Chiao-Yao She

Review of mesospheric temperature trends

In recent times it has become increasingly clear that releases of trace gases from human activity have a potential for causing change in the upper atmosphere. However, our knowledge of systematic changes and trends in the temperature of the mesosphere and lower thermosphere is relatively limited compared to the Earths lower atmosphere, and not much effort has been made to synthesize these results so far. In this article, a comprehensive review of long-term trends in the temperature of the region from 50 to 100 km is made on the basis of the available up-to-date understanding of measurements and model calculations. An objective evaluation of the available data sets is attempted, and important uncertainly factors are discussed. Some natural variability factors, which are likely to play a role in modulating temperature trends, are also briefly touched upon. There are a growing number of experimental results centered on, or consistent with, zero temperature trend in the mesopause region (80–100 km). The most reliable data sets show no significant trend but an uncertainty of at least 2 K/decade. On the other hand, a majority of studies indicate negative trends in the lower and middle mesosphere with an amplitude of a few degrees (2–3 K) per decade. In tropical latitudes the cooling trend increases in the upper mesosphere. The most recent general circulation models indicate increased cooling closer to both poles in the middle mesosphere and a decrease in cooling toward the summer pole in the upper mesosphere. Quantitatively, the simulated cooling trend in the middle mesosphere produced only by CO 2 increase is usually below the observed level. However, including other greenhouse gases and taking into account a “thermal shrinking” of the upper atmosphere result in a cooling of a few degrees per decade. This is close to the lower limit of the observed nonzero trends. In the mesopause region, recent model simulations produce trends, usually below 1 K/decade, that appear to be consistent with most observations in this region

High spectral resolution lidar system with atomic blocking filters for measuring atmospheric parameters

A new lidar technique for measuring the profiles of backscatter ratio, atmospheric visibility, and atmospheric temperature is proposed. Based on the theory of high resolution Rayleigh/Mie scattering, the feasibility and advantages of using atomic vapor cells as blocking filters for measuring atmospheric parameters are demonstrated with a numerical example worked out in detail. Ten percent accuracy in determining backscatter ratio and visibility can be achieved easily. With a SNR of 300, temperature of 1 K accuracy can be measured directly along with the backscatter ratio to a better accuracy of ±1%. Using a large lidar system and assuming 50-km visibility, the proposed technique can be applied to measure backscatter ratio and temperature profiles simultaneously for a 10-km path with 30-m depth resolution in 3 min. With higher SNR the atmospheric pressure profile can also be determined.

Climatology of mesopause region temperature, zonal wind, and meridional wind over Fort Collins,Colorado (41°N, 105°W), and comparison with model simulations

[1] Between May 2002 and April 2006, many continuous observations of mesopause region temperature and horizontal wind, each lasting longer than 24 h (termed full-diurnal-cycle observations), were completed at the Colorado State University Na Lidar Facility in Fort Collins, Colorado (41°N, 105°W). The combined data set consists of 120 full-diurnal-cycle observations binned on a monthly basis, with a minimum of 7 cycles in April and a maximum of 18 cycles in August. Each monthly data set was analyzed to deduce mean values and tidal period perturbations. After removal of tidal signals, monthly mean values are used for the study of seasonal variations in mesopause region temperature, zonal and meridional winds. The results are in qualitative agreement with our current understanding of mean temperature and wind structures in the midlatitude mesopause region with an observed summer mesopause of 167 K at 84 km, summer peak eastward zonal wind of 48 m/s at 94 km, winter zonal wind reversal at ∼95 km, and peak summer (pole) to winter (pole) meridional flow of 17 m/s at 86 km. The observed mean state in temperature, zonal and meridional winds are compared with the predictions of three current general circulation models, i.e., the Whole Atmosphere Community Climate Model version 3 (WACCM3) with two different simulations of gravity wavefields, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), and the 2003 simulation of the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). While general agreement is found between observation and model predictions, there exist discrepancies between model prediction and observation, as well as among predictions from different models. Specifically, the predicted summer mesopause altitude is lower by 3 km, 8 km, 3 km, and 1 km for WACCM3 the two WACCM runs, HAMMONIA, and TIME-GCM, respectively, and the corresponding temperatures are 169 K, 170 K, 158 K, and 161 K. The model predicted summer eastward zonal wind peaks to 71 m/s at 102 km, to 48 m/s at 84 km, to 75 m/s at 93 km, and to 29 m/s at 94 km, in the same order. The altitude of the winter zonal wind reversal and seasonal asymmetry of the pole-to-pole meridional flow are also compared, and the importance of full-diurnal-cycle observations for the determination of mean states is discussed.

High-spectral-resolution lidar with iodine-vapor filters: measurement of atmospheric-state and aerosol profiles.

A high-spectral-resolution lidar can measure vertical profiles of atmospheric temperature, pressure, the aerosol backscatter ratio, and the aerosol extinction coefficient simultaneously. We describe a system with these characteristics. The transmitter is a narrow-band (FWHM of the order of 74 MHz), injection-seeded, pulsed, double YAG laser at 532 nm. Iodine-vapor filters in the detection system spectrally separate the molecular and aerosol scattering and greatly reduce the latter (-41 dB). Operating at a selected frequency to take advantage of two neighboring lines in vapor filters, one can obtain a sensitivity of the measured signal-to-air temperature ratio equal to 0.42%/K. Using a relatively modest size transmitter and receiver system (laser power times telescope aperture equals 0.19 Wm(2)), our measured temperature profiles (0.5-15 km) over 11 nights are in agreement with balloon soundings to within 2.0 K over an altitude range of 2-5 km. There is good agreement in the lapse rates, tropopause altitudes, and inversions. In principle, to invert the signal requires a known density at one altitude, but in practice it is convenient to also use a known temperature at that altitude. This is a scalable system for high spatial resolution of vertical temperature profiles in the troposphere and lower stratosphere, even in the presence of aerosols.

A model study of the effects of winds on concentric rings of gravity waves from a convective plume near Fort Collins on 11 May 2004

[1] Using a convective plume model and a ray trace model, we investigate the effects of winds on concentric rings of gravity waves (GWs) excited from a convective plume on 11 May 2004, near Fort Collins, Colorado. We find that winds can shift the apparent center of the concentric rings at z = 87 km from the plume location. We also find that critical level filtering (for GWs with small phase speeds propagating in the same direction as the wind) and wave reflection (for high-frequency GWs with small horizontal wavelengths propagating in the opposite direction to the wind) prevent many GWs from reaching the OH airglow layer. Additionally, we find that strong winds disrupt the concentric ring patterns, causing distorted ‘‘squashed’’ ring and arc-like patterns instead. Using a zero wind profile and a representative April mean zonal wind profile, we compare our model results with observations of concentric rings at the Yucca Ridge Field Station (40.7N, 104.9W). We find that the model horizontal wavelengths and periods agree reasonably well with the observed data. We also compare the model temperature perturbations with the temperature perturbations calculated from the intensity perturbations. Because the observations show less critical level filtering than from the April wind profile and more critical level filtering than from the zero wind profile, we conclude that the winds on 11 May were likely somewhat smaller than the April zonal wind profile assumed here.

Comparative study of short-term diurnal tidal variability

Examination of the simultaneous temperature measurement from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, not only confirms the existence of the inversion layer but also reveals the global nature of the inversion, suggesting the presence of a transient planetary wave in the mesosphere. The large tidal variability, therefore, is probably a consequence of the interaction between the transient planetary wave and tides. This possibility is investigated by using the NCAR thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) and by comparing model results with the lidar, SABER, and TIMED Doppler Interferometer (TIDI) measurements. With a large transient planetary wave specified at the model lower boundary, the model is able to produce strong diurnal tidal variability comparable to that from the lidar observation, and the modeled temperature inversion is similar to that from the SABER measurement. The model results suggest that the planetary/tidal wave interaction excites nonmigrating tides and modulates the gravity modes and/or the rotational modes of the diurnal migrating tide. Among the nonmigrating tides, the diurnal zonally symmetric (S = 0) component is the strongest, and its interaction with the planetary wave leads to a strong diurnal eastward wave number 1 component.

Spectral structure of laser light scattering revisited: bandwidths of nonresonant scattering lidars

It is well known that scattering lidars, i.e., Mie, aerosol-wind, Rayleigh, high-spectral-resolution, molecular-wind, rotational Raman, and vibrational Raman lidars, are workhorses for probing atmospheric properties, including the backscatter ratio, aerosol extinction coefficient, temperature, pressure, density, and winds. The spectral structure of molecular scattering (strength and bandwidth) and its constituent spectra associated with Rayleigh and vibrational Raman scattering are reviewed. Revisiting the correct name by distinguishing Cabannes scattering from Rayleigh scattering, and sharpening the definition of each scattering component in the Rayleigh scattering spectrum, the review allows a systematic, logical, and useful comparison in strength and bandwidth between each scattering component and in receiver bandwidths (for both nighttime and daytime operation) between the various scattering lidars for atmospheric sensing.

Continuous-wave, all-solid-state, single-frequency 400-mW source at 589 nm based on doubly resonant sum-frequency mixing in a monolithic lithium niobate resonator

Sum-frequency mixing of two cw single-mode Nd:YAG lasers in a doubly resonant congruent lithium niobate resonator generated two TEM(00) beams of single-frequency 589-nm radiation. The primary beam had a power of 400 mW and the secondary beam of approximately 15 mW by use of 320 mW of 1319-nm and 660 mW of 1064-nm Nd:YAG radiation incident on the lithium niobate resonator. This corresponds to an optical power conversion efficiency of more than 40%.

Low-altitude atmospheric wind measurement from the combined Mie and Rayleigh backscattering by Doppler lidar with an iodine filter

This paper briefly discusses the mobile ground-based incoherent Doppler wind lidar system, with iodine filters as receiving frequency discriminators, developed by the Ocean Remote Sensing Laboratory, Ocean University of Qingdao, China. The presented result of wind profiles in October and November 2000, retrieved from the combined Mie and Rayleigh backscattering, is the first report to our knowledge of wind measurements in the troposphere by such a system, where the required independent measurement of aerosol-scattering ratio can also be performed. A second iodine vapor filter was used to lock the laser to absolute frequency reference for both wind and aerosol-scattering ratio measurements. Intercomparison experiments of the lidar wind profile measurements were performed with pilot balloons. Results showed that the standard deviation of wind speed and wind direction, for the 2-4 km altitude range, were 0.985 m/s and 17.9 degrees, respectively.

Na temperature lidar measurements of gravity wave perturbations of wind, density and temperature in the mesopause region

High resolution temperature profiles of the mesopause region above Fort Collins, CO (40.6°N,105°W) were measured with a Na lidar on the nights of March 2–3 and April 15–16, 1990, during the ALOHA-90 campaign. This paper reports the initial scientific analysis of these data which were used to compute (1) the altitude profiles of relative atmospheric temperature perturbations, (2) the mean Brunt-Vaisala frequency in the mesopause region, and (3) the vertical shear variance of horizontal winds. On March 2–3 and April 15–16, the rms temperature perturbations were 5.7% and 7.1%, the average Brunt-Vaisala periods were 4.9 min and 4.6 min, and the wind shear variances were 878 (ms−1/km)² and 967 (ms−1/km)², respectively.