The spatial and temporal behaviour of the lower stratospheric temperature over the Southern Hemisphere: the MSU view. Part II: spatial behaviour (original) (raw)
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International Journal of Climatology, 2001
The lower stratosphere monthly temperature anomalies over the Southern Hemisphere derived from soundings made by the Microwave Sounding Unit (MSU) between 1979 and 1997 are analysed. Specifically MSU channel 4 temperature retrievals are considered. Principal component (PC) analysis with the S-mode approach is used in order to isolate grid points that covary in a similar manner and to determine the main features of their temporal behaviour. The first six PCs explain 81.3% of the variance and represent the different time variability patterns observed over the Southern Hemisphere for the ten area clusters determined by the method. The most important feature is common to all the PC score pattern-time series and corresponds to a negative linear trend present in almost all the Southern Hemisphere except over New Zealand and surrounding areas. The negative trend is largest over Antarctica. The remaining features of the temporal variability are different for each PC score and therefore for each cluster region over the Southern Hemisphere. The first PC score pattern shows the impact of the Chichó n and Mt Pinatubo eruptions that each produced a 2-year warming over the tropical and sub-tropical lower stratosphere. This variability is orthogonal with the behaviour present over Antarctica. There are different anomalies between 1987 (El Niñ o) and 1988 (La Niñ a). This second PC does not show any evidence whatsoever of the volcanic eruptions. The semi-annual wave is present in the anomaly recurrence at mid to high latitudes. Over very low latitudes, close to the Equator, the Quasi-Biennial Oscillation (QBO) band of frequency is also present.
International journal of …, 2001
The lower stratosphere monthly temperature anomalies over the Southern Hemisphere derived from soundings made by the Microwave Sounding Unit (MSU) between 1979 and 1997 are analysed. Specifically MSU channel 4 temperature retrievals are considered. Principal component (PC) analysis with the S-mode approach is used in order to isolate grid points that covary in a similar manner and to determine the main features of their temporal behaviour. The first six PCs explain 81.3% of the variance and represent the different time variability patterns observed over the Southern Hemisphere for the ten area clusters determined by the method. The most important feature is common to all the PC score pattern-time series and corresponds to a negative linear trend present in almost all the Southern Hemisphere except over New Zealand and surrounding areas. The negative trend is largest over Antarctica. The remaining features of the temporal variability are different for each PC score and therefore for each cluster region over the Southern Hemisphere. The first PC score pattern shows the impact of the Chichó n and Mt Pinatubo eruptions that each produced a 2-year warming over the tropical and sub-tropical lower stratosphere. This variability is orthogonal with the behaviour present over Antarctica. There are different anomalies between 1987 (El Niñ o) and 1988 (La Niñ a). This second PC does not show any evidence whatsoever of the volcanic eruptions. The semi-annual wave is present in the anomaly recurrence at mid to high latitudes. Over very low latitudes, close to the Equator, the Quasi-Biennial Oscillation (QBO) band of frequency is also present.
Geophysical Research Letters, 2007
1] The paper presents clear evidence of zonally symmetric planetary waves with very large amplitudes present in the UK Met Office zonal wind data of the Northern Hemisphere stratosphere in the winter of 2003 -2004. The spectral analysis reveals that three prevailing periods of $23, 17 and 11 days contribute to the observed zonally symmetric oscillations. These waves are extracted from the data and their amplitudes and phases are studied in detail depending on height and latitude. The wave amplitudes -particularly those of the 11-and the 17-day zonally symmetric wavesclearly indicate the presence of two latitudinal branches of amplifications centred at 50-60°N and 20-30°N. The phase analysis shows that these waves are vertically upward propagating waves and that the waves from the high-latitude and tropical branches are almost out of phase. A possible forcing mechanism is suggested. The zonally symmetric waves play an important role in coupling the dynamical regimes of the high-and low-latitude stratosphere particularly during the major stratwarm event in the Arctic winter of 2003 -2004. Citation: Pancheva, D. V., P. J. Mukhtarov, and B. A. Andonov (2007), Zonally symmetric oscillations in the Northern Hemisphere stratosphere during the winter of
Annales Geophysicae, 2008
The coupling of the dynamical regimes in the high-and low-latitude stratosphere and mesosphere during the major SSW in the Arctic winter of 2003/2004 has been studied. The UKMO zonal wind data were used to explore the latitudinal coupling in the stratosphere, while the coupling in the mesosphere was investigated by neutral wind measurements from eleven radars situated at high, highmiddle and tropical latitudes. It was found that the inverse relationship between the variability of the zonal mean flows at high-and low-latitude stratosphere related to the SSW is produced by global-scale zonally symmetric waves. Their origin and other main features have been investigated in detail. Similar latitudinal dynamical coupling has been found for the mesosphere as well. Indirect evidence for the presence of zonally symmetric waves in the mesosphere has been found.
Theoretical and Applied Climatology, 2014
Using monthly stratospheric geopotential height at 20 hPa derived from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets, a planetary wave amplitude index (PWAI) is defined by wave numbers (WN) 1-3 over 55-75°N to indicate the strength of the stratospheric stationary waves. The vertical variability of the stratospheric stationary waves and their possible connection with the stratosphere-troposphere coupling have been investigated in the North Hemisphere winter [December-February (DJF)] for the period of 1950-2010. In terms of the stratospheric PWAI, a pair of bipolar extreme (strong and weak) stratospheric wave events is identified based on the top-ten principle. The comparisons of composite analysis for the bipolar events show that the stratospheric PWAI is an effective indicator for the dynamic coupling between the stratosphere and troposphere in the boreal winter. The results show that the opposite response in the stationary wave activity, atmospheric circulations, precipitation, and surface temperature is not only found in the stratosphere but also in the troposphere and surface. In the stratospheric top-ten extremely strong (strong10) events, the wave amplitude, poleward momentum, and heat fluxes in zonal WN1 tend to increase in the whole atmospheric layer from the stratosphere down to the surface. The polar vortex is enhanced in the stratosphere and reduced in the troposphere. Both the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO) tend to a positive phase with the sea-level pressure (SLP) decreasing in the high latitudes and increasing in the mid-low latitudes. The precipitation tends to increase in the southern Asia and decrease in the southern Europe. The surface temperature becomes warmer in the middle of the Asian-European continent and cooler in southwest Asia and south Europe. In contrast, there is a clear opposing behavior except for a few small areas during the stratospheric top-ten extremely weak (weak10) events.
Some complications in determining trends in the stratosphere
Advances in Space Research, 1991
We cannot find an unambiguous, pervasive trend in the geopotential heights and temperatures of the 25 years when reliable daily analyses of the lower stratosphere were possible. At 30 mbar the interannual variability is dominated by a low frequency wave with a period of 10-12 years. Other influences on the temperatures and heights, such as the Southern Oscillation, the QBO, volcanoes, and random variability, do not lead to trends but appear as noise superposed on the quasi-periodic, low frequency wave. Time series which begin at a peak in this wave and end in a valley naturally show a negative trend. The converse is true for series which begin in a valley and end in a peak. We conclude that several more periods of the wave are necessary before one can determine if trends of even lower frequency exist.
Journal of Atmospheric and Solar-Terrestrial Physics, 2007
The stratosphere-mesosphere response to the major sudden stratospheric warming (SSW) in the winter of 2003/2004 has been studied. The UKMO (UK Met. Office) data set was used to examine the features of the large-scale thermo-dynamic anomalies present in the stratosphere of the Northern Hemisphere. The vertical and latitudinal structure of the genuine anomalies, emphasized by removing the UKMO climatology, has been investigated as well. The features of the stratospheric anomalies have been related to the mesospheric ones in measured neutral winds from radars and temperatures from meteor radars (~90 km). It was found that the stratospheric warming spread to the lower mesosphere, while cooling occurred in the upper mesosphere, a feature which may be related to the large vertical scales of the stationary planetary waves (SPWs). It was shown also that the beginning of the eastward wind deceleration in the stratosphere/mesosphere system coincided with the maximum amplification of the SPW1 accompanied by short-lived bursts of waves 2 and 3.
Quarterly Journal of the Royal Meteorological Society, 2001
Equatorial winds in the stratosphere are known to influence the frequency of stratospheric midwinter sudden warmings. Sudden warmings, in turn, influence the Earth's climate both through their direct influence on polar temperatures and through the temperature dependence of ozone depletion in the lower stratosphere. The conventional (Holton-Tan) explanation for the equatorial influence on sudden warmings is in terms of the equatorial winds in the lower stratosphere (-20-30 km) acting as a waveguide for midlatitude planetarywave propagation. This study employs stratospheric-temperature analyses and equatorial rocketsonde wind data extending to 58 km to diagnose the relationship between the northern-hemisphere polar temperatures and equatorial zonal winds at all height levels in the stratosphere. In addition to the recognized Holton-Tan relationship linking the polar temperatures to the quasi-biennial oscillation in equatorial winds in the lower stratosphere, a strong correlation of polar temperatures with equatorial winds in the upper stratosphere is found. We suggest that this may be associated with the strength and vertical extent of the westerly phase of the semi-annual oscillation in the upper stratosphere, although the observations alone cannot provide a conclusive, causal relationship. The main diagnostic tools employed are correlation studies and composite analysis. The results underline the need for continued high quality, equatorial wind measurements at all stratospheric levels.
Classifying the tropospheric precursor patterns of sudden stratospheric warmings
Geophysical Research Letters, 2017
Classifying the tropospheric precursor patterns of sudden stratospheric warmings (SSWs) may provide insight into the different physical mechanisms of SSWs. Based on 37 major SSWs during the 1958–2014 winters in the ERA reanalysis data sets, the self‐organizing maps method is used to classify the tropospheric precursor patterns of SSWs. The cluster analysis indicates that one of the precursor patterns appears as a mixed pattern consisting of the negative‐signed Western Hemisphere circulation pattern and the positive phase of the Pacific‐North America pattern. The mixed pattern exhibits higher statistical significance as a precursor pattern of SSWs than other previously identified precursors such as the subpolar North Pacific low, Atlantic blocking, and the western Pacific pattern. Other clusters confirm northern European blocking and Gulf of Alaska blocking as precursors of SSWs. Linear interference with the climatological planetary waves provides a simple interpretation for the prec...
On the life cycle of Northern Hemisphere stratospheric sudden warming
2004
This study examines the evolution of the atmospheric flow and wave fluxes during the life cycle of a stratospheric sudden warming (SSW) in the Northern Hemisphere. Previous studies of SSWs have focused on the evolution of the flow and wave fluxes at stratospheric levels. Motivated by recent evidence of strong coupling between the circulations of the stratosphere and troposphere during the Northern Hemisphere winter, we provide here a comprehensive analysis of the evolution of the flow and wave fluxes during a SSW at levels throughout the depth of the stratosphere and troposphere. During the onset of a SSW, the polar stratosphere is disturbed by poleward heat and momentum flux anomalies associated mainly with waves of zonal wavenumber one and two. When the waves break in the lower stratosphere, they act to weaken the strength of the circumpolar flow there, and drive an anomalous mean meridional circulation that gives rise to anomalously high polar stratospheric temperatures. As the SSW progresses, the induced stratospheric circulation anomalies descend to the lower stratosphere, where they coincide with the growth of anomalous equatorward momentum fluxes by waves in the upper troposphere centered near 50°N, and by anomalous equatorward heat fluxes by waves in the lower troposphere centered near 60°N. The anomalies in tropospheric wave activity are mainly associated with waves of zonal wavenumber four and higher, and are concentrated over the Atlantic half of the hemisphere. The anomalous upper tropospheric momentum fluxes drive anomalies in the tropospheric mean meridional circulation that transport easterly zonal wind anomalies from the upper troposphere to the surface where they compose negative polarity of the Northern Hemisphere Annular Mode (NAM).