J. R. Ziemke

Kelvin waves in total column ozone

Tropical Kelvin waves have been observed previously in ozone mixing ratio data from the SBUV (Solar Backscatter Ultraviolet) and LIMS (Limb Infrared Monitor of the Stratosphere) instruments on board the Nimbus-7 satellite. The present study investigates Kelvin wave features in total column ozone, using version 6 data from the Total Ozone Mapping Spectrometer (TOMS) instrument (also on Nimbus-7). Results show eastward-propagating zonal waves 1–2 with periods ∼5–15 days, amplitudes ∼3–5 Dobson Units (1–2% of the time mean), and latitudinal symmetry typical of Kelvin waves. The analyses and a linear model in this study suggest that the primary source of the perturbations is slow Kelvin waves in the lower-to-middle stratosphere. Maximum Kelvin wave signatures occur in conjunction with westward lower-to-middle stratospheric equatorial zonal winds [a quasi-biennial oscillation (QBO) wind modulation effect]. The significance of these results is that the TOMS data are shown to be useful for investigations with global coverage of a major component of tropical stratospheric dynamics, Kelvin waves. The TOMS data set with its excellent coverage and high quality should be useful in validating model studies in the relatively data sparse and dynamically difficult tropical region.

Quasi-biennial oscillation and tropical waves in total ozone

Westward and eastward propagating tropical waves in total ozone are investigated in 13 years (1979–1991) of version 6 total column ozone data from the Nimbus 7 total ozone mapping spectrometer (TOMS) satellite instrument. A clear synchronization between the stratospheric quasi-biennial oscillation (QBO) zonal winds and the fast (periods < 15 days) propagating waves in tropical TOMS data is detailed. Largest total ozone wave amplitudes (∼3–6 Dobson units) occur when their phase propagation direction is primarily opposite the Singapore QBO lower-stratospheric winds. This effect is most apparent in meridionally symmetric components. Examination of specific episodes, including cross-spectral calculations with Singapore rawinsonde wind data (10–70 hPa), reveals signatures of tropically confined eastward propagating Kelvin waves of zonal wavenumbers 1–2 during the descending eastward QBO phase, consistent with acceleration of that QBO phase by Kelvin waves. The TOMS results are also consistent with possible forcing of the westward QBO wind phase by episodes of both meridionally symmetric and asymmetric westward waves (W events in the text). However, in contrast to the case of eastward (Kelvin) waves the strongest westward events (W events in the text) appear to be filtered by, rather than forcing, the westward phase of the stratospheric QBO wind. These dominant westward episodes are interpreted as meridionally symmetric westward global normal modes and tropically confined equatorial-Rossby waves 2–6. The events exhibit phase and group speeds characteristic of wave dynamics rather than simple wind advection. These results underscore the utility of the long time series and excellent horizontal coverage of TOMS data for dynamical investigations in the relatively observation-poor tropical stratosphere.

One-to-Two Month Oscillations: Observed High-Latitude Tropospheric and Stratospheric Response to Tropical Forcing

Abstract Careful spectral, correlation and coherence analyses of low-frequency fluctuations in global geopotential height data are presented. Attention is paid to proper statistical assessments. The main points are: 1) one-to-two month oscillating quasi-stationary wavetrains have recently been reported in the extratropical Southern Hemisphere troposphere, as far south as the edge of Antarctica. However, only weak correlations were observed with the supposed tropical forcing region, leading to the question of whether the wavetrain is a response to tropical forcing or possibly due to in situ instabilities on 1–2 month time scales. The present paper clears up this enigma with analyses of other tropical datasets which reveal clear correlation between low latitude source regions and the SH extratropical troposphere. 2) An earlier investigation found strong correlations between 1–2 month oscillations in the upper stratosphere and tropical troposphere, yet no vertical propagation was found directly above the tro...

Stratospheric circulation features deduced from SAMS constituent data

Abstract Stratospheric circulation is investigated by further analyses of three years of Stratospheric And Mesospheric Sounder (SAMS) data. Eddy effects on constituent transport are investigated with two transport formulations the transformed Eulerian mean formulation and the effective transport formulation. The transformed Eulerian mean formulation, together with calculated residual mean winds (v*, w*), is used to delineate regions, or times, of significant eddy contributions to constituent transport. Significant regions are found in the stratosphere in all seasons, not only in the Northern Hemisphere (NH) winter high latitudes (where contributions from nonlinear and nonsteady perturbations in sudden and final warming events are expected), but also in the midlatitude, middle stratosphere in autumn and at winter-summer low latitudes near the stratopause. Questionably large calculated ρ0−1Δ · M magnitudes near the stratopause during solstice suggest that the use of residual winds calculated here may be i...

One-to-Two Month Oscillations in the Stratosphere during Southern Winter

Abstract Stratospheric disturbances on the 35–60 day time scale are investigated with particular emphasis on the Southern Hemisphere. The data used are stratospheric brightness temperatures from 90 to 1.5 hPa covering seven 6-month southern winter periods (from April 1980 to March 1987). Global time-lag correlation plots are constructed from which tropical/extratropical connections, three-dimensional wave structure, and propagation characteristics are studied. Horizontal correlation patterns at 90 hPa reveal a strong connection between the Indonesian tropics and the winter extratropics. Vertical correlation patterns in the southern winter extratropics reveal westward tilt with height and vertical propagation of 35–60 day zonal wavenumber 1 perturbations, from tropospheric regions up to great heights, at least as high as the stratopause region. Disturbances are found to propagate from 90 hPa to 1.5 hPa in generally 6 to 9 days. In contrast, the vertical correlation plots in the tropics indicate little or n...

A practical method for predicting midlatitude total column ozone from operational forecast temperature fields

Accurate forecasts of total column ozone (Ω) are important because, among other reasons, forecasts of clear-air biologically important solar ultraviolet (UVB) reaching the Earths surface are exponentially sensitive to Ω. We present a simple method for predicting Ω using forecast lower stratospheric temperatures and a precalculated lookup table based on ozone climatology from several years of satellite observations. Compared with observations, the simple method gives 1-day forecast Ω errors of ∼1–2% (∼2–3%) in northern (southern) hemisphere summers, comparable with current multivariate UVB forecast models being used by national weather services in several countries. The advantage of the prediction method described here is its simplicity: a convenient lookup table based on ozone climatology is used, without the need for recalculation in each forecast. The method may prove useful for surface UVB forecasts, especially in the biologically important summer seasons of both hemispheres.

Space‐time integrity of improved stratospheric and mesospheric sounder and microwave limb sounder temperature fields at Kelvin wave scales

Space-time analyses, which are sensitive to details of retrieval and gridding processes not seen in zonal and time means, are used to investigate the integrity of version 8 gridded retrieved temperatures from the improved stratospheric and mesospheric sounder (ISAMS) on the upper atmosphere research satellite (UARS). This note presents results of such analyses applied to ISAMS tropical data. Comparisons are made with microwave limb sounder (MLS), also on UARS, temperatures. Prominent zonal wave number 1 features are observed with characteristics similar to those expected for Kelvin waves. Time versus longitude plots reveal quasi-regular eastward phase progression from November 1991 to mid-January 1992. The perturbations extend throughout the upper stratosphere and lower mesosphere (altitudes of 32-64 km), exhibiting peak-to-peak amplitudes of up to 2°-3° K and periods from ∼2 weeks in midstratosphere to ∼1 week at higher altitudes. Faster Kelvin waves with periods of 3-5 days are also found in the lower mesosphere. Height versus time plots reveal downward phase and upward group velocities, consistent with forcing from below. Vertical wavelengths are ∼20 km for the slower mode and about twice this scale for the faster 3 to 5-day mode. The features are trapped within ±10°-15° of the equator. Kelvin wave signatures in ISAMS and MLS temperatures are compared at 10 and 1 hPa. Good agreement is found, illustrating the internal consistency and ability of both ISAMS and MLS temperature grids to capture relatively small amplitude features with space-time scales of fast, zonally asymmetric equatorial modes.

Rossby‐gravity waves in tropical total ozone

Randel (1992) has recently reported evidence for Rossby-gravity waves in tropical data fields produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The purpose of this paper is to show that similar features are observable in fields of total column ozone from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The observed features are episodic, have zonal (east-west) wavelengths of approximately 6,000-10,000 km and oscillate with periods of 5-10 days. The modes exhibit westward phase progression and eastward group velocity. A simple linear model is used to estimate the magnitude of total ozone perturbations induced by Rossby-gravity waves. The model is able to account for the magnitude of observed TOMS features as well as their asymmetry about the equator. The significance of finding Rossby-gravity waves in total ozone fields is that: (1) the report of similar features in ECMWF tropical fields is corroborated with an independent data set; and (2) the TOMS data set is demonstrated to possess surprising versatility and sensitivity to relatively smaller scale tropical phenomena.

CH4 and N2O photochemical lifetimes in the upper stratosphere - In situ estimates using SAMS data

Upper stratospheric photochemical lifetimes are estimated in situ for CH{sub 4} and N{sub 2}O for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high Northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N{sub 2}O at 2 and 7 hPa ({approximately} 43 and {approximately}35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CH{sub 4}, 0.6 ({approximately} 52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et al. (1986).