Sentences with phrase «annular modes»
"Annular modes" refers to patterns of climate variability in which atmospheric pressure changes occur around the Earth's poles. These changes affect the circulation of winds and weather patterns, particularly in the mid-latitude regions. The term "annular" refers to a ring-like shape or structure, as these modes typically involve a circular or elliptical pattern of pressure anomalies surrounding the poles. Full definition
Miller, R.L., G.A. Schmidt, and D.T. Shindell, 2006: Forced variations of annular modes in the 20th century IPCC AR4 simulations.
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Stammerjohn, S., et a., (2008) Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño southern oscillation and southern annular mode variability.
Annular denotes the longitudinal scale of the pattern, and annular mode suggests the NAM reflects dynamical processes that transcend a particular hemisphere or, for that matter, planet.
But there is still no single widely accepted theory as to why annular modes are so predominant in Earth's atmosphere.
In this paper we discuss the atmospheric dynamics of the North Atlantic Oscillation (NAO), the zonal index, and annular patterns of variability (also known as annular modes).
A mechanism is presented by which eddy heat and momentum transport couple to retard motion of the jet, slowing its meridional variation and thereby extending the persistence of zonal index and annular mode anomalies.
We first show that the structure of the empirical orthogonal functions (EOFs) of the NAO and annular modes follows, at least in part, from the structure of the baroclinic zone.
The characteristics of the dominant pattern of extra-tropical variability (the so - called annular modes) are examined in the context of the theory that eddy - driven jets are self - maintaining.
On monthly time scales, the southern and northern annular modes (SAM and NAM, respectively) and the North Atlantic Oscillation (NAO) are the dominant patterns of variability in the extratropics and the NAM and NAO are closely related.
These changes in atmospheric circulation are predominantly observed as «annular modes», related to the zonally averaged mid-latitude westerlies, which strengthened in most seasons from the 1960s to at least the mid-1990s, with poleward displacements of corresponding Atlantic and southern polar front jet streams and enhanced storm tracks.
The role of linear interference in the annular mode response to extratropical surface forcing.
Hall, A., and M. Visbeck, 2002: Synchronous variability in the Southern Hemisphere atmosphere, sea ice and ocean resulting from the annular mode.
His research concerns understanding global climate and its variations using observations and covers the quasi biennial oscillation, Pacific decadal oscillation and the annular modes of the Arctic oscillation and the Antarctic oscillation, and the dominant spatial patterns in month - to - month and year - to - year climate variability, including the one through which El Niño phenomenon in the tropical Pacific influences climate over North America.
The models capture the dominant extratropical patterns of variability including the Northern and Southern Annular Modes, the Pacific Decadal Oscillation, the Pacific - North American and Cold Ocean - Warm Land Patterns.
Annular Modes in the Extratropical Circulation.
The characteristics of fluctuations in the zonally averaged westerlies in the two hemispheres have more recently been described by their respective «annular modes», the Northern and Southern Annular Modes (NAM and SAM).
Trenberth et al. (2005b) analysed global atmospheric mass and found four key rotated EOF patterns: the two annular modes (SAM and NAM), a global ENSO - related pattern and a fourth closely related to the North Pacific Index and the PDO, which in turn is closely related to ENSO and the PNA pattern.
The leading mode of southern hemisphere (SH) climatic variability, the southern annular mode (SAM), has recently seen a shift towards its positive phase due to stratospheric ozone depletion and increasing greenhouse gas (GHG) concentrations.
More recent work is identifying climate shifts working through the El Niño - Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), Southern and Northern Annular Modes (SAM and NAM), Artic Oscillation (AO), Indian Ocean Dipole (IOD), North Pacific Oscillation (NPO) and other measures of ocean and atmospheric states.
Understanding the climate impacts of the annular modes has played a role in helping the climate community interpret of the structure of recent climate change, as discussed below.
However, not all aspects of the time series of the annular modes are consistent with a red - noise process with a 10 day timescale: e.g., the annular modes exhibit enhanced variability on monthly timescales during seasons of rigorous stratosphere / troposphere coupling (see section on Stratosphere / troposphere coupling, below); and both annular modes have exhibited trends over the past few decades towards their high index polarities (see section on Climate Change, below).
The impact of midlatitude sea surface temperature anomalies on the annular modes is thought to be small, at least on intraseasonal suggest interannual timescales.
In general, indices of the annular modes are based on either 1) the leading principal component (PC) time series of gridded geopotential height anomalies at a given pressure level or 2) approximations of the leading PC time series of geopotential height anomalies using differences between sea level pressure anomalies at stations in middle and high latitudes.
That said, recent evidence suggests that changes in sea - ice extent may drive variability in the annular modes.
Daily and monthly resolution indices of the annular modes are available from the NOAA CPC.
And there is good evidence that the annular modes would not exist in the absence of positive feedbacks between the induced changes in the zonal wind and the wave fluxes.
Why have the annular modes exhibited trends over the past few decades?
The changes in sea - surface temperatures are consistent with the impact of the annular modes on the surface fluxes of latent and sensible heat, and also on the flux of heat by the anomalous Ekman flow.
Observations and numerical experiments suggest the annular modes have played and will continue to play a role in climate change.
The annular modes are coupled with annular variability in the stratospheric flow during the winter season in the Northern Hemisphere and the spring season in the Southern Hemisphere.