Xinzhao Chu

Fe Boltzmann temperature lidar: design, error analysis, and initial results at the north and south poles.

The design, development, and first measurements of a novel mesospheric temperature lidar are described. The lidar technique employs mesospheric Fe as a fluorescence tracer and relies on the temperature dependence of the population difference of two closely spaced Fe transitions. The principal advantage of this technique is that robust solid-state broadband laser source(s) can be used that enables the lidar to be deployed at remote locations and aboard research aircraft. We describe the system design and present a detailed analysis of the measurement errors. Correlative temperature observations, made with the Colorado State University Na lidar at Fort Collins, Colorado, are also discussed. Last, we present the initial range-resolved temperature measurements in the mesosphere and lower thermosphere over both the North and the South Poles obtained with this system.

Stratospheric gravity wave characteristics and seasonal variations observed by lidar at the South Pole and Rothera, Antarctica

� 0.7 m s � 1 , and period of � 104 min. Approximately 44% of the observed waves show an upward phase progression while the rest display a downward phase progression in ground-based reference for both locations. Gravity wave potential energy density (GW-EP) at Rothera is � 4 times higher than the South Pole in winter but is comparable in summer. Clear seasonal variations of GW-EP are observed at Rothera with the winter average being 6 times larger than that of summer. The seasonal variations of GW-EP at the South Pole are significantly smaller than those at Rothera. The absence of seasonal variations in wave sources and critical level filtering at the South Pole is likely to be responsible for the nearly constant GW-EP. The minimum critical level filtering in winter at Rothera is likely to be a main cause for the winter enhanced GW-EP, as this would allow more orography-generated waves to reach the 30 to 45 km range. The stratospheric jet streams may also contribute to the winter enhancement at Rothera.

First Lidar Observations of Middle Atmosphere Temperatures, Fe Densities, and Polar Mesospheric Clouds Over the North and South Poles

AnFeBoltzmanntemperaturelidarwasusedto obtaintherstmeasurementsofmiddleatmospheretemper- atures, Fe densities, and polar mesospheric clouds (PMCs) over the North and South Poles during the 1999-2000 sum- mer seasons. The measured temperature structure of the mesopause and lower thermosphere regions in mid-summer at both Poles is consistent with the MSIS90 model. The density proles of the normal Fe layer between 80-100 km at summer solstice are similar at both the North and South Poles with maximum densities of about 2000 cm 3 .S po- radic Fe (Fes) layers were observed at both Poles with peak densities at 106 kmaltitude. The maximum densities of the Feslayers were 23210 3 cm 3 at North Pole and 6.5210 3 cm 3 atSouthPole. PMCsweredetectedabovebothPoles. ThealtitudesofPMCsovertheSouthPolewereconsistently 2-3 km higher than those observed over the North Pole.

Responses of mesosphere and lower thermosphere temperatures to gravity wave forcing during stratospheric sudden warming

[1] We examine the responses of the mesosphere and lower thermosphere (MLT) temperatures to gravity waves (GWs) during stratospheric sudden warming (SSW) using TIME-GCM through modifying GW parameters. Our study confirms that the height of GW forcing region is mainly determined by GW amplitude and wavelength, and its vertical depth is closely tied to the spectral width of GW phase speed. The GW forcing controls the pattern and strength of residual circulation and thereby the characteristics of the MLT cooling and warming regions. The planetary wave (PW) forcing in the MLT also affects the vertical depth and magnitude of MLT temperature anomalies through further modifying the residual circulation. These PWs in MLT are likely generated in-situ by the GW forcing at high latitudes. Therefore, the mechanisms of GW controlling the MLT temperature during a SSW are directly through GW forcing and indirectly through generating PWs in-situ.

Nocturnal thermal structure of the mesosphere and lower thermosphere region at Maui, Hawaii (20.7°N), and Starfire Optical Range, New Mexico (35°N)

The nighttime thermal structure of the mesosphere and lower thermosphere (MLT) region at the Starfire Optical Range (SOR), New Mexico (35.0°N, 106.5°W), and at Maui, Hawaii (20.7°N, 156.3°W), are characterized using Na lidar observations. Both locations exhibit mesospheric temperature inversion layers (MILs) between 85 and 100 km that are not predicted by the MSIS-00 model. The amplitudes of the Maui MILs (∼5.8 K) are about half of those at SOR (∼9.8 K), and the Maui MILs have a smaller width (∼11.1 km) compared to the SOR MILs (∼14.5 km). The Maui lidar temperatures are generally warmer than the MSIS-00 predictions, while the SOR lidar data are comparable to the MSIS-00, except in the MIL altitude range. Both SOR and Maui mesopause temperatures are coldest in midsummer and are warmest during the mesopause transition periods. However, the Maui mesopause is warmer than the SOR, and the amplitude of the mesopause temperature variations at Maui (∼9 K) is much smaller than at SOR (∼19 K). Two distinct levels of mesopause altitudes are clearly shown in the SOR seasonal data with a low altitude around 86.5 km in summer (May through August) and a high altitude around 101 km during the rest of the year. Abrupt transitions between the two stable levels occur in early May and early September. The lidar measurements indicate a low mesopause altitude near 87.5 km in July at Maui when averaging over a 10-hour period centered at local midnight.

Measurements of the vertical fluxes of atomic Fe and Na at the mesopause: Implications for the velocity of cosmic dust entering the atmosphere

The downward fluxes of Fe and Na, measured near the mesopause with the University of Colorado lidars near Boulder, and a chemical ablation model developed at the University of Leeds, are used to constrain the velocity/mass distribution of the meteoroids entering the atmosphere and to derive an improved estimate for the global influx of cosmic dust. We find that the particles responsible for injecting a large fraction of the ablated material into the Earths upper atmosphere enter at relatively slow speeds and originate primarily from the Jupiter Family of Comets. The global mean Na influx is 17,200 ± 2800 atoms/cm2/s, which equals 298 ± 47 kg/d for the global input of Na vapor and 150 ± 38 t/d for the global influx of cosmic dust. The global mean Fe influx is 102,000 ± 18,000 atoms/cm2/s, which equals 4.29 ± 0.75 t/d for the global input of Fe vapor.

Vertical evolution of potential energy density and vertical wave number spectrum of Antarctic gravity waves from 35 to 105 km at McMurdo (77.8°S, 166.7°E)

We report the first characterization of potential energy densities and vertical wave number spectra of Antarctic gravity waves (GWs) from 35 to 105 km, derived from Fe lidar temperature measurements at McMurdo (77.8°S, 166.7°E) in 2011–2013 winters. For GWs with periods of 2–10 h, the potential energy density per unit volume (Epv) decreases by 2 orders of magnitude from 35 to 105 km, while that per unit mass (Epm) increases from several to hundreds of J/kg. Epm increases with a mean scale height of ~10.4 km in the Rayleigh region (35–65 km) and of ~13.2 km in the Fe region (81–105 km), and of particular interest is the inferred severe dissipation in between (65–81 km). Overall, the vertical evolutions of Epv and Epm indicate considerable wave energy loss from the stratosphere to the lower thermosphere. The vertical wave number spectra exhibit power law forms for vertical wavelengths λz   10 km in 35–60 km. PSDs increase by 1 order of magnitude from the stratosphere to the lower thermosphere. Using higher temporal resolution data to include 0.5–2 h waves increase Epm by ~25–45% and increase PSDs of 2–5 km waves by a factor of 2 and of >10 km waves by less than 50%.

Lidar observations of elevated temperatures in bright chemiluminescent meteor trails during the 1998 Leonid Shower

Seven persistent trails associated with bright reballs were probedwith asteerable Nawind/temperature lidar at Starre Optical Range, NM during the 17/18 Nov peak of the 1998 Leonid meteor shower. These chemilu- minescence trails were especially rich in Na. The average Na abundance within the trails was 52% of the background Na layer abundance, which suggests that the corresponding massesofthemeteorswerefrom1gupto1kg. CCDimages showthatthechemiluminescentemissions(includingNaand OH)areconnedtothewalls ofatube, whichexpandswith time by molecular diusion. Lidar proles within the trails show that the temperatures are highest at the edges of the tube where the airglow emissions are brightest. Approxi- mately 3 min after ablation, temperatures at the tube walls are 20{50 K warmer than the tube core and background at- mosphere. Neither chemical nor frictional heating provides a satisfactory explanation for the observations.

Lidar observations of persistent gravity waves with periods of 3–10 h in the Antarctic middle and upper atmosphere at McMurdo (77.83°S, 166.67°E)

Persistent, dominant, and large-amplitude gravity waves with 3–10 h periods and vertical wavelengths ~20–30 km are observed in temperatures from the stratosphere to lower thermosphere with an Fe Boltzmann lidar at McMurdo, Antarctica. These waves exhibit characteristics of inertia-gravity waves in case studies, yet they are extremely persistent and have been present during every lidar observation. We characterize these 3–10 h waves in the mesosphere and lower thermosphere using lidar temperature data in June from 2011 to 2015. A new method is applied to identify the major wave events from every lidar run longer than 12 h. A continuous 65 h lidar run on 28–30 June 2014 exhibits a 7.5 h wave spanning ~60 h, and 6.5 h and 3.4 h waves spanning 40 and 45 h, respectively. Over the course of 5 years, 323 h of data in June reveal that the major wave periods occur in several groups centered from ~3.5 to 7.5 h, with vertical phase speeds of 0.8–2 m/s. These 3–10 h waves possess more than half of the spectral energy for ~93% of the time. A rigorous prewhitening, postcoloring technique is introduced for frequency power spectra investigation. The resulting spectral slopes are unusually steep (−2.7) below ~100 km but gradually become shallower with increasing altitude, reaching about −1.6 at 110 km. Two-dimensional fast Fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20–30 km across periods of 3.5–10 h. These statistical features shed light on the wave source and pave the way for future research.

Observations of Persistent Leonid Meteor Trails 2. Photometry and Numerical Modeling

During the 1998 Leonid meteor shower, multi-instrument observations of persistent meteor trains were made from the Starfire Optical Range on Kirtland Air Force Base, New Mexico, and from a secondary site in nearby Placitas, New Mexico. The University of Illinois Na resonance lidar measured the Na density and temperature in the trains, while various cameras captured images and videos of the trains, some of which were observed to persist for more than 30 min. The Na density measurements allow the contribution of Na airglow to the observed train luminescence to be quantified for the first time. To do this, persistent train luminescence is numerically modeled. Cylindrical symmetry is assumed, and observed values of the Na density, temperature, and diffusivity are used. It is found that the expected Na luminosity is consistent with narrowband CCD all-sky camera observations, but that these emissions can contribute only a small fraction of the total light observed in a 0.5–1 μ bandwidth. Other potential luminosity sources are examined, in particular, light resulting from the possible excitation of monoxides of meteoric metals (particularly FeO) and O2(b1∑g+) during reactions between atmospheric oxygen species and meteoric metals. It is found that the total luminosity of these combined processes falls somewhat short of explaining the observed brightness, and thus additional luminosity sources still are needed. In addition, the brightness distribution, the so-called hollow cylinder effect, remains unexplained.