate cycle in the Arctic and subarctic. The cycle is characterized by a clockwise propagating signal in the SIC anomalies and a standing oscillation in the SLP anomalies, the latter being linked to a fluctuation between the two phases of the North Atlantic Oscillation. To describe the formation and evolution of the SIC and SLP anomalies associated with the cycle, a simple feedback loop is proposed.

A pan‐Atlantic decadal climate oscillation

Abstract: Sea surface temperature (SST) variabilities on time scales of 10–14 years have been documented in various parts of the Atlantic Ocean. Here we present observational evidence that these regional variabilities are part of a coherent pan-Atlantic decadal oscillation (PADO) characterized by zonal bands of SST and wind anomalies stacked in the meridional direction with alternate polarities from the South Atlantic all the way to Greenland. We propose that the interaction of wind, evaporation and SST is key to establishing this interhemispherical PADO, based on results from a new ocean-atmosphere coupling model. Forced by extratropical wind forcing, the model successfully reproduces the observed decadal oscillation in both SST and wind velocity over the Tropics. This decadal extratropical forcing of the Tropics is in sharp contrast to the well-known Tropics-to-extratropics teleconnection that operates on interannual time scales in association with El Nino/Southern Oscillation (ENSO).

Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region

Abstract: Direct human influences on climate have been detected at local scales, such as urban temperature increases and precipitation enhancement1,2,3, and at global scales4,5. A possible indication of an anthropogenic effect on regional climate is by identification of equivalent weekly cycles in climate and pollution variables. Weekly cycles have been observed in both global surface temperature6 and local pollution7 data sets. Here we describe statistical analyses that reveal weekly cycles in three independent regional-scale coastal Atlantic data sets: lower-troposphere pollution, precipitation and tropical cyclones. Three atmospheric monitoring stations record minimum concentrations of ozone and carbon monoxide early in the week, while highest concentrations are observed later in the week. This air-pollution cycle corresponds to observed weekly variability in regional rainfall and tropical cyclones. Specifically, satellite-based precipitation estimates indicate that near-coastal ocean areas receive significantly more precipitation at weekends than on weekdays. Near-coastal tropical cyclones have, on average, significantly weaker surface winds, higher surface pressure and higher frequency at weekends. Although our statistical findings limit the identification of cause–effect relationships, we advance the hypothesis that the thermal influence of pollution-derived aerosols on storms may drive these weekly climate cycles.

Sea Floor Records Reveal Interglacial Climate Cycles

Abstract: CLIMATEResearchers studying deep deposits of muck on the sea floor have now read a detailed history of climate that extends nearly 2 million years into the past and covers multiple interglacial periods. As one group reports in this issue of Science (p. [1335][1]), the record shows that global climate varies on regular cycles lasting from 1200 to 6000 years, in glacial and interglacial periods alike. It's a finding that offers a mixed message of reassurance and warning about the future of our own climate as greenhouse gases warm the world. [1]: http://www.sciencemag.org/cgi/content/short/279/5355/1335

The problems and progress in the studies of mechanisms for quaternary climate changes

Abstract: Since 1950's when Emiliani obtained the first curve of the oxygen isotope records in the deep ocean sediments, the classical glaciation hypothesis developed by Penck had been replaced by the new discoveries which, by the works of Emiliani and of Shakeleton, demonstrated that during Quaternary period the cycles of glacial interglacial were much more than four times. The correspondence between the paleoclimate records from deep ocean sediments as well as continental loess and the earth orbital parameters have established a solid framework for the study of climate change mechanisms. In recent years, the new discoveries including climatic instability during last glacial period have provided an opportunity to study the characteristics and mechanisms of the millennial scale climate changes. However, paleoclimatologists are still puzzled by the climate change mechanisms concerning the devolopment of glacial interglacial cycles, the symchronic climate changes between Northern and Southern Hemisphere, and the operation of the climate instability.

Comment [on “Unknowns about climate variability render treaty targets premature”]

Abstract: In a recent Forum piece that discusses climate variability (Eos, December 16, 1997), S. F. Singer claims that “a higher CO2 level may be less dangerous to the climate system than a lower one.” The basis for this reasoning is the observation that during the last Ice Age, CO2 levels (∼200 ppmV) were lower than pre-Industrial Revolution Holocene levels (∼280 ppmV), yet the climate system was apparently more unstable than during the Holocene. Singer neglects to add that, in addition to CO2, other Ice Age global boundary conditions were very different from today's, notably larger continental ice sheets in the Northern Hemisphere, higher levels of aerosols, and colder sea-surface temperatures. Climatic variations associated with these boundary conditions are not completely understood, but clearly singling out CO2 grossly oversimplifies the complexity of the climate system and the underlying causes of climate variability.