Karin Labitzke

Associations between the 11-year solar cycle, the QBO and the atmosphere. Part I: the troposphere and stratosphere in the northern hemisphere in winter

Abstract Linear correlations between the three solar cycles in the period 1956–1987 and high-latitude stratospheric temperatures and geopotential heights show no associations. However, when the data are stratified according to the east or west phase of the quasi-biennial-oscillation (QBO) in the equatorial stratosphere significant correlations result: when the QBO was in its west phase the polar data were positively correlated with the solar cycle while those in middle and low latitudes were negatively correlated. The converse holds for the east phase of the QBO. Marked relationships existed throughout the troposphere too. No major mid-winter warming occurred in the west phase of the QBO during a minimum in the three solar cycles. In the east phase major warmings tended to take place in the minima of the cycle. Thus the signal of the quasi-biennial-oscillation in the extratropical stratosphere tends to be strengthened in solar minima, and weakened in solar maxima.

The SPARC Intercomparison of Middle-Atmosphere Climatologies

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include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements.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 Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere.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 quasibiennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data.

Stratospheric temperature increases due to Pinatubo aerosols

Northern hemisphere stratospheric temperatures at 30 and 50 mb beginning in June 1991 are compared with 20-year (1965–1984) and 26-year (1964–1989) monthly means. Significant temperature increases are shown in July, August, September, and October for latitudes from approximately 30°N to the equator. In September and October, +2σ to +3σ deviations are observed for large areas between the equator and 30°N, with temperature increases as high as +3.5°C occurring at some locations. The monthly averaged zonal mean 30-mb temperatures at 20°N in September and October were approximately 2.5°C higher than the 26-year mean, with some daily zonal mean increases of almost 3°C. Higher values occurred equatorward of 20°N. We believe these warmings are due to absorption of radiation by the new aerosols produced from the June eruptions of the volcano Pinatubo (15.1°N, 120.4°E) in the Philippines. We also expect stratospheric warmings to be occurring simultaneously at southern latitudes, especially from the equator to about 20°S, based on satellite and lidar measurements of the locations of the new aerosol layers. These localized temperature increases should decrease in magnitude and become more global as the cloud disperses globally and spreads in altitude.

The Southern Oscillation. Part V: The Anomalies in the Lower Stratosphere of the Northern Hemisphere in Winter and a Comparison with the Quasi-Biennial Oscillation

Abstract The mean anomalies of 50 mb height in the northern winter for seven Warm Events in the Southern Oscillation show a weak polar vortex and an enhanced Aleutian high. In the mean for six Cold Events the polar vortex is unusually strong and the Aleutian high is weakened and displaced far to the southwest. These anomalies are consistent with the corresponding anomalies in sea level pressure pattern. The Warm Events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense. These events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high. In other Warm Events the temperature of the tropical stratosphere was abnormally low. The mean anomalies of the Quasi-Biennial Oscillation for the winter as a whole (west minus east phase) computed from years with no Cold or Warm Events are zonally symmetrical and shaped as four concentric regions with alternatin...

Improved 11‐year solar signal in the Freie Universität Berlin Climate Middle Atmosphere Model (FUB‐CMAM)

So far, general circulation model studies have not been able to capture the magnitude and characteristics of the observed 11-year solar signal in the stratosphere satisfactorily. Here results from model experiments with the Freie Universitat Berlin Climate Middle Atmosphere Model are presented that are in considerable agreement with observations. The experiments used realistic spectral solar irradiance changes, ozone changes from a two-dimensional radiative-chemical-transport model, and a relaxation toward observed equatorial wind profiles throughout the stratosphere. During Northern Hemisphere winter a realistic poleward downward propagation of the polar night jet (PNJ) anomalies, significantly weaker planetary wave activity, and a weaker mean meridional circulation under solar maximum conditions are reproduced in the model. The observed interaction between the Sun and the Quasi-Biennial Oscillation (QBO) is captured and stratospheric warmings occur preferentially in the west phase of the QBO. Only the magnitude of the anomalies during the dynamically active season improves, whereas the summer signal and the signal at low latitudes are still too weak. The results emphasize the important role of equatorial winds in achieving a more realistic solar signal by producing a more realistic wind climatology. Furthermore, they confirm recent results that equatorial winds in the upper stratosphere, the region dominated by the Semiannual Oscillation, are an important factor in determining interannual variability of the PNJ.

Temperature Changes in the Mesosphere and Stratosphere Connected with Circulation Changes in Winter

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 mesospher...

Interannual Variability of the Winter Stratosphere in the Northern Hemisphere

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.

Association between the 11-Year Solar Cycle, the QBO, and the Atmosphere. Part II: Surface and 700 mb in the Northern Hemisphere in Winter

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 ...

An investigation of dynamical contributions to midlatitude ozone trends in winter

On timescales less than a month, negative (positive) 100 hPa temperature anomalies (deviations from seasonal means) and positive (negative) 100 hPa height anomalies at northern midlatitudes are associated with negative (positive) total ozone anomalies owing to vertical and horizontal advective transport of ozone. We apply linear regression relationships between total ozone and 100 hPa temperature and height together with observed monthly temperature and height anomalies to estimate the component of total ozone variability at northern midlatitudes that results from month-to-month differences in advective transport. At 45°N, this empirical method simulates a large part of the observed monthly zonal mean total ozone variability over the period 1979 - 1991. In order to estimate the advective transport contribution to total ozone trends, we apply a multiple regression statistical model to empirical model time series for latitudes of 10°N to 60°N. These empirical model trends result from long-term changes in ozone advective transport which are calculated on a month-to-month basis. The resulting model trend component at northern midlatitudes in February has a longitude dependence consistent with that of the observed ozone trends and has a latitude dependence that also agrees with that of the observed trends, peaking at midlatitudes and decreasing at higher latitudes. Subtracting the estimated advective contribution from the observed trends yields a residual meridional trend profile that agrees more closely in latitude dependence and amplitude with two-dimensional stratospheric model estimates.

Sunspots, the QBO and the stratosphere in the North Polar Region - 20 years later

We have shown in earlier studies the size of the changes in the lower stratosphere which can be attributed to the 11-year sunspot cycle (SSC). We showed further that in order to detect the solar signal it is necessary to group the data according to the phase of the Quasi-Biennial Oscillation (QBO). Although this is valid throughout the year it was always obvious that the effect of the SSC and the QBO on the stratosphere was largest during the northern winters (January/February). Here we extend our first study (LABITZKE, 1987) by using additional data. Instead of 30 years of data, we now have 65 years. Results for the entire data set fully confirm the early findings and suggest a significant effect of the SSC on the strength of the stratospheric polar vortex and the mean meridional circulation.