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

Seasonal and local time variations in the O(1S) green line, O2 atmospheric band, and OH Meinel band emissions as measured by the High Resolution Doppler Imager

Comparisons are made between climatological dynamic fields obtained from ground-based (GB) and space- based (SB) instruments with a view towards identifying SB/GB intercalibration issues for TIMED and other future aeronomy satellite missions. SB measurements are made from the High Resolution Doppler Imager (HRDI) instru- ment on the Upper Atmosphere Research Satellite (UARS). The GB data originate from meteor radars at Obninsk, (55 N, 37 E), Shigaraki (35 N, 136 E) and Jakarta (6 S, 107 E) and MF spaced-antenna radars at Hawaii (22 N, 160 W), Christmas I. (2 N, 158 W) and Adelaide (35 S, 138 E). We focus on monthly-mean prevailing, diurnal and semidiurnal wind components at 96 km, averaged over the 1991-1999 period. We perform space-based (SB) analyses for 90 longitude sectors including the GB sites, as well as for the zonal mean. Taking the monthly prevailing zonal winds from these stations as a whole, on average, SB zonal winds exceed GB determinations by 63%, whereas merid- ional winds are in much better agreement. The origin of this discrepancy remains unknown, and should receive high pri- ority in initial GB/SB comparisons during the TIMED mis- sion. We perform detailed comparisons between monthly clima- tologies from Jakarta and the geographically conjugate sites of Shigaraki and Adelaide, including some analyses of in- terannual variations. SB prevailing, diurnal and semidiur- nal tides exceed those measured over Jakarta by factors, on the average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind, although much variability exists. For the meridional component, SB/GB ratios for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and tidal amplitudes at Adelaide are significantly lower than SB val- ues, whereas similar net differences do not occur at the con- jugate Northern Hemisphere location of Shigaraki. Adelaide diurnal phases lag SB phases by several hours, but excellent agreement between the two data sources exists for semidiur- nal tidal phases throughout the year. These results are con- sistent with phase retardation effects in the MF radar tech- nique that are thought to exist above about 90 km. Prevail- ing and tidal amplitudes from Shigaraki track year-to-year variations in SB fields, whereas in the Southern Hemisphere poorer agreement exists. The above hemispheric differences are due in part to MF vs. meteor radar techniques, but zonal asymmetries and day-to-day variability, combined with inad- equate sampling, may also be playing a role. Based on these results, some obvious recommendations emerge that are rele- vant to combined GB/SB studies as part of TIMED and other future aeronomy missions.

/pdf/climatological-lower-thermosphere-winds-as-seen-by-ground-3zb53lpc5x.pdf

Climatological lower thermosphere winds as seen by ground-based and space-based instruments

A method is described for determining the angular misalignment between the High Resolution Doppler Imager instrument and its spacecraft, the Upper Atmospheric Research Satellite, using observations of stars by the instrument. Roll, pitch, and yaw misalignments have been measured to within 0.0025 deg (l<r), which is an order of magnitude better than the largest tolerable alignment error. The misalignment results are validated using observations of the nighttime 5577-A O^S) green line emission. In addition, the long-term behavior of the derived alignment offsets, which shows a clear dependence of the alignment on the solar (3 angle, is presented. Nomenclature px = vector in the instrument's viewing direction expressed in the x coordinate frame Tx/y = transformation matrix from the y to the x coordinate frame t = measured time of the star crossing, s to = calculated star crossing time for the known star position and spacecraft position and attitude, s rjo = known angular misalignment vector, deg ?7i = angular misalignment between the instrument and spacecraft frame about the roll axis of the spacecraft, deg 772 = angular misalignment between the instrument and spacecraft frame about the pitch axis of the spacecraft, deg 773 = angular misalignment between the instrument and spacecraft frame about the yaw axis of the spacecraft, deg 3rj/31 = derivative of the misalignment with respect to crossing time expressed as a three-element column vector (in roll, pitch, and yaw), deg/s

/pdf/stellar-alignment-of-the-high-resolution-doppler-imager-1ksaljxm3s.pdf

Stellar Alignment of the High Resolution Doppler Imager

A Comparative Study of Coherent & Incoherent Doppler Lidar Techniques

Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud layers into a multiple-scattering radiative transfer model. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979-1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1-1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud layer method and a multiple cloud layer method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud layers may be important in accurately determining the biologically effective UV budget at the surface of the Earth.

Wilbert R. Skinner

Papers

Seasonal and local time variations in the O(1S) green line, O2 atmospheric band, and OH Meinel band emissions as measured by the High Resolution Doppler Imager

Climatological lower thermosphere winds as seen by ground-based and space-based instruments

Stellar Alignment of the High Resolution Doppler Imager

A Comparative Study of Coherent & Incoherent Doppler Lidar Techniques

Incorporation of multiple cloud layers for ultraviolet radiation modeling studies