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 High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite has been providing measurements of the wind field in the stratosphere, mesosphere, and lower thermosphere since November 1991 Mesospheric temperatures, ozone and O( 1 D) densities, and stratospheric aerosol extinctions coefficients, are also retrieved The instrument characteristics have been carefully monitored by frequent calibrations during the nearly eight years of operation The instrument sensitivity showed a significant decrease (close to 50% in some cases) during the first seven and a half years of operation which was caused by the piezoelectric-controlled etalons slowly drifting from a parallel state A recalibration of the etalons in late 1998 resulted in close to a complete recovery of the instrument sensitivity The loss of sensitivity was linear with time, with discrete changes occurring at times Careful modeling of the data permits a determination of the sensitivity as a function of time, allowing the data to be corrected for this systematic effect

High-resolution Doppler imager: instrument performance from late 1991 to mid-1999

Data from the Fabry-Perot interferometer on board the Dynamics Explorer-B satellite is used to show that the contaminant glow observed by Yee and Abreu at 7320A on the AE satellites is produced by emission lines of one or more species. A comparison is made of the contaminant spectrum near 7320A with the nightglow OH spectrum measured below 155km. Evidence is presented to the effect that OH might be one of the metastable species producing the glow.

/pdf/optical-effects-of-spacecraft-environment-interaction-16l4r8177e.pdf

Optical effects of spacecraft-environment interaction Spectrometric observations by the DE-B satellite

The high resolution doppler imager (HRDI) on the upper atmosphere research satellite has been providing measurements of the wind field in the stratosphere, mesosphere and lower thermosphere since November 1991. Mesospheric temperatures, ozone and O( 1 D), as well as stratospheric aerosol extinctions, are also recovered. The instrument characteristics have been carefully monitored during the nearly five years of operation. The instrument thermal and long-term drifts can be removed from the data, and wind biases are less than about 2 m/s. The interferometer sensitivity has varied by about 3 percent, most likely due to changes in the parallelism of one of the etalons. There is not indication that either the radiator or thermal blankets have shown any significant degradation. Recently, the azimuth slew rate of the telescope has displayed some variation, which may indicate an increase of bearing friction.

High-Resolution Doppler Imager: instrument performance in orbit since late 1991

Doppler lidars can be separated into two main categories by the detection technique used, coherent or incoherent. This paper focuses on the differences between the two types of Doppler lidar and the effect of speckle on each. Coherent Doppler lidars make use of a local oscillator heterodyning system similar in principle to a Doppler radar to determine Doppler shift while incoherent lidars typically use an interferometric technique to resolve the small spectral shift. The effect of laser speckle on lidar measurements in general has become a topic of great interest in recent years because in many cases it limits the ultimate resolution or accuracy of the measurement. In the case of Doppler lidars, speckle has very different effects on coherent and incoherent Doppler detection systems. Due to the single-shot nature of coherent lidar measurements and the narrow field of view required, many shots of data are lost due to speckle. The larger fields of view used for incoherent Doppler lidar as well as the inherent multiple pulse averaging make speckle significantly less of a problem for these systems.

Effect of speckle on coherent and incoherent Doppler lidar

The High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) has been measuring winds in the stratosphere, mesosphere and lower thermosphere since November, 1991. The winds are determined by measuring the Doppler shift of emission and absorption lines in the O2 Atmospheric Band that are located between 630 and 762 nm. HRDI is a triple-etalon Fabry-Perot interferometer that has a resolution of ~0.05 cm-1 and very good white light rejection. A multi-channel detector with 31 channels is used to examine a spectral region 0.5 cm-1 wide and an adjustable filter wheel permits the selection of any one of 13 spectral bands. The long life of this instrument has presented many challenges in keeping the calibrations current and in compensating for inevitable degradations in instrument and spacecraft performance. Some of the problems with the UARS spacecraft the affect HRDI operations are: limited power due to the solar array drive failure; loss of data resulting from a failure of the tape recorders, and loss of attitude knowledge caused by the failure of the star trackers. HRDI has shown little loss in capability over the years
with only a decrease in the azimuth rate of the telescope motor a significant sign of aging. This paper will discuss some of these challenges and how they have been met.

Wilbert R. Skinner

Papers

High-resolution Doppler imager: instrument performance from late 1991 to mid-1999

Optical effects of spacecraft-environment interaction Spectrometric observations by the DE-B satellite

High-Resolution Doppler Imager: instrument performance in orbit since late 1991

Effect of speckle on coherent and incoherent Doppler lidar

The High-Resolution Doppler Imager: status update 12 years after launch