Aspects of Middle Atmosphere Dynamics and Ozone

Current research in our group is focused on several aspects of satellite observations and dynamics of ozone and the middle atmosphere.

1. UPPER ATMOSPHERE RESEARCH SATELLITE

UARS data are being utilized to analyze and interpret the structure and circulation patterns in the stratosphere and mesosphere. There are three aspects of this work:

1. Four-day Wave in Polar Winter Stratosphere and Mesosphere

   The "4-day wave", a unique feature discovered a decade and a half ago (Venne and Stanford, J. Atmos. Sci. 1979, 1982), exists only in the polar winter night stratosphere and consists of perturbations in temperature and constituents (such as ozone) which revolve around the pole with about a four-day period. Theoretical predictions suggest it is a barotropic and/or baroclinic instability, drawing energy from wind gradients in the strong polar night stratospheric jet stream.

   A combined observational and theoretical modeling paper has been published by Allen et al. (1997), The 4-Day Wave as Observed from the Upper Atmosphere Research Satellite Microwave Limb Sounder. Observations from the UARS Microwave Limb Sounder instrument, which are considerably improved over earlier data, were used.

   A review of observational and theoretical investigations of the 4-day wave can be found in The 4-Day Wave, Stanford (1999).

2. Middle atmosphere circulation deduced from ISAMS carbon monoxide (CO) data.

   CO is a constituent whose mixing ratio, in distinction to most other trace gases, increases with altitude. This unique property is utilized to investigate the circulation of the upper stratosphere and mesosphere.

   We are investigating seasonal scale and shorter motions in the upper stratosphere and lower mesosphere by analyzing observations of carbon monoxide (CO) from the Improved Stratospheric and Mesospheric Sounder (ISAMS) instrument flown on the Upper Atmosphere Research Satellite (UARS).

   The first part of our study dealt with the dynamically active early northern winter 1991/1992. The results are presented in Allen et al. (1999), Observations of middle atmosphere CO from the UARS ISAMS during the early northern winter 1991/1992.

   We have also investigated the less well studied Southern winter upper stratosphere and lower mesosphere, using ISAMS CO data from two months in the austral autumn and early winter. The results are presented in Allen et al., (2000), Antarctic polar descent and planetary wave activity observed in ISAMS CO from April to July 1992. This work involves colleagues in the Instituto de Astrofisica de Andalucia, Granada, Spain, University of Chicago - Department of Geophysical Sciences, Goddard Space Flight Center - Atmospheric Chemistry and Dynamics Branch, and University of Oxford - Department of Atmospheric, Oceanic and Planetary Physics).

3. Upper Tropospheric Water Vapor Analyses

   In conjunction with colleagues at NASA-Jet Propulsion Laboratory we are investigating upper tropospheric WV measurements from the UARS Microwave Limb Sounder instrument. Stone, et al. (1996) found clear signals of baroclinic wave structures in the upper troposphere water vapor data of MLS and results are presented in ( Baroclinic Wave Variations Observed in MLS Upper Tropospheric Water Vapor). More detailed studies of along-track data are in progress. See also under Item 3 below.

2. OZONE INVESTIGATIONS

We are involved with analyses of total column ozone measurements made by NASA's Total Ozone Mapping Spectrometer (TOMS). Recently we've been investigating global ozone data sets by space-time spectral analysis techniques. A number of intriguing features were discovered in the data:

• The first evidence for Rossby-gravity waves in any atmospheric constituent data (Stanford & Ziemke,Geophys. Res. Lett.,(1993)). Their discovery in ozone data was a surprise. These unique equatorial waves are excited in the lower (troposphere) layer of the atmosphere and propagate upwards where, due to their absorption into the background flow, they are thought to be important in forcing large-scale stratospheric circulation.

• We have also found evidence for several other atmospheric wave modes in the total ozone fields, including Kelvin waves ( Ziemke & Stanford, Geophys. Res. Letts. (1994a)), and have shown that these waves exhibit a unique dynamical relationship with the important quasi-biennial wind oscillation in the stratosphere ( Ziemke & Stanford, J. Geophys. Res. (1994b)).
  The significance of finding such features in total ozone fields is:
  1. The TOMS data set is demonstrated to possess surprising versatility and sensitivity to tropical phenomena.
  2. TOMS data can be used to validate models in the relative data-poor low latitudes.

  We have completed a NASA Reference document (80 pages) giving details of TOMS total ozone space-time spectral analyses (Stanford, et al., NASA Ref. Publ. No. 1360(1995)). A second NASA Reference document (32 pages) gives details of comparisons between TOMS Version 6 and Version 7 Total Ozone fields, examined with space-time spectral analyses (Olsen, et al., NASA Ref. Publ. No. 1490(1997). For other recent ozone papers, see Publications.

  The M.S. thesis work of Michael Lewis used similar space-time spectral analysis techniques for investigations of ozone data from the Solar Backscatter Ultra Violet (SBUV) instrument data from Goddard Space Flight Center.

  Small-Scale Tropopause Dynamics and TOMS Total Ozone:

• Ph. D. student Mark Olsen is using Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) along-track ozone retrievals, in conjunction with ancillary meteorological fields and modeling studies, for high resolution investigations of upper troposphere and lower stratosphere dynamics. Specifically, high-resolution (25-50 km) along-track EP TOMS data are being used to investigate the beautiful fine-scale structure in constituent and meteorological fields prominent in the evolution of highly non-linear baroclinic storm systems. Comparisons are made with high resolution (40 km) models of the National Centers for Environmental Prediction (NCEP), contour advection modeling by University of Oxford colleagues using the UK Universities' Global Atmospheric Modelling Programme (UGAMP), and the Goddard Space Flight Center Chemistry Transport Model (CTM). A spin off of the work is investigation of the relationship between total ozone and the tropospheric jet field, of application to aircraft routing. The analyses also provide internal consistency checks and validation of the EP TOMS data which are vital for monitoring ozone depletion in both polar and midlatitude regions.

  Preliminary analyses of EP TOMS along-track ozone data are revealing excellent agreement with very fine scale features (100 km and under) in upper tropospheric/lower stratospheric dynamical fields predicted by the NOAA/FSL Rapid Update Cycle model developed by colleagues at NOAA/FSL in Boulder, Colorado. We also are collaborating in these fine-scale, near-tropopause dynamical studies with Professor William Gallus and Graduate Student Melissa Horton in the ISU Department of Geological and Atmospheric Sciences.

  Initial results reveal good correspondence between fine-scale details in TOMS total ozone and mesoscale model output. The three-dimensional mesoscale model output aids in interpretation of the TOMS data in terms of tropopause structure and evolution induced by baroclinic dynamics in the upper troposphere and lower stratosphere. The results are discussed in Olsen, et al. (2000): Fine-scale comparison of TOMS total ozone data and model analysis of an intense Midwestern cyclone .

3. TROPOSPHERIC CONSTITUENT VARIABILITY ASSOCIATED WITH BAROCLINIC WAVES

• ISU Ph.D.Elizabeth Stone conducted her research at the National Center for Atmospheric Research, Boulder, Colorado. The focus of her work involves understanding atmospheric constituent transport associated with baroclinic waves. Baroclinic waves are a prominent dynamical feature in the circulation patterns of the extratropical troposphere (below about 15 km). They are medium scale waves (4-7 wavelengths fit around a latitude circle) that arise from instability in the zonal circulation. The waves often exhibit clearly defined life cycles of baroclinic growth, maturity and barotropic decay. They also provide the major means of meridional heat and momentum transport in the lower atmosphere. This work involves understanding and detailing atmospheric constituent transport associated with these wave events utilizing satellite measurements and model simulations.

• In a case study which examined upper tropospheric water vapor measurements from the Microwave Limb Sounder instrument on board the Upper Atmosphere Research Satellite, we investigated the structure and evolution of eastward traveling medium scale wave features in the water vapor data and the corresponding meteorological fields. The results were consistent with paradigms for the structure and evolution of baroclinic disturbances. The paper, Baroclinic wave variations observed in MLS upper tropospheric water vapor , by Stone et al., is published in Geophysical Research Letters (1996).

• This project utilized the three dimensional NCAR Community Climate Model (CCM2) to simulate idealized baroclinic wave life cycles. The model was initialized with two different baroclinically unstable states and four idealized passive tracers which were advected by the CCM2 semi-Lagrangian transport scheme. The different constituent distributions were used to assess the influence of the initial distribution on transport characteristics. The model output displays life cycles of wave growth and decay with distinctive non-linear development for the two cases. The evolutions of the tracers were investigated throughout the model simulations and their budgets analyzed in terms of the transformed Eulerian mean constituent transport formalism. The results are reported in Stone, et al. (1999): Transport of Passive Tracers in Baroclinic Wave Life Cycles.

  These studies involve collaboration with Dr. William Randel at the National Center for Atmospheric Research, Boulder, Colorado..

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