Morphology of the Wavenumber 1 and Wavenumber 2 Stratospheric Kelvin Waves Using the Long-Term Era-Interim Reanalysis Dataset (original) (raw)
Related papers
Equatorial Kelvin wave variability during 1992 and 1993
J. Geophys. Res, 1995
Temperature and ozone data from the Microwave Limb Sounder (MLS) insmnnent on UARS are used to analyze the variability of Kelvin wave activity during the first two years of the UARS mission. The analysis is carried out using the asynoptic mapping technique. Time frequency plots for zonal wavenumbers 1 and 2, at two heights representing the middle stratosphere and the stratopause, respectively, are used to analyze the temporal variability of the waves, and its possible relationship to the equatorial quasi-biennial oscillation (QBO) and semiannual oscillation (SAO). Kelvin wave activity reaches a maximum during the solstice seasons and almost disbars during the equinoxes, in agreement with previous studies. Eastward propagating variance is estimated for wave periods from 4 to 20 days, at all UARS pressure surfaces currently available for MLS. The semiannual modulation of variance is observed to extend down to the lower limits of the height ranges of the temperalure and ozone retrievals. Furthermore, a superposed QBO modulation is detected up to the stratopause. Comparison between the variance in eastward propagating waves and the mean zonal wind shows a possible participation of kelvin waves in the forcing of the QBO. At the stratopause the role of Kelvin waves in forcing the SAO appears to be limited, in agreement with previous results. Between the 21-hPa and 4.6-hPa surfaces there appears to be a transition zone where there is no clear relationship between Kelvin wave activity and mean zonal flow acceleration.
The Annual Wave in the Temperature of the Low Stratosphere
J Atmos Sci, 1970
A quantitative examination of the annual cycle in the tropical tropopause temperatures, tropical ascent, momentum balance, and wave driving is performed using ECMWF analyses to determine how the annual cycle in tropical tropopause temperatures arises. Results show that the annual cycle in tropical tropopause temperatures is driven by the annual variation in ascent and consequent dynamical (adiabatic) cooling at the tropical tropopause. Mass divergence local to the tropical tropopause has the dominant contribution to ascent near the tropical tropopause. The annual cycle in mass divergence, and the associated meridional flow, near the tropical tropopause is driven by Eliassen-Palm (EP) flux divergence, that is, wave dissipation. The EP flux divergence near the tropical tropopause is dominated by stationary waves with both the horizontal and vertical components of the EP flux contributing. However, the largest annual cycle is in the divergence of the vertical EP flux and in particular from the contribution in the vertical flux of zonal momentum. These results do not match the existing theory that the annual cycle is driven by the wave dissipation in the extratropical stratosphere, that is, the stratospheric pump. It is suggested that the annual cycle is linked to equatorial Rossby waves forced by convective heating in the tropical troposphere.
Investigation of Kelvin Waves in the Stratosphere Using FORMOSAT-3/COSMIC Temperature Data
Journal of the Meteorological Society of Japan, 2011
Temperature data from Global Positioning System based Radio Occultation (GPS RO) soundings of the Formosa Satellite mission 3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC or F-3/C) micro satellites has been investigated in detail to study the Kelvin wave properties. The high temporal and spatial resolution satellite data from August 2006 to August 2009 have enabled the investigation of Kelvin wave activity on each day. The dominant waves of wave numbers 1 and 2 (W1 and W2) have been investigated in detail at three altitudes-19, 25 and 30 km, and it is found that the amplitude of W1 is greater than that of W2 during 60% of the time. A statistical study of the amplitudes of W1 and W2 is also presented and it is found that the dominant amplitudes are 0.5 to 1.0 K for both waves. At lower altitudes (19 km), the amplitudes of W1 are larger and the distribution is also broader. The amplitudes of both waves in the stratosphere are higher during the easterlies of the quasi-biennial oscillation (QBO) and are maximum when the zonal wind changes from easterlies to westerlies. In the lower altitudes near the tropopause they vary in consonance with the outgoing long wave radiation, a proxy of deep convection. Deduction of the Kelvin wave periods and phase velocities has been possible with better accuracy with the use of the F-3/C data. The average periods of W1 for all years are 15 G 3, 13 G 4, and 10 G 3 days at altitudes 19, 25, and 30 km, respectively and the average periods of W2 for all years are 10 G 2, 7 G 2, and 6 G 2 days, respectively. These standard deviations are geophysical and are due to the variation in the periods of the individual Kelvin wave events and identification of the period for a single Kelvin wave event is correct to within G one day. We found that the Kelvin waves of both the zonal wave numbers are slow in the lower altitudes and fast in the higher altitudes. Also, the periods decrease gradually with height. This is the most important result of the present study.
Climatology of extratropical atmospheric wave packets in the northern hemisphere
2010
Planetary and synoptic scale wave-packets represents one important component of the atmospheric large-scale circulation. These dissipative structures are able to rapidly transport eddy kinetic energy, generated locally (e.g. by baroclinic conversion), downstream along the upper tropospheric flow. The transported energy, moving faster than individual weather systems, will affect the development of the next meteorological system on the leading edge of the wave packet, creating a chain of connections between systems that can be far apart in time and space, with important implications on predictability. In this work we present a different and novel approach to investigate atmospheric variability, based on the objective recognition of planetary and synoptic wave packets. We have developed an objective tracking algorithm which allows to extract relevant statistical properties of the wave trains as a function of their dominant wavelength. We have applied the algorithm to the daily analysis (every 12h) from 1958-2009, building an extended climatology of waves packets with different spectral properties. Here we present the climatology of mean group velocity, spatial and temporal extension, initial and final longitude of wave packets, for two different and representative spectral component: wave packets composed by quasi stationary planetary waves with zonal wave number [1, 3] and wave packets composed by synoptic waves with zonal number [4, 6]. Different properties are discussed and put in relation with other atmospheric processes that might play a role in the triggering, propagation and decay of this important source of extratropical atmospheric variability.
⎯The results of analysis of variations in the sporadic layer critical frequency (foEs) for winter periods of 2008–2010 in which sudden stratospheric warmings were observed are presented in the paper. The data were obtained at Kaliningrad ionospheric station (54.6 o N, 20 o E) by a Parus digital ionosonde under the usual sounding regime with an interval of 15 min. Daily mean values of foEs were used for the analysis. Solar and geomagnetic activity remained low during the periods under study, making it possible to relate the quasi-wave time variations in foEs to the parameters of stratospheric warmings. The results of spectral analysis performed on the basis of continuous wavelet transform showed that, during all warmings occurring in 2008– 2010, time variations in foEs show the presence of wave processes with a period of an order of 5 days and longer ones with a period of ~10—11 days. These periods coincide with characteristic periods of planetary waves observed in the atmosphere during sudden stratospheric warnings.
Kelvin waves and the quasi-biennial oscillation- An observational analysis
Journal of geophysical research, 1998
A method is derived for estimating the Kelvin wave contribution to the vertical flux of westerly momentum in the equatorial stratosphere, which is based on temperature and geopotential perturbations. This method is used to estimate the momentum transfer due to Kelvin wave activity as derived from the cryogenic limb array etalon spectrophotometer (CLAES) temperature data set, for the onset of the westerly phase of the QBO during 1992 and the first few months of 1993, that is, during the first part of the Upper Atmosphere Research Satellite (UARS) mission. The results are compared with the zonal winds as observed by the high-resolution Doppler imager (HRDI) also flown on board UARS, and the United Kingdom Meteorological Office (UKMO) data assimilation model product, a correlative data set to the UARS mission. The analysis shows that although the Kelvin wave momentum flux convergence is occasionally sufficient to account for the observed QBO westerly acceleration, the observed flux is sporadic in nature and virtually disappears during the second half of the sample, when the westerly vertical shear zone approaches the 100 hPa level. An estimate of the total westerly momentum flux necessary to produce the observed descent of the westerly phase of the QBO is made using the transformed Eulerian mean (TEM) formalism. The results suggest that Kelvin waves are not sufficient to force the descent of the westerly phase of the QBO. There appears to be a need for enhanced westerly forcing throughout the descent of the westerly phase of the QBO. This enhanced forcing is most likely provided by gravity waves that are unresolved by the satellite observations. These results are in agreement with the results derived from general circulation models.
Journal of Geophysical Research, 2005
1] Equatorial Kelvin waves and ozone Kelvin waves were simulated by a T63L250 chemistry-coupled general circulation model with a high vertical resolution (300 m). The model produces a realistic quasi-biennial oscillation (QBO) and a semiannual oscillation (SAO) in the equatorial stratosphere. The QBO has a period slightly longer than 2 years, and the SAO shows rapid reversals from westerly to easterly regimes and gradual descents of westerlies. Results for the zonal wave number 1 slow and fast Kelvin waves are discussed. Structure of the waves and phase relationships between temperature and ozone perturbations coincide well with satellite observations made by LIMS, CLAES, and MLS. They are generally in phase (antiphase) in the lower (upper) stratosphere as theoretically expected. The fast Kelvin waves in the temperature and ozone are dominant in the upper stratosphere because the slow Kelvin waves are effectively filtered by the QBO westerly. In this simulation, the fast Kelvin waves encounter their critical levels in the upper stratosphere when zonal asymmetry of the SAO westerly is enhanced by an intrusion of the extratropical planetary waves. In addition to the critical level filtering effect, modulations of wave properties by background winds are evident near easterly and westerly shears associated with the QBO and SAO. Enhancement of wave amplitude in the QBO westerly shear is well coincident with radiosonde observations. Increase/decrease of vertical wavelength in the QBO easterly/westerly is obvious in this simulation, which is consistent with the linear wave theory. Shortening of wave period due to the descending QBO westerly shear zone is demonstrated for the first time. Moreover, dominant periods during the QBO westerly phase are longer than those during the QBO easterly phase for both the slow and fast Kelvin waves.
IOP Conference Series: Earth and Environmental Science, 2016
The ERA-Interim data set from Europe Center for Medium Range Weather Forecasting (ECMWF) was used to quantitatively analyze the characteristic of equatorial quasi-biennial oscillation (QBO). Analysis of spatial and temporal of the data showed that the zonally symmetric easterly and westerly phase of QBO regimes alternate with period of ~27.7 months. Based on Equivalent QBO Amplitude (EQA) method, the maximum amplitudes in zonal mean zonal wind (u), temperature (T), vertical shear (du/dz) and quadratic vertical shear (d 2 u/dz 2) are ~28.3 m/s , ~3.4 K, ~4.8 m/s/km, and ~1.0 m/s/km 2 respectively. The amplitudes decay exponentially with a Gaussian distribution in latitude. The twofold-structure of QBO descends downward at rate of ~1 km/month. The temperature anomaly can be used to analyze the characteristic of QBO which satisfies the thermal wind balance relation in the lowerstratosphere due to very small contribution of the mean meridional and vertical motion. Moreover, the concentration of the total column ozone (TCO) in the tropics is significantly influenced by QBO. During the westerly phase of QBO, the TCO is relatively increased in the lower-stratosphere, but decreased during the opposite phase.
Half-yearly wave in the stratosphere
Journal of Geophysical Research, 1972
The dominant features of the half-yearly wave in the stratospheric temperature above the 50-mb level are an amplitude peak in equatorial latitudes, the maximums being in the transition seasons, and amplitude peaks at higher latitudes of either hemisphere, the maximums being in the extreme seasons. The low-and high-latitude peaks are separated by a circumpolar belt of low values in the subtropics where the phase changes rapidly. The half-yearly wave in the zonal thermal wind, at least as high as 5 mb, reaches a peak in the subtropics where the phase in the temperature wave reverses, and the half-yearly wave in the geostrophie and the observed zonal wind above 50 mb accordingly increases poleward to latitudes of 30ø-35 ø from a minimum a few degrees north of the equator and upward. The wave in the zonal wind reaches another, but weaker, peak in the polar regions.
Kelvin Waves near the Equatorial Stratopause as Seen in SBUV Ozone Data
Journal of the Meteorological Society of Japan. Ser. II, 1991
Space-time variations of atmospheric ozone in the equatorial middle atmosphere are studied for the 8 year period 1979 to 1986, making use of the ozone mixing ratio data derived from the solar backscatter ultraviolet (SBUV) instrument on board the Nimbus-7. Analysis is made with respect to the long-term variation of the stratospheric zonal mean wind and temperature in the tropics. From a simple photochemical consideration, it is expected that ozone variations in the upper stratosphere are associated with temperature disturbances having a characteristic timescale of longer than a few days. Clear evidence is presented for the appearance of equatorially trapped ''ozone Kelvin waves" above the 10 mb level having a zonal wavenumber one component and an eastward migration period of about 7 days. Statistical results for the SBUV ozone data over 8 years shows how Kelvin wave amplitudes are closely related to the semiannual oscillation (SAO) of the zonal mean wind around the stratopause level. Further discussions are made on the effect of the quasi-biennial oscillation (QBO) of the tropical lower stratosphere on the vertical propagation of fast Kelvin waves, which in turn results in the QBO modulation of the mean field in the upper stratosphere and lower mesosphere.