Pick interpolation, displacement equations, and W*-correspondences

100

SUMMARYA multi-year simulation with an atmospheric general-circulation model (AGCM), the Unified Model, is shown to simulate the main features of seasonal variations in the concentrations of water vapour in the stratosphere-the so-called tape-recorder signal. An off-line transport model, utilizing winds from the AGCM, is used to synthesize the signal from local contributions. During June-July-August, the most significant localized contribution to the moist phase of the signal comes from an air stream emanating from the South-East Asian monsoon. The moist air does not enter the stratosphere immediately above the monsoon in a localized 'fountain'. Rather, the air stream moves southward, via the monsoon's upper level anticyclone, into the tropical stratosphere while moving steadily upwards across isentropic surfaces in a field of radiative heating in the tropical tropopause layer (TTL). As a result of this steady ascent during equatorward movement, not all the airstream is freeze dried in the cold cap of low temperatures which exists in the TTL above the monsoon. The water vapour mixing ratios of air entering the stratospheric tape-recorder are therefore not entirely set by the minimum temperatures near the equator, but in part by physical conditions outside the inner tropical region used to define the tape-recorder signal. During December-January-February, the flow near the tropopause is simpler. Dry air enters the stratosphere by slow upglide through the localized temperature minimum near the tropical tropopause over the western Pacific. The mixing ratios during the dry phase are set largely by freeze drying in this region. The simple tape-recorder model, which envisages that mixing ratios are set by the minimum temperature near the tropical tropopause is therefore an oversimplification.

Section: Discussion Of the 'Dry' Phasementioning

confidence: 99%

The role of the south‐east Asian monsoon and other seasonal features in creating the ‘tape‐recorder’ signal in the Unified Model

Bannister

O’Neill

Gregory

et al. 2004

100

“…Fig. 3; see also Norton andCarver 1994 andNash et al 1996), it is difficult to say anything conclusive about the variation of vortex area with height from these plots or the elliptical diagnostics. Figure 12 shows the temporal variation of qc, A,, 6, and 6 on each isentropic surface during the above period.…”

Section: Vertical Structurementioning

confidence: 95%

“…These 'elliptical' diagnostics define the area, centre, aspect ratio and orientation of the polar vortex, and hence enable the movement and elongation of the vortex to be quantified. Although the area diagnostic is sensitive to the contour used to define the vortex (see also Norton andCarver 1994 andNash et al 1996), the other diagnostics are not for contours within the vortex-edge region. By examining the variations of these elliptical diagnostics with time and altitude, the temporal evolution and vertical structure of the polar vortices can be quantified.…”

Section: Concluding Remarks and Future Workmentioning

confidence: 99%

Elliptical diagnostics of stratospheric polar vortices

Waugh

1997

Diagnostics based on the spatial moments of isopleths of a long‐lived tracer, or of potential vorticity, are presented that enable the structure and evolution of stratospheric polar vortices to be concisely summarized and quantified. The area, centre, aspect ratio and orientation of the ‘equivalent ellipse’ of the vortex, on an isentropic surface, are defined using the second‐ and lower‐order spatial moments of contours within the vortex‐edge region. By examining the variations of these ‘elliptical’ diagnostics with time and altitude, the temporal evolution and vertical structure of the polar vortices can be quantified. The usefulness of the diagnostics is assessed by examining nitrous oxide data from the Geophysical Fluid Dynamics Laboratory ‘SKYHI’ general‐circulation model. The diagnostics show, and quantify, several differences between the Arctic and Antarctic vortices in the SKYHI model. The Arctic vortex moves further off the pole, is generally more elongated, and has a more complicated vertical structure than the Antarctic vortex (with larger variations of both the vortex centre and elongation with height). The elliptical diagnostics also identify the occurrence of large‐scale Rossby‐wave breaking events, both at the vortex edge and in the subtropics, in the model.

“…This has limited application for forecasting, where the transient response of the troposphere to an imposed stratospheric change is required. Arguably, the experiments of Polvani and Kushner (2002) and Norton (2003) are more suited to studies of the response of the troposphere to changes to the stratosphere under climate change, such as the experiments of Shindell et al (1999) and Gillett et al (2002), who investigated the tropospheric response to increase in greenhouse gas concentrations and ozone depletion.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of tropospheric forecasts to stratospheric initial conditions

Charlton

O’Neill

Lahoz

et al. 2004

SUMMARYA number of recent papers in the atmospheric science literature have suggested that a dynamical link exists between the stratosphere and troposphere. Numerical modelling studies have shown that the troposphere has a time-mean response to changes to the stratospheric climatological state. In this study the response of the troposphere to an imposed transient stratospheric change is examined.The study uses a high horizontal and vertical resolution numerical weather-prediction model. Experiments compare the tropospheric forecasts of two medium-range forecast ensembles which have identical tropospheric initial conditions and different stratospheric initial conditions. In three case studies described here, stratospheric initial conditions have a statistically significant impact on the tropospheric flow. The mechanism for this change involves, in its most basic step, a change to tropospheric synoptic-scale systems. A consistent change to the tropospheric synoptic-scale systems occurs in response to the stratospheric initial conditions. The aggregated impact of changes to individual synoptic systems maps strongly onto the structure of the Arctic Oscillation, particularly over the North Atlantic storm track. The relationship between the stratosphere and troposphere, while apparent in Arctic Oscillation diagnostics, does not occur on coherent, hemispheric scales.