The quasi-biennial oscillation (QBO) dominates the variability of the equatorial stratosphere (∼16–50 km) and is easily seen as downward propagating easterly and westerly wind regimes, with a variable period averaging approximately 28 months. From a fluid dynamical perspective, the QBO is a fascinating example of a coherent, oscillating mean flow that is driven by propagating waves with periods unrelated to that of the resulting oscillation. Although the QBO is a tropical phenomenon, it affects the stratospheric flow from pole to pole by modulating the effects of extratropical waves. Indeed, study of the QBO is inseparable from the study of atmospheric wave motions that drive it and are modulated by it. The QBO affects variability in the mesosphere near 85 km by selectively filtering waves that propagate upward through the equatorial stratosphere, and may also affect the strength of Atlantic hurricanes. The effects of the QBO are not confined to atmospheric dynamics. Chemical constituents, such as ozone, water vapor, and methane, are affected by circulation changes induced by the QBO. There are also substantial QBO signals in many of the shorter-lived chemical constituents. Through modulation of extratropical wave propagation, the QBO has an effect on the breakdown of the wintertime stratospheric polar vortices and the severity of high-latitude ozone depletion. The polar vortex in the stratosphere affects surface weather patterns, providing a mechanism for the QBO to have an effect at the Earth's surface. As more data sources (e.g., wind and temperature measurements from both ground-based systems and satellites) become available, the effects of the QBO can be more precisely assessed. This review covers the current state of knowledge of the tropical QBO, its extratropical dynamical effects, chemical constituent transport, and effects of the QBO in the troposphere (∼0–16 km) and mesosphere (∼50–100 km). It is intended to provide a broad overview of the QBO and its effects to researchers outside the field, as well as a source of information and references for specialists. The history of research on the QBO is discussed only briefly, and the reader is referred to several historical review papers. The basic theory of the QBO is summarized, and tutorial references are provided.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999RG000073

The quasi-biennial oscillation

[1] The global-scale wave model (GSWM) is used to investigate mesospheric and lower thermospheric migrating and nonmigrating diurnal tidal components that propagate upward from the troposphere, where they are excited by latent heat release associated with deep tropical convection. Our diurnal tidal forcing parameterization is derived from a 7-year database of global cloud imagery. The GSWM migrating response is sufficiently large to modulate the dominant radiatively excited migrating diurnal tide in the middle and upper atmosphere during every month of the year. Five additional nonmigrating diurnal components, the eastward propagating zonal wave numbers 2 and 3, the westward propagating zonal wave number 2, and the standing oscillations, also introduce significant longitudinal variability of the diurnal tide in these regions. The comparative importance of the nonmigrating components evolves from month to month and varies with tidal field. Our GSWM investigation suggests that other dynamical models must account for the tropospheric latent heat source in order to make realistic predictions of the diurnal tide in the middle and upper atmosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JD001236

Migrating and nonmigrating diurnal tides in the middle and upper atmosphere excited by tropospheric latent heat release

Preface 1. Basic properties of radiation, atmospheres and oceans 2. Basic state variables 3. Interaction of radiation with matter 4. Formulation of radiative transfer problems 5. Approximate solutions of prototype problems 6. Accurate numerical solutions of prototype problems 7. Emission-dominated radiative processes 8. Radiative transfer in spectrally-complex media 9. Solar radiation driving photochemistry and photobiology 10. The role of radiation in climate Appendix 1. A primer on radiative transfer: absorption and scattering opacity Appendix 2. Stokes parameters, Poincare sphere, and the Mueller matrix Appendix 3. Nomenclature: glossary of symbols Appendix 4. Principle of reciprocity for the bidirectional reflectance Appendix 5. Isolation of the azimuth-dependence Appendix 6. The streaming term in spherical geometry Appendix 7. Reflectance and transmittance of the invariant intensity (I n2) Appendix 8. Scaling transformation for anisotropic scattering Appendix 9. Reciprocity, duality and effects of surface reflection Appendix 10. Removal of overflow problems in the intensity formulas.

Radiative Transfer in the Atmosphere and Ocean

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1333301

The Horizontal Wind Model (HWM) has been updated in the thermosphere with new observations and formulation changes. These new data are ground-based 630 nm Fabry-Perot Interferometer (FPI) measurements in the equatorial and polar regions, as well as cross-track winds from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite. The GOCE wind observations provide valuable wind data in the twilight regions. The ground-based FPI measurements fill latitudinal data gaps in the prior observational database. Construction of this reference model also provides the opportunity to compare these new measurements. The resulting update (HWM14) provides an improved time-dependent, observationally based, global empirical specification of the upper atmospheric general circulation patterns and migrating tides. In basic agreement with existing accepted theoretical knowledge of the thermosphere general circulation, additional calculations indicate that the empirical wind specifications are self-consistent with climatological ionosphere plasma distribution and electric field patterns.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014EA000089

An update to the Horizontal Wind Model (HWM): The quiet time thermosphere

The Space Physics Research Laboratory at the University of Michigan has been operating a direct detection, high resolution Doppler Lidar (HRDL) to measure winds in the boundary layer, free troposphere and lower stratosphere. A direct detection Doppler lidar measures the Doppler shift of the aerosol or Rayleigh backscattered signal, from which the wind velocity vector can be retrieved (Benedetti-Michelangeli et al, 1972, 1974; Chanin et al., 1989; Abreu et al., 1992). The system components are shown. The transmitting system is a Continuum NY-60 Nd:YAG laser frequency doubled to a wavelength of 532 nm. The laser is injection seeded for single line mode operation yielding a linewidth of 0.0045 cm(exp -1) (135 MHz) with excellent shot-to-shot frequency stability. The laser produces 60 mJ pulses and operates at a 50 Hz repetition rate for an effective output power of 3.0 W. A description of the University of Michigan's Doppler lidar is given with examples of wind profiles for the boundary layer, free troposphere, and for the lower stratosphere. The system provides a reliable method of remotely measuring the wind. The wind error is smallest in regions of high aerosols. The system also produces aerosol extinction profiles versus altitude which can be determined by the shape of the spectra. The system has been installed in a trailor so that measurements can be made for field campaigns. Winds and aerosol data are available immediately at the site for use in forecasting.

Tropospheric and stratospheric wind profiling with a direct detection Doppler lidar

Monitoring tropospheric chemistry from space is the next frontier for advancing present-day remote sensing capabilities to meet future high-priority atmospheric science measurement needs. The Tropospheric Trace Species Sensing Fabry-Perot Interferometer (TTSS-FPI) is a NASA Instrument Incubator Program (IIP) project for risk mitigation of enabling concepts and technology applicable to future Office of Earth Science (OES) atmospheric chemistry measurements. While the intended implementation for future science missions is a geostationary based measurement of tropospheric ozone and other trace species, a multispectral imaging airborne sensor system is being developed within IIP to demonstrate the instrument concept and enabling technologies that are also applicable to space-based configurations. The concept is centered about an imaging Fabry-Perot interferometer (FPI) observing a narrow spectral interval within the strong 9.6 micron ozone infrared band with a spectral resolution ~ 0.07 cm-1. This concept is also applicable to and could simplify designs associated with atmospheric chemistry sensors targeting other trace species (which typically require spectral resolutions in the range of 0.01 - 0.1 cm-1), since such an FPI approach could be implemented for those spectral bands requiring the highest spectral resolution and thus simplify overall design complexity. An overview of this IIP project addressing the measurement and instrument concepts, enabling technologies, approach for development and demonstration, and a summary of progress-to-date will all be reported. This will include sensor radiometric, spectral, and spatial characterization activities relevant to measurement concept validation. Subsequent manuscripts following in these proceedings will focus on the airborne prototype system under development and a corresponding spaceflight concept study, respectively.

Tropospheric Trace Species Sensing FPI: program overview and measurement concept validation

Horizontal winds in the mesosphere and lower thermosphere are obtained with the high resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) by observing the Doppler shifts of emission lines in the O 2 atmospheric band. The validity of the measurements depends on an accurate knowledge of the positions on the detector of the observed lines in the absence of a wind induced Doppler shift. These positions have been determined to an accuracy of better than 5 ms -1 from the comparison of winds measured by HRDI with those obtained by MF radars and rockets. In addition, the degrees of horizontal and vertical smoothing of the recovered wind profiles have been optimized by examining the effect both on the amplitude of the HRDI derived diurnal tidal amplitude and the variance of the wind differences with correlative data.

Validation of winds from the High-Resolution Doppler Imager on the Upper Atmosphere Research Satellite (UARS)

https://www.osapublishing.org/viewmedia.cfm?URI=CLEO-1993-CMC4

High resolution Doppler imager on UARS

The Upper Atmosphere Research Satellite (UARS), to be launched in 1989, is to provide a global data set required to understand the mechanisms controlling upper atmosphere structure and processes, as well as the response of the upper atmosphere to natural and human perturbations. The High Resolution Doppler Imager (HRDI) is the primary instrument for measuring the dynamics of the stratosphere and mesosphere. The goal of HRDI is to measure wind velocities in the stratosphere and mesosphere during the day and the mesosphere and thermosphere at night with an accuracy of 5 m/sec. HRDI will determine winds by measuring Doppler shifts of atmosphere absorption and emission features. Line of sight winds will be taken in two directions, thus allowing the wind vector to be formed. The HRDI instrument is overviewed. The basis of the measurement is explained, as is an outline of the instrument. Since neither instrument nor observational techniques is fully mature, only a brief sketch is presented.

Wilbert R. Skinner

Papers

Tropospheric and stratospheric wind profiling with a direct detection Doppler lidar

Tropospheric Trace Species Sensing FPI: program overview and measurement concept validation

Validation of winds from the High-Resolution Doppler Imager on the Upper Atmosphere Research Satellite (UARS)

High resolution Doppler imager on UARS

Wind measurements with the High Resolution Doppler Imager (HRDI)