Handbook of optics

Localized fluid flow measurements with an He-Ne laser spectrometer

[1] We have used the Whole Atmosphere Community Climate Model to produce a small (three-member) ensemble of simulations of the period 1950–2003. Comparison of model results against available observations shows that for the most part, the model is able to reproduce well the observed trends in zonal mean temperature and ozone, both as regards their magnitude and their distribution in latitude and altitude. Calculated trends in water vapor, on the other hand, are not at all consistent with observations from either the HALOE satellite instrument or the Boulder, Colorado, hygrosonde data set. We show that such lack of agreement is actually to be expected because water vapor has various sources of low-frequency variability (heating due to volcanic eruptions, the quasi-biennial oscillation and El Nino–Southern Oscillation) that can confound the determination of secular trends. The simulations also reveal the presence of other interesting behavior, such as the lack of any significant temperature trend near the mesopause, a decrease in the stratospheric age of air, and the rare occurrence of an extremely disturbed Southern Hemisphere winter.

/pdf/simulation-of-secular-trends-in-the-middle-atmosphere-1950-529l1votox.pdf

Simulation of secular trends in the middle atmosphere, 1950–2003

Rayleigh scattering is a powerful diagnostic tool for the study of gases and is particularly useful for aiding in the understanding of complex flow fields and combustion phenomena. Although the mechanism associated with the scattering, induced electric dipole radiation, is conceptually straightforward, the features of the scattering are complex because of the anisotropy of molecules, collective scattering from many molecules and inelastic scattering associated with rotational and vibrational transitions. These effects cause the scattered signal to be depolarized and to have spectral features that reflect the pressure, temperature and internal energy states of the gas. The very small scattering cross section makes molecular Rayleigh scattering particularly susceptible to background interference. Scattering from very small particles also falls into the Rayleigh range and may dominate the scattering from molecules if the particle density is high. This particle scattering can be used to enhance flow visualization and velocity measurements, or it may be removed by spectral filtering. New approaches to spectral filtering are now being applied to both Rayleigh molecular scattering and Rayleigh particle scattering to extract quantitative information about complex gas flow fields. This paper outlines the classical properties of Rayleigh scattering and reviews some of the new advances in flow field imaging that have been achieved using the new filter approaches.

https://iopscience.iop.org/article/10.1088/0957-0233/12/5/201/pdf

Laser Rayleigh scattering

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

Over the past decade, we have seen extensive research on and application with Raman gain and other types of coherent Raman spectroscopies. These activities have made clear the advantages of coherent spectroscopy:high signal-to-noise, excellent discrimination from stray light and fluorescence backgrounds, and high spectral resolution. While Raman spectroscopy probes frequency shifts typically 10 cm−1 to 3000 cm−1 from the exciting laser line, information on thermal properties of the medium, which include thermal conductivity, shear and bulk viscosities, and lower-frequency excitations may be obtained from quasi-elastic Rayleigh-Brillouin scattering.

Rayleigh-Brillouin Gain Spectroscopy in Gases

A novel narrowband lidar, probing the fluorescence of atmospheric Na atoms was deployed in Fort Collins, CO. We discuss the novelty of our lidar system, followed by a number of interesting and important atmospheric phenomena.

The CSU sodium lidar facility: Current observation capability and science

Tidal influence in the determination of long-term trends in the mesosphere-lower thermosphere from LIDAR observations

Using stimulated Rayleigh-Brillouin-gain spectroscopy, velocity measurements in an atmospheric-pressure subsonic nitrogen flow with 10 percent uncertainty have been conducted. It is shown that the accuracy of the velocity measurements increases with gas pressure, making this spectroscopic technique ideal for measuring velocity and other parameters of high-pressure (greater than 1-atm) atomic or molecular flows.

Chiao-Yao She

Papers

Rayleigh-Brillouin Gain Spectroscopy in Gases

The CSU sodium lidar facility: Current observation capability and science

Tidal influence in the determination of long-term trends in the mesosphere-lower thermosphere from LIDAR observations

Flow-velocity measurements with stimulated Rayleigh-Brillouin gain spectroscopy

Spatially resolved two-component flow-velocity measurements with inverse Raman spectroscopy