Synoptic Analyses of the 5-, 2-, and 0.4-MILLIBAR Surfaces for the Iqsy Period (original) (raw)
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Simulations of fall and early winter in the stratosphere
Quarterly Journal of the Royal Meteorological Society, 2002
Mechanistic model simulations of fall/early winter in the northern (November-December) and southern (May-June) stratosphere are compared with observational analyses to examine the skill of the model in simulating the state of the stratosphere, including both means and variability in key fields, during six winters. While detailed success varies from year to year, the model produces a realistic climatology of and variability in the evolution of winds, geopotential heights, temperatures and wave propagation in the early winter stratosphere. The variability and mean fields agree well with those in longer data records. The NH simulations show a small cold bias when averaged over the six years, while the SH simulations show a larger warm bias. Greater detailed success in simulations of alternate NH winters suggests the possibility of greater model skill during the westerly QBO phase, although the short record and complexity of interactions between tropics and high latitudes preclude definitive identification of such a relationship. A prominent failing of the model when using Rayleigh friction to parameterize gravity-wave drag is an inability to correctly reproduce the latitudinal structure of the stratospheric jet above about 7 hPa; this failing can be alleviated by using a non-orographic gravity-wave drag parameterization, at the expense of frequently degrading agreement of planetary wave phases and amplitudes. The success of the model in reproducing realistic climatology and variability makes these simulations useful for more detailed studies of transport and vortex evolution in early winter.
International Journal of Climatology, 2003
A comparison of National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis six-hourly sea-level pressure data with former Soviet drifting station observations over the central Arctic Basin reveals high monthly correlations throughout the period 1950-91, but also a preferred winter season negative bias of about 1.4 hPa. Using the reanalysis, supplemented by Arctic Ocean Buoy Program fields and in situ observations, a generalized depiction of the annual cycle of pressure fields over the Arctic may be constructed. Above the Canada Basin-Laptev Sea side of the Arctic, the annual cycle of surface pressure is dominated by the first harmonic, which has an amplitude of about 5 hPa and maximum pressure occurring in March. Along the periphery of northern Greenland and extending to the North Pole, a weak semiannual cycle is found in surface pressure with maxima in May and November. The presence of the semiannual variation over time is highly variable.
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
Journal of atmospheric and terrestrial physics, 1990
A real-time-winds (RTW) system from Saskatoon operated with the Tromss MF (partial retlection) radar system on a continuous basis in the period JuneeDecember 1987. This interval includes MAC/SINE and EPSILON. Profiles with 3-km resolution were obtained every 5 min-weak ionization and few geomagnetic disturbances limited the observations normally to 80 I IO km. However. daily mean winds, diurnal and semidiurnal tidal characteristics (amplitudes. phases and wavelengths) and gravity wave characteristics (intensities, mean directions) are available throughout this interval. This is particularly valuable in defining the background state for some experiments, e.g. rockets, and for comparison with related parameters from the lidar and other radars (EISCAT, SOUSY-VHF). Comparisons with these dynamical parameters from Saskatoon (52 N) are made : the zonal circulation was weaker at Tromso, tidal amplitudes smaller. and summer 12-h tidal wavelengths shorter (5 80 km vs-100 km). The fall transition for this tide occurred in September at Tromso, earlier than observed clscwhcrc.
The dynamical response of the middle atmosphere to the tropospheric solar signal
Journal of Geophysical Research, 2007
To assess a possible solar modulation of the planetary waves, the 300 hPa geopotential height of the two major reanalysis data sets, NCEP/NCAR and ERA40, is studied for the difference between years of solar maximum and minimum activity for three solar cycles in the period 1963-1999. We find a significant positive difference over the North Pacific ocean for December through February which resembles that found in sea level pressures in earlier studies. Furthermore, there are statistically significant amplitude differences in the climatological state of the first two planetary waves extracted from the geopotential heights. We also perform a model study of the middle atmospheric response to the tropospheric solar signal. The 300 hPa geopotential height is used as the lower boundary in a middle atmosphere model which is run with a constant solar cycle minimum radiative forcing, so that only the lower boundary is forcing the middle atmosphere. The zonal wind and temperature at 300-0.01 hPa from the model experiment are studied in boreal winter for the same years that were studied in the geopotential height analysis. Differences of the means of the two data sets reproduce the structure and amplitude seen in observations and in reanalysis data. Whether this is a direct effect of the solar forcing of the troposphere or a feedback coupling of the solar forcing of the stratosphere is not presently clear, but the modulation of the tropospheric planetary waves seems to be important for the observed solar modulation of the stratosphere.
Longitudinal Variations of the Stratospheric Quasi-biennial Oscillation
Journal of the Atmospheric Sciences, 2004
The longitudinal dependence of interannual variations of tropical stratospheric wind is examined in a detailed general circulation model simulation and in the limited observations available. A version of the SKYHI model is run with an imposed zonally symmetric zonal momentum source that forces the zonal-mean zonal wind evolution in the tropical stratosphere to be close to an estimate of the observed zonal wind based on radiosonde observations at Singapore during the period 1978-99. This amounts to a kind of simple assimilation model in which only the zonal-mean wind field in the tropical stratosphere is assimilated, and other quantities are allowed to vary freely. A total of five experiments were run, one covering the full 1978-99 period and four for 1989-99.
Long-term Variation of Upper Stratospheric Circulation in the Northern Hemisphere in December
Journal of the Meteorological Society of Japan. Ser. II, 1990
Long-term variation of the mean zonal wind in the upper stratosphere in December is investigated using NMC geopotential height data from 1979 to 1987. The period of analysis is anteriorly extended until 1973 by combining the results of various investigators. It was found that the mean zonal wind at 1 mb, 40*N shows outstanding long-term variation of the order of 10 years. Similar variation was also found in the rocket measurement of east-west wind component at Ryori (39*N, 142*E). It is shown that the long-term variation of the mean zonal wind has a good correlation with the solar activity, ozone partial pressure and solar UV index.
Intraseasonal oscillations in the mid-latitudes: Observations, theory and GCM results
2003
Abstract We examine in this paper the role that oscillatory interactions between the jet stream and Northern Hemisphere (NH) mountain ranges play in the low-frequency variability (LFV) of the mid-latitude atmosphere. The basic observational evidence for intraseasonal oscillations in the NH extratropics is reviewed, along with the results of a hierarchy of models—from the simplest to full GCMs—that explain these observations as arising from an oscillatory topographic instability.
Doklady Earth Sciences, 2007
We have established that quasi-decadal and quasibiennial oscillations of zonal wind velocity in the equatorial stratosphere are coherent with similar oscillations of the solar activity (SA). The time lag of wind velocity oscillations at the isobaric surface 15 hPa (~28 km) relative to SA index F10.7 is approximately equal to 1 yr at both periods. During the period of SA maximum in the 1990s, coherent behavior of the equatorial stratospheric wind (ESW) and the SA was observed at all time scales from 1 to 10 yr. After a distortion in the coherency in 1994, a high coherency was observed again in 2001-2005, but with a simultaneous change of its sign at the scales of the periods of the solar cycle and quasi-biennial oscillation (QBO). The amplitudes of variations in the ESW velocity are maximal at the 15 hPa level. Quasi-decadal variations in the ESW above and below the 20-30 hPa layer are generally in opposite phase to each other. At the boundary of the 50-15 hPa layer, they are exactly in opposite phase to each other.
Dynamics of the Stratospheric Semiannual Oscillation
Journal of the Meteorological Society of Japan, 1986
This paper reports on an attempt to use observations to determine the nature of the eddy contributions to the mean zonal momentum balance in the region of the tropical stratosphere that is dominated by the semiannual oscillation (SAO). Since direct observations of the eddy wind fields in this region of the atmosphere are very limited, an indirect procedure was employed. The first step in this process was the computation of diabatic heating rates using observed temperatures and a sophisticated radiative transfer code. These heating rates were then employed to calculate the residual mean meridional circulation. The advection of mean zonal momentum and the Coriolis torque associated with the residual circulation could then be computed. The difference between this contribution to the zonal mean momentum balance and the actual observed acceleration of the zonally-averaged zonal wind was ascribed to the Eliassen-Palm (EP) flux convergence associated with eddies of all types. Meridional profiles of the inferred EP flux convergence were produced for each month of the year at the 1.0 and 0.4mb levels. At both levels there was an indication of the presence of an equatorially-trapped westerly contribution to the EP flux convergence. This is consistent with the suggestion of Hirota (1978) that the westerly accelerations in the SAO are provided by a dissipating equatorial Kelvin wave. In fact at 1mb the total EP flux convergence at the equator is always westerly; this suggests that the dominant contribution to the easterly acceleration near the equator comes from advection by the residual circulation, in accord with the model results of Holton and Wehrbein (1980) and Mahlman and Sinclair (1980). However, there is an indication of significant easterly eddy forcing of the mean flow away from the equator in the winter hemisphere (and in both hemispheres near the equinoxes). This forcing is presumably due to the equatorward propagation of planetary waves generated in the extratropics in the manner discussed by Hirota (1976, 1978, 1979). This easterly eddy forcing becomes more significant at the 0.4mb level, and the total EP flux convergence on the equator becomes easterly during the easterly acceleration phase of the SAO. It thus appears that both the Holton-Wehrbein (1980) and the Hirota (1978, 1979) mechanisms are important for the generation of the easterly accelerations in the SAO. The planetary wave contribution is most significant in the winter hemisphere and at higher levels, and the contribution from the residual circulation predominates in the summer hemisphere and at lower levels.