Gravity Wave Source Variations during the 2009 Stratospheric Sudden Warming

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月15日（火） 国立極地研究所 2階大会議

A Micropulse eye-safe all-fiber molecular backscatter coherent temperature lidar

In this paper, we analyze the performance of an all-fiber, micropulse, 1.5 μm coherent lidar for remote sensing of atmospheric temperature. The proposed system benefits from the recent advances in optics/electronics technology, especially an all-fiber image-reject homodyne receiver, where a high resolution spectrum in the baseband can be acquired. Due to the presence of a structured spectra resulting from the spontaneous Rayleigh-Brillouine scattering, associated with the relevant operating regimes, an accurate estimation of the temperature can be carried out. One of the main advantages of this system is the removal of the contaminating Mie backscatter signal by electronic filters at the baseband (before signal conditioning and amplification). The paper presents the basic concepts as well as a Monte-Carlo system simulation as the proof of concept

Lidar Observations of Elevated Temperatures in Bright Chemiluminescent Meteor Trails During the 1998 Leonid Shower

Seven persistent trails associated with bright fireballs were probed with a steerable Na wind/temperature lidar at Starfire Optical Range, NM during the 17/18 Nov peak of the 1998 Leonid meteor shower. These chemiluminescence 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 masses of the meteors were from 1 g up to 1 kg. CCD images show that the chemiluminescent emissions (including Na and OH) are confined to the walls of a tube, which expands with time by molecular diffusion. Lidar profiles within the trails show that the temperatures are highest at the edges of the tube where the airglow emissions are brightest. Approximately 3 min after ablation, temperatures at the tube walls are 20-50 K warmer than the tube core and background atmosphere. Neither chemical nor frictional heating provides a satisfactory explanation for the observations

Lidar observations of polar mesospheric clouds at South Pole: Seasonal variations

Polar mesospheric clouds (PMCs) were observed above the geographic South Pole by an Fe Boltzmann temperature lidar from 11 Dec 99 to 24 Feb 00. During this 76-day period 297 h of observations were made on 33 different days and PMCs were detected 66.5% of the time. The mean PMC peak backscatter ratio, peak volume backscatter coefficient, total backscatter coefficient, layer centroid altitude, and layer rms width are 50.59 q- 2.33, 2.70 q- 0.12x10 -9 m-•sr -•, 3.61 q- 0.22x10 -6 sr -•, 85.49 q- 0.09 km, and 0.71 q- 0.03 km, respectively. The PMCs are highest near summer solstice when upwelling over the pole is strongest. The altitudes are 2-4 km higher than that typically observed elsewhere, including the North Pole. After solstice the mean altitudes decreases by about 64 m/day as the upwelling weakens.Ope

Lidar Studies of Interannual, Seasonal, and Diurnal Variations of Polar Mesospheric Clouds at the South Pole

Polar mesospheric clouds (PMC) were observed by an Fe Boltzmann temperature lidar at the South Pole in the 1999–2000 and 2000–2001 austral summer seasons. We report the study of interannual, seasonal, and diurnal variations of PMC using more than 430 h of PMC data. The most significant differences between the two seasons are that in the 2000– 2001 season, the PMC mean total backscatter coefficient is 82% larger and the mean centroid altitude is 0.83 km lower than PMC in the 1999–2000 season. Clear seasonal trends in PMC altitudes were observed at the South Pole where maximum altitudes occurred around 10–20 days after summer solstice. Seasonal variations of PMC backscatter coefficient and occurrence probability show maxima around 25–40 days after summer solstice. Strong diurnal and semidiurnal variations in PMC backscatter coefficient and centroid altitude were observed at the South Pole with both in-phase and out-of-phase correlations during different years. A significant hemispheric difference in PMC altitudes was found, that the mean PMC altitude of 85.03 km at the South Pole is about 2–3 km higher than PMC in the northern hemisphere. Through comparisons with the NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM), the hemispheric difference in PMC altitude is attributed to the hemispheric differences in the altitudes of supersaturation region and in the upwelling vertical wind, which are mainly caused by different solar forcing in two hemispheres that the solar flux in January is 6% greater than the solar flux in July due to the Earth’s orbital eccentricity. Gravity wave forcing also contributes to these differences.Ope

Observations of Persistent Leonid Meteor Trails. 1. Advection of the Diamond Ring

From a single image of a persistent trail left by a -1.5 magnitude Leonid meteor on November 17, 1998, the relative winds between 92.5 and 98 km altitude are derived, where the altitudes are determined by a sodium lidar. These are converted to true winds 82 sec after the appearance of the meteor by fixing the winds at 98 km to match the results of following the trail with the lidar for twelve minutes. The image and winds reveal a fine example of the effects of a gravity wave having a vertical wavelenth of 5.50 ± 0.02 km, a horizontal wavelength of 2650 ± 60 kin, an intrinsic period of 19.5 ± 0.4 hours, and an observed period of 8.6 ± 0.1 hours. Effects of the gravity wave are still present in the wind field 70 rain later

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

An Fe Boltzmann temperature lidar was used to obtain the first measurements of middle atmosphere temperatures, Fe densities, and polar mesosphericlouds (PMCs) over the North and South Poles during the 1999-2000 summer 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 profiles 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 -a. Sporadic Fe (Fes) layers were observed at both Poles with peak densities at 106 km altitude. The maximum densities of the Fes layers were 232x10 a cm -a at North Pole and 6.52x10 a cm -a at South Pole. PMCs were detected above both Poles. The altitudes of PMCs over the South Pole were consistently 2-3 km higher than those observed over the North Pole.Ope

Sodium layer at 110-130 km heights observed above Syowa Station in Antarctic

第3回極域科学シンポジウム　横断セッション「中層大気・熱圏」 11月26日（月）、27日（火） 国立極地研究所 ２階ラウン

Observations of persistent Leonid meteor trails 3. The ‘‘Glowworm’’

A spectacular, well-observed Leonid meteor of visual magnitude -14.3 appeared on 17 November 1998 and left a lingering trail, dubbed the Glowworm, that was well studied. From a location on Kirtland Air Force Base, near Albuquerque, New Mexico, we obtained CCD images of the trail from 94 to 203 s after the meteor and recorded a video with an intensified camera for even longer. From information obtained with a sodium lidar half an hour after the meteor, we have determined that a gravity wave with a vertical wavelength of 2.4 km was responsible for the right-angled appearance of the trail. The trail ended abruptly at 85 km, and its uppermost altitude may have been no greater than 91 km. We designate the Glowworm a Type I trail: one that is wide (1 km), cloudy in appearance, has high diffusion rates (800m2 s-1), high total line emission rates (1.5 x 1018 photons m-1 s-1), and is optically thicker than Type II trails. The lower parts of the Diamond Ring, another Leonid lingering trail that appeared 38 min earlier than the Glowworm, define the Type II trails, which appear as narrow, optically thinner parallel trails, with low diffusion rates (12 m2 s-1) and total line emission rates (1–3 x 1016 photons m1 s-1). No explanation is offered for the two orders of magnitude difference in these quantities. The Glowworm meteor produced infrasound [ReVelle and Whitaker, 1999], from which a meteoroid mass estimate of 522 g was made. We compare our photometry to a detailed numerical modeling of the shape of the trail and emission from the Glowworm made by Zinn et al. [1999], who find that the largest contributors to emission recorded by our CCD and video cameras are atmospheric O2 vibrational bands. Compared to our measurements, their calculated emission is too high by two orders of magnitude, but since most of O2 emission may be absorbed by atmospheric O2 before it reaches the ground, this may indeed be the primary contributor to the observed flux. Although the calculations of Zinn et al. lead to a hollow cylinder appearance which may be appropriate for the Glowworm, it is not pronounced enough to account for the complete darkness between the parallel structures seen in Type II trails. An upper limit to backscattering from dust of 3.7 x 10-5 of the expected return was found from directing a 180 W copper vapor laser at the Glowworm

Lidar Observations of Stratospheric Gravity Waves From 2011 to 2015 at McMurdo (77.84°S, 166.69°E), Antarctica: 2. Potential Energy Densities, Lognormal Distributions, and Seasonal Variations

Five years of Fe Boltzmann lidar's Rayleigh temperature data from 2011 to 2015 at McMurdo are used to characterize gravity wave potential energy mass density (Epm), potential energy volume density (Epv), vertical wave number spectra, and static stability N² in the stratosphere 30–50 km. Epm (Epv) profiles increase (decrease) with altitude, and the scale heights of Epv indicate stronger wave dissipation in winter than in summer. Altitude mean (Formula presented.) and (Formula presented.) obey lognormal distributions and possess narrowly clustered small values in summer but widely spread large values in winter. (Formula presented.) and (Formula presented.) vary significantly from observation to observation but exhibit repeated seasonal patterns with summer minima and winter maxima. The winter maxima in 2012 and 2015 are higher than in other years, indicating interannual variations. Altitude mean (Formula presented.) varies by ~30–40% from the midwinter maxima to minima around October and exhibits a nearly bimodal distribution. Monthly mean vertical wave number power spectral density for vertical wavelengths of 5–20 km increases from summer to winter. Using Modern Era Retrospective Analysis for Research and Applications version 2 data, we find that large values of (Formula presented.) during wintertime occur when McMurdo is well inside the polar vortex. Monthly mean (Formula presented.) are anticorrelated with wind rotation angles but positively correlated with wind speeds at 3 and 30 km. Corresponding correlation coefficients are −0.62, +0.87, and +0.80, respectively. Results indicate that the summer-winter asymmetry of (Formula presented.) is mainly caused by critical level filtering that dissipates most gravity waves in summer. (Formula presented.) variations in winter are mainly due to variations of gravity wave generation in the troposphere and stratosphere and Doppler shifting by the mean stratospheric winds