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Karin Labitzke

Abstract

The interannual variability of the stratosphere in the northern winter is discussed, mainly on the basis of zonal harmonic wave analyses of the daily height and temperature fields in the middle stratosphere. Comparing 12 winters, common and distinctive characteristics of the midwinter disturbances have been evaluated and three types of midwinter warmings have been identified.

It is shown that the main difference between disturbed and undisturbed winter months in the middle stratosphere lies in the different development of zonal harmonic wave 2, and that the development and vertical extent of this wave depend on the vertical structure of the cold trough over Canada.

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Karin Labitzke

Abstract

The development in time and space of the planetary-scale height waves 1 and 2 and of the mean zonal flow is described for the winter 1978/79. It is concluded that this winter supports earlier observational results: the anomalous amplification of height wave 1 in the stratosphere concurrent with a distinct minimum of height wave 2 is a characteristic precondition for the development of a major warming. If, later, the breakdown itself concurs with the development of height wave 2, the amplification of height wave 1 before is needed insofar as it changes the zonal flow, i.e., displaces the stratospheric jet poleward, to favor propagation of height wave 2.

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Karin Labitzke

Abstract

The midwinter temperature changes of the mesosphere and stratosphere are described by means of Satellite Infrared Spectrometer and Selective Chopper Radiometer data, rocketsondes, and rocket grenade data, which show that the so-called stratospheric midwinter warmings extend at least into the upper mesosphere. Temperature changes of opposite sign take place at the same time at different levels, probably as a result of vertical motion. The event begins around a very high stratopause, ∼60 km, which descends 20 km within several days while the warming intensifies. At the same time the upper mesosphere and lower stratosphere cool. When the polar vortex breaks down, the warming reaches the lower stratosphere, the warm stratopause region is destroyed through cooling of the layer between 30 and 60 km, and the upper mesosphere warms.

The mean vertical temperature profiles suggest that the upper mesosphere is cold at high latitudes in early winter and again in late winter, and that the warm upper mesosphere observed in late January–early February is associated with the breakdown of the stratospheric polar vortex.

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Karin Labitzke

Abstract

An investigation of tropospheric conditions before and after pronounced stratospheric midwinter warmings indicates an interdependence of developments in the two atmospheric regions.

The eleven northern hemisphere winters which have been investigated show that every two years the behavior of the stratosphere is similar as regards the location of the initial warming, direction of movement of systems, and subsequent response of the troposphere.

Every second year the midwinter warmings begin in the stratosphere above the eastern United States and Canada, as illustrated in the published examples from 1957 and 1963.

During the alternate years of the cycle the warmings originate over central and eastern Europe. In this paper the emphasis has been placed on this type of warming. The tropospheric circulation patterns before each warming of this kind are analogous, and the warming is followed after about ten days by a blocking situation at sea level.

It is likely that there is a connection between the 26-month cycle in the stratospheric winds in the tropics and the cycle in the stratospheric warnings.

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Harry Van Loon and Karin Labitzke

Abstract

Sea level pressure, surface air temperature, and 700-mb temperature and geopotential height show a probable association with the 11-year solar cycle which can be observed only if the data are divided according to the phase of the Quasi-Biennial Oscillation. The range of the response is as large as the interannual variability of the given element, and the correlations prove statistically meaningful when tested by Monte Carlo techniques. The sign of the correlations changes over the hemisphere on the spatial scale of extensive teleconnections. The correlations at 700 mb tend to be of opposite sign in the east and west years of the QBO, a result which Labitzke and van Loon also found in an analysis of the stratosphere. The pattern of correlation between the 700-mb heights on the Northern Hemisphere and the solar flux is the same as that of point-to-point correlations (teleconnections) between the 700-mb height at selected points and the heights at all other points. We interpret this similarity as a property of the atmosphere's internal dynamics, a favored resonance evoked within the atmosphere itself or by extraneous effects.

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Karin Labitzke and Harry Van Loon

Abstract

The probable association in the northern winter between the atmosphere and the 11-yr solar cycle extends to the frequency of lows in the North American east coast trough and thus adds a synoptic aspect to the previously described atmospheric variability on the 11-yr time scale. Statistically significant correlations of sea level pressure, 700-mb height, and surface air temperature on the Northern Hemisphere in July–August with the 11-yr solar cycle are found primarily over the oceans. The few years for which data of sea level pressure at grid points are available an the Southern Hemisphere yield coherent correlation patterns in summer and winter which are especially marked in the East years of the QBO. The temperature in the lower stratosphere over the South Pole in spring is well correlated with the solar activity in the East and hardly at all in the West years of the QBO. On the Northern Hemisphere the West years in spring are as strongly correlated with the solar cycle in the stratosphere as they are in winter. The pattern of positive and negative correlations is, however, the opposite of that in winter, which we interpret as being related to the different time of occurrence of the final warming in years with or without major midwinter warmings.

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Kirstin Krüger, Barbara Naujokat, and Karin Labitzke

Abstract

A strong midwinter warming occurred in the Southern Hemisphere (SH) stratosphere in September 2002. Based on experiences from the Northern Hemisphere (NH), this event can be defined as a major warming with a breakdown of the polar vortex in midwinter, which has never been detected so far in the SH since observations began at the earliest in the 1940s. Minor midwinter warmings occasionally occurred in the SH, but a strong interannual variability, as is present in winter and spring in the NH, has been explicitly associated with the spring reversals.

A detailed analysis of this winter reveals the dominant role of eastward-traveling waves and their interaction with quasi-stationary planetary waves forced in the troposphere. Such wave forcing, finally leading to the sudden breakdown of the vortex, is a familiar feature of the northern winter stratosphere. Therefore, the unusual development of this Antarctic winter is described in the context of more than 50 Arctic winters, concentrating on winters with similar wave perturbations. The relevance of preconditioning of major warmings by traveling and quasi-stationary planetary waves is discussed for both hemispheres.

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Paul R. Julian and Karin B. Labitzke

Abstract

The spectral energy equations for zonal and eddy kinetic and available potential energies are used to investigate the energetics of the lowest 30 km of the atmosphere during the months of January and February 1963. A major stratospheric warming, manifested in the reversal of the stratospheric meridional temperature gradient and destruction of the polar-night stratospheric vortex, began in mid-January.

Data for eight standard pressure levels, from 850 to 10 mb, for every fifth day were utilized. The horizontal wind field was estimated by using both the geostrophic approximation and a modified stream function. The vertical motion field (dp/dt) was estimated both by the adiabatic technique and by the solution of the omega equation.

The variation of the energy exchanges with height (pressure) indicates that the lower and middle troposphere and the middle stratosphere were baroclinically active regions before and during the warming. The principal path of energy flow in these regions was from zonal to eddy available potential energy, from there to eddy kinetic energy and thence to zonal kinetic energy. After the reversal of the meridional temperature gradient, however, the portion of the stratosphere studied rapidly lost eddy kinetic energy to other forms of energy. At all times eddy kinetic energy was supplied to the stratosphere by the upward flux of mechanical energy from the troposphere.

The upper troposphere and lower stratosphere appear, as a whole, to contribute little to the net energy changes both before and after the warming. Barotropic effects are suggested, however, since the principal energy exchange in this region is from zonal to eddy kinetic energy. The upward flux of energy from the troposphere to the stratosphere is large compared with the energy exchange processes occurring in the stratosphere and must be considered a significant item in the budget of the stratosphere.

A relationship between high-latitude blocking in the troposphere and the onset of the stratospheric warming is shown by comparing the variation of the 500-mb zonal wind with latitude and time with the average absolute vertical motion (dp/dt) for a mid-tropospheric and a mid-stratospheric level. Increased vigor of the vertical motion field accompanies both the onset of blocking in the troposphere and the warming in the stratosphere. Some speculation is offered concerning the interpretation of this relationship as it pertains to the cause of the stratospheric warmings.

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Harry van Loon, Karin Labitzke, and Roy L. Jenne

Abstract

This note deals with the standard deviations of 24-hr changes in 10-mb temperatures and heights. The standard deviations are differently distributed in disturbed and in quiet winter months. In the disturbed months their largest values form a coherent area at high latitudes; in the quiet months they surround the polar region as a ring with its center on the Atlantic side.

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William Randel, Petra Udelhofen, Eric Fleming, Marvin Geller, Mel Gelman, Kevin Hamilton, David Karoly, Dave Ortland, Steve Pawson, Richard Swinbank, Fei Wu, Mark Baldwin, Marie-Lise Chanin, Philippe Keckhut, Karin Labitzke, Ellis Remsberg, Adrian Simmons, and Dong Wu

Abstract

An updated assessment of uncertainties in “observed” climatological winds and temperatures in the middle atmosphere (over altitudes ∼10–80 km) is provided by detailed intercomparisons of contemporary and historic datasets. These datasets include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements. The comparisons focus on a few basic circulation statistics (temperatures and zonal winds), with special attention given to tropical variability. Notable differences are found between analyses for temperatures near the tropical tropopause and polar lower stratosphere, temperatures near the global stratopause, and zonal winds throughout the Tropics. Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere. Detailed comparisons of the tropical semiannual oscillation (SAO) and quasi- biennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data.

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