Chemical Transport of Neutral Atmospheric Constituents by Waves and Turbulence: Theory and Observations

Vertical chemical transport occurs when the density fluctuations of a species, caused by perturbations of its chemistry, are strongly correlated with the vertical wind fluctuations. Chemical transport can exceed dynamical and eddy transport of chemically active species. Theoretical expressions are derived for the chemical fluxes and transport velocities and used to characterize the vertical transport of mesospheric O3 and meteoric Na and Fe between 85 and 100 km. Chemical transport is dependent on the intrinsic frequency spectrum of the temperature fluctuations and on the chemical cutoff periods of the species. For O3 only high-frequency fluctuations contribute to chemical transport because slower, larger-amplitude density perturbations are damped by chemistry. The cutoff periods for O3 range from ~15 min during the day when photolysis is important to ~200 min at night. The chemical transport velocities of Na and Fe are proportional to the O3, O2+, and NO+ densities above 85 km. For O3, Na, and Fe the magnitudes of the vertical transport velocity can be as large as 10 cm/s, and they exhibit strong diurnal variations. O3 chemical transport is downward at night and upward during the day. Na and Fe chemical transport are largely upward with the strongest upward velocities at night near 85 and 100 km

A COMPARISON OF PRE-COLLEGE ENRICHMENT PROGRAM PARTICIPANTS AND NON-PARTICIPANTS: COLLEGE ACADEMIC PERFORMANCE MEASURES

This paper analyzes College Grade Point Averages (CGPAs), American College Testing Composite (ACTC) scores and Scholastic Assessment Test Total (SATT) scores of over 1,300 undergraduates at West Virginia University (WVU) who participated in the Health Sciences and Technology Academy (HSTA) to those students who did not (Non-HSTA). Traditionally, pre-college enrichment programs provide academic enrichment to underrepresented youth with the intent of increasing their chances for post-secondary entry and success. Factorial design determined if HSTA participants were better prepared to pursue postsecondary study. Overall, the results reveal that HSTA students outperformed their Non-HSTA counterparts in that there were significant differences in the overall CGPA, ACTC and SATT scores

A Comparison of Academic Performance Measures of HSTA Participants with Non-HSTA Participants: Is It Possible to Narrow the African American-White Achievement Gap?

Historically, African American and other underserved students encounter academic challenges in pursuit of a college degree—one of which is their performance on standardized tests. This paper analyzes College Grade Point Averages (CGPAs), ACT Composite (ACTC), and SAT Total (SATT) scores of students who participated in the Health Sciences and Technology Academy (HSTA), an out-of-school-time (OST) program, and Non-HSTA (NHSTA) students attending West Virginia University. Traditionally, OST programs provide academic enrichment to underserved youth to increase their chances for post-secondary entry and success. Two-Way Factorial ANOVA determined if HSTA participants performed better on academic measures than their NHSTA counterparts. The ANOVAs showed statistically significant differences based on Status (HSTA/NHSTA) and Race (African American/White) on the SATT and ACTC. Although not statistically significant, there are favorable outcomes on the CGPA for African American HSTA students comparable to their Non-HSTA counterparts

Vertical Dynamical Transport of Mesospheric Constituents by Dissipating Gravity Waves

Over 400 h of Na wind/temperature lidar observations, obtained at the Star5re Optical Range, NM, are used to study the vertical dynamical transport of Na in the mesopause region between 85 and 100 km. Dynamical transport occurs when dissipating, non-breaking gravity waves impart a net vertical displacement in atmospheric constituents as they propagate through a region. We show that the vertical constituent flux can be related in a simple way to the vertical heat flux. Breaking gravity waves also contribute to eddy transport by generating turbulence. Because eddy transport is a mixing process, it only occurs in the presence of a gradient in the concentration profile of the constituent, while dynamical transport can be sustained even in the absence of such a gradient. The dynamical Na flux is compared with the predicted eddy flux. The maximum downward dynamical flux of Na is −280 m/s cm3 at 88 km. The maximum downward eddy flux is −160 m/s cm3 at the same altitude assuming the diffusion coefficient is 200 m2/s. The observational results are consistent with theoretical predictions below 93 km and show that dynamical transport often exceeds the vertical transport associated with eddy diffusion. The theoretical models are used to predict the dynamical and eddy fluxes of atomic oxygen and show that for this constituent, dynamical transport is also a signifcant transport mechanism

Seasonal Variations of the Vertical Fluxes of Heat and Horizontal Momentum in the Mesopause Region at Starfire Optical Range, New Mexico

Lidar observations of wind and temperature profiles between 85 and 100 km, conducted at the Starfire Optical Range (SOR), New Mexico, are used to characterize the seasonal variations of the vertical fluxes of heat and horizontal momentum and their relationships to gravity wave activity in this region. The wind and temperature variances exhibit strong 6-month oscillations with maxima during the summer and winter that are about 3 times larger than the spring and fall minima. The vertical heat flux also exhibits strong 6-month oscillations with maximum downward flux during winter and summer. The downward heat flux peaks near 88 km where it exceeds -3 K m s-1 in mid-winter and is nearly zero during the spring and fall equinoxes. The heat flux is significantly different from zero only when the local instability probability exceeds 8%, i.e., the annual mean for the mesopause region. The momentum fluxes also exhibit strong seasonal variations, which are related to the horizontal winds. Two-thirds of the time the horizontal momentum flux is directed against the mean wind field

Vertical Heat and Constituent Transport in the Mesopause Region by Dissipating Gravity Waves at Maui, Hawaii (20.7ºN), and Starfire Optical Range, New Mexico (35ºN)

Vertical heat flux profiles induced by dissipating gravity waves in the mesopause region (85–100 km altitude) are derived from Na lidar measurements of winds and temperatures at Maui (20.7ºN, 156.3ºW), Hawaii, and compared with earlier results from Starfire Optical Range (SOR, 35.0ºN, 106.5ºW), New Mexico. The heat flux profile at SOR has a single downward maximum of 2.25 ± 0.3 K m/s at 88 km, while the profile at Maui has two downward maxima of 1.25 ± 0.5 K m/s and 1.40 ± 0.5 K m/s at 87 and 95 km, respectively. The common maximum below 90 km can be attributed to high probability of convective instability. Comparison of the horizontal wind shear suggests that the second maximum at 95 km at Maui may be associated with dynamic instability. The measured Na flux and predicted Na flux based on measured heat flux at Maui agree well, further confirming earlier findings using SOR data. The dynamical flux of atomic oxygen estimated from the heat flux is smaller at Maui compared with that at SOR, but both are comparable to or larger than the eddy flux. The results also suggest that weaker gravity wave dissipation at Maui may cause two opposite effects on the energy balance in the mesopause region, a reduced cooling from heat transport and reduced chemical heating from atomic oxygen transport

First Na Lidar Measurements of Turbulence Heat Flux, Thermal Diffusivity, and Energy Dissipation Rate in the Mesopause Region

Turbulence is ubiquitous in the mesopause region, where the atmospheric stability is low and wave breaking is frequent. Measuring turbulence is challenging in this region and is traditionally done by rocket soundings and radars. In this work, we show for the first time that the modern Na wind/temperature lidar located at Andes Lidar Observatory in Cerro Pachón, Chile, is able to directly measure the turbulence perturbations in temperature and vertical wind between 85 and 100 km. Using 150 h of lidar observations, we derived the frequency (ω) and vertical wave number (m) spectra for both gravity wave and turbulence, which follow the power law with slopes consistent with theoretical models. The eddy heat flux generally decreases with altitude from about −0.5 Km s−1 at 85 km to −0.1 Km s−1 at 100 km, with a local maximum of −0.6 Km s−1 at 93 km. The derived mean turbulence thermal diffusivity and energy dissipation rate are 43 m2 s−1 and 37 mW kg−1, respectively. The mean net cooling resulted from the heat transport and energy dissipation is −4.9 ± 1.5 K d−1, comparable to that due to gravity wave transport at −7.9 ± 1.9 K d−1. Turbulence key parameters show consistency with turbulence theories

Atmospheric Stability and Gravity Wave Dissipation in the Mesopause Region

High-resolution temperature profile data collected at the Urbana Atmospheric Observatory (40ºN, 88ºW) and Starfire Optical Range, NM (35ºN, 106.5ºW) with a Na lidar are used to assess the stability of the mesopause region between 80 and 105 km. The mean diurnal and annual temperature profiles demonstrate that in the absence of gravity wave and tidal perturbations, the background atmosphere is statically stable throughout the day and year. Thin layers of instability can be generated only when the combined perturbations associated with tides and gravity waves induce large vertical shears in the horizontal wind and temperature profiles. There is a region of reduced stability below the mesopause between 80 and 90 km where the temperature lapse rate is large and the buoyancy parameter N2 is low. The vertical heat flux is maximum in this region which suggests that this is also a region of significant wave dissipation. There is also a region of enhanced stability above 95 km in the lower thermosphere where N2 is large. There appears to be little wave dissipation above 95 km because the temperature variance increases rapidly with increasing altitude in this region and the vertical heat flux is zero

Measurements of Atmospheric Stability in the Mesopause Region at Starfire Optical Range, NM

The structure and seasonal variations of static (convective) and dynamic (shear) instabilities in the mesopause region (80–105 km) are examined using high-resolution wind and temperature data obtained with a Na lidar at the Starfire Optical Range, NM. The probabilities of static and dynamic instability are sensitive functions of N2/S2, where N is the buoyancy frequency and S is the total vertical shear in the horizontal winds. The mesopause region is most stable in summer when the mesopause is low, N is large and S is small. Monthly mean N2/S2 varies from a maximum value of about 1.06 in mid-summer to a minimum of 0.68 in January. The annual mean values of N and S are, respectively, 0.021 s−1 and 23 ms−1 km−1. The probabilities of static and dynamic instabilities are maximum in mid-winter when they average about 10% and 12%, respectively, and are minimum in summer when they average about 7% and 5%, respectively. The observations are generally consistent with theoretical predictions based on Gaussian models for the temperature and wind fluctuations induced by gravity waves. They also show that statically unstable conditions are generally preceded by dynamically unstable conditions. The instability probabilities vary considerably from night to night and the structure of the unstable regions are significantly influenced by atmospheric tides. Tides alone are usually not strong enough to induce instability but they can establish the environment for instabilities to develop. As the tidal temperature perturbations propagate downward, they reduce the stability on the topside of the positive temperature perturbation. Instabilities are then induced as gravity waves propagate through this layer of reduced static stability

Seasonal and Nocturnal Variations of the Mesospheric Sodium Layer at Starfire Optical Range, New Mexico

The seasonal variations of the mesospheric sodium layer structure over Starfire Optical Range (SOR: 35ºN, 106.5ºW), New Mexico are characterized using 46 night data of Na wind/temperature lidar observations collected from Jan. 1998 to May 2000. The column abundance has a mean value of 5.06 x 109 cm -2 and strong annual oscillations of with a maximum in November and a minimum in June and July. The annual mean rms width of the sodium layer is 4.30 km and the mean centroid height is 91.60 km. Semiannual oscillations are evident in seasonal variations of the rms width and the centroid height. Their mean nocturnal variations show effects of tides. The photo-ionization during daytime and recombination processes of Na at night, as well as tidal dynamics, induce strong nocturnal variations in the sodium abundance with a minimum just before midnight and a maximum just before sunrise