Rayleigh Lidar Observations Research Articles

Quantification of gravity wave forcing in driving the stratospheric Quasi‐Biennial Oscillation

Using long‐term Rayleigh lidar temperature observations during April 1998–April 2005 in the lower stratospheric region, momentum flux divergence of the gravity waves of periods 0.5–1 and 2–4 hours are estimated over Gadanki (13.5°N, 79.2°E), India. Monthly mean zonal winds from NCEP/NCAR reanalysis data over Gadanki at two pressure levels 10 and 20 hPa are used to study the characteristics of the Quasi‐Biennial Oscillation (QBO) and its month‐to‐month acceleration. This observed mean flow acceleration is compared with that estimated from the momentum flux divergence of gravity waves, which led to a better insight into the role of gravity waves in driving the QBO. The present analysis reveals that the contribution of gravity waves towards the westerly phase of QBO varies from ∼10–60% while that during easterly phase from ∼10–30%. The present study thus quantifies the role of gravity waves in driving the easterly and westerly phases of QBO.

Analysis and Characterization of the SSMIS Upper Atmosphere Sounding Channel Measurements

Analyses and results of the radiometric calibration accuracy and measurement characteristics of the first Defense Meteorological Satellite Program (DMSP)'s Special Sensor Microwave Imager/Sounder (SSMIS) upper atmosphere sounding (UAS) channels are presented herein. Launched on October 18, 2003, aboard the DMSP F-16 spacecraft in a sun-synchronous orbit, the SSMIS UAS channels provide the first operational measurements of microwave radiation emitted by the Earth's atmosphere at mesospheric altitudes. The analysis of the SSMIS radiometer absolute calibration and stability is based upon extensive comparisons with a fully polarimetric radiative transfer model (RTM) that solves for all four Stokes parameters using coincident atmospheric temperature profiles derived from collocated Rayleigh lidar observations merged with the European Centre for Medium-Range Weather Forecasting temperature analyses and climatological data sets. The resulting merged profiles provide a physically consistent temperature profile from the surface to 100 km, as needed by the RTMs. The results presented herein of the SSMIS instrument show that significant hardware and scientific technical challenges arise from microwave temperature sounding of the mesosphere. These include the following: 1) addressing the impact of large noise-equivalent temperature difference associated with narrow channel bandwidths; 2) achieving high channel center-frequency stability; 3) compensation of large spacecraft-induced Doppler shift; 4) better characterization of the Zeeman splitting of the oxygen absorption lines; 5) development of a fast polarimetric RTM; and 6) designing stable and accurate on-orbit radiometric calibration targets. Results to date show that the uncertainties of the calibration accuracy of the SSMIS UAS channels are consistent and in agreement with the limits derived for the SSMIS UAS channels and with the simulated radiances derived from the merged lidar profiles.

A quantitative study on the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation

Using a coordinated experimental observation under Middle Atmospheric Dynamics (MIDAS) program, an extensive study is carried out to quantify the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation (SSAO). Rayleigh lidar observations of middle atmospheric temperature over Gadanki (13.5°N, 79.2°E) and rocketsonde wind measurements over Trivandrum (8.5°N, 76.9°E) during the period November 2002 to June 2005 are used for the present study. Gravity waves with periods ranging from 2–4 hours and 0.5–1 hour are found to be dominant in the middle atmosphere throughout the observational period. The altitude profiles of momentum fluxes of gravity waves having these time periods are estimated and their seasonal variations are studied, which showed semiannual variation with maximum around equinoxes and minimum around solstitial months. The mean flow acceleration estimated from the divergence of momentum flux of gravity waves is compared with the mean flow acceleration observed using rocket measured zonal winds during three different cycles of SSAO. This comparison provided an opportunity to quantify the contribution of gravity waves toward generation of SSAO, which is found to be ∼30–50% of the observed acceleration during the evolution of the westerly phase of the SSAO. The present observations showed that the contribution of the gravity waves toward the westerly phase of SSAO varies significantly from cycle to cycle. The significance of the present results lies in quantifying the gravity wave–mean flow interaction during both easterly and westerly phases of SSAO for the first time over this tropical latitude.

Planetary wave and gravity wave influence on the occurrence of polar stratospheric clouds over Davis Station, Antarctica, seen in lidar and radiosonde observations

We present Rayleigh lidar observations of polar stratospheric clouds (PSC) from Davis Station (68.6°S, 78.0°E), Antarctica, from the 2001, 2002, 2003, and 2004 austral winter seasons. The PSC are detected as enhanced backscatter returns at lower stratospheric heights. We use operational radiosonde balloon data to compare the PSC detections with stratospheric temperature and wave properties. As documented by others, we find that the occurrence of PSC is closely tied to average stratospheric temperatures (which, in turn, are closely related to the location of Davis with respect to the Antarctic vortex), with PSC being seen when the temperature falls to near or below the calculated formation temperature of nitric acid trihydrate. There is clear evidence in the sonde data for gravity wave and planetary wave modulation of the stratospheric temperature. We see small‐scale wavelike structure in the PSC profiles, which likely arises from gravity waves, but find little direct correlation between a given (vertical) lidar PSC profile and near‐contemporaneous sonde profile, probably because the sonde flight is not an instantaneous sounding at the exact spatial location of the lidar. The planetary‐wave‐induced temperature variations are of the order of 10 times the size of the gravity wave variations and have a greater and more direct influence in PSC occurrence over Davis.

Lidar observations of middle atmospheric gravity wave activity over a low-latitude site (Gadanki, 13.5° N, 79.2° E)

Abstract. The low-latitude middle atmospheric gravity wave characteristics are presented using 310 nights of Rayleigh lidar observations made at Gadanki (13.5° N, 79.2° E) over the period from March 1998 to December 2002. The gravity wave characteristics are presented in terms of vertical wave number and frequency spectra, along with the estimated potential energy for the four seasons, namely, spring, summer, autumn and winter. The computed wave number spectra for both the stratosphere and the mesosphere are found to differ significantly from a saturated model predicted spectrum. The spectra were found to be shallower at lower wave numbers and steeper at higher wave numbers with transition at ~8.85×10-4 cy/m. The computed frequency spectra seem to follow the model plot with a power law index of -5/3 above a frequency of ~2×10-4 Hz. The estimated potential energy per unit mass increases gradually up to ~60 km and then rather rapidly above this height to reach values of the order of 200J/kg at ~70 km.

Mesospheric temperature inversions over the Indian tropical region

Abstract. To study the mesospheric temperature inversion, daily temperature profiles obtained from the Halogen Occultation Experiment (HALOE) aboard the Upper Atmospheric Research Satellite (UARS) during the period 1991-2001 over the Indian tropical region (0-30° N, 60-100° E) have been analyzed for the altitude range 34-86km. The frequency of occurrence of inversion is found to be 67% over this period, which shows a strong semiannual cycle, with a maximum occurring one month after equinoxes (May and November). Amplitude of inversion is found to be as high as 40K. Variation of monthly mean peak and bottom heights along with amplitude of inversions also show the semiannual cycle. The inversion layer is detected most frequently in the altitude range of 70-85km, with peak height ranging from 80 to 83km and that of the bottom height from 72 to 74km. A comparison of frequency of temperature inversion with that obtained from Rayleigh lidar observations over Gadanki (13.5° N, 60-100° E) is found to be reasonable. The seasonal variation of amplitude and frequency of occurrence of temperature inversion indicates a good correlation with seasonal variation of average ozone concentration over the altitude range of the inversion layer.

Rayleigh lidar observations of quasi‐sinusoidal waves in the tropical middle atmosphere

Rayleigh lidar observations of temperature for ∼2–7 hours on 38 nights during the period of 18 January–5 March 1999 and for ∼3 hours on 29 nights during 29 February–2 April 2000 in the altitude region of 27–60 km over Gadanki (13.5°N, 85°E) clearly show the dominance of the quasi‐sinusoidal waves of periods in the range of ∼6–13 hours in temperature in the tropical middle atmosphere. During 1999, the vertical wavelength of these waves ranges from 7.1 to 17 km with a mean value of 12.0 ± 2.4 km while during 2000 it ranges from 5.5 to 17 km with a mean value of 11.4 ± 3.5 km. The wave periods estimated from the observations during 1999 are generally greater than the observation period on each night and are estimated to be in the range of 6.5–13.1 hours with an average period of 9.7 ± 1.8 hours, which is significantly smaller than the inertial period of 53 hours. The amplitudes of these waves are in the range of 1 to 8 K. Such sinusoidal wave modes are clearly discernible in the temperature profiles for ∼50% nights of observation. Another striking feature is that the quasi‐sinusoidal structure is clearly observed in the “equivalent day” analysis also, indicating only small day‐to‐day variability in phase, a property that is characteristic of atmospheric tides.

Gravity waves in the tropical middle atmosphere: Characteristics and wave-mean flow interaction

High-resolution Rayleigh lidar observations of temperature in the altitude region of 27–60 km over Gadanki (13.5°N, 79.2°E) during the period of January 18 to March 5 1999 and February 29 to March 31 2000 were used to study the gravity wave characteristics in the tropical middle atmosphere. The vertical wavenumber spectra of gravity waves and the altitude variation of the potential energy per unit mass (Ep) associated with gravity wave activity are found to be similar during both these years. Altitude profile of E p indicates that significant wave damping occurs in the stratosphere while nearly non-dissipating gravity wave growth is observed in the lower mesosphere. The slope of the vertical wave number spectra is observed to be about −2.1, which is less than that expected for saturated spectra (−3). The gravity wave activity in the stratosphere and lower mesosphere is found to undergo temporal variations, which are correlated with the temperature fluctuations in the middle atmosphere. A longer period wave with a mean vertical wavelength of about 12.8 km and wave period of about 8–14 hours is also observed on several nights.

First observational evidence of the modulation of gravity wave activity in the low latitude middle atmosphere by equatorial waves

Evidence for the modulation of the gravity wave activity by the equatorial waves in the tropical middle atmosphere is presented using the Rayleigh lidar observations of the temperature over Gadanki (13.5°N, 79.2°E) and the rocketborne measurements of winds over Shriharikota Range (13.7°N, 80.2°E) during the period of 29 February to 31 March, 2000. The potential energy per unit mass associated with the gravity wave activity in the upper stratosphere and mesosphere is found to undergo periodic fluctuations, which is well correlated with the zonal and meridional wind oscillations in the stratosphere produced by the equatorial waves. The most dominant modulation of the gravity wave activity due to equatorial waves is found to occur at periods around 4‐days and 12‐days. Minimum gravity wave activity in the mesosphere is observed during the southward phase of meridional wind and the westward phase of zonal wind oscillations in the lower stratosphere.

Rayleigh lidar observations of a mesospheric inversion layer during night and day

A narrow field of view Rayleigh lidar has been constructed at Millstone Hill / MIT Haystack Observatory (42.6°N, 71.5°W) for observations of middle atmospheric temperatures throughout the diurnal cycle. During a 31.5 h measurement on 19–21 March 2001 a mesospheric thermal inversion layer was observed in both the night and day. It developed near 60 km in altitude, progressed downward at 0.40±0.06 km/h, and had an overlying adiabatic lapse rate. The inversion amplitude correlated with the evolution of stratospheric gravity wave activity, although the mesospheric perturbations were too large to be due to conservative gravity‐wave growth alone. The 24 h mean temperature profile shows no evidence of a residual inversion layer.

Observed coupling of the mesosphere inversion layer to the thermal tidal structure

Rayleigh lidar observations of mesosphere temperature profiles obtained from 40 to ∼100 km from Logan, Utah (41.7, 111.8 W, altitude, 1.9 km) over 10 nights in late February, 1995, revealed an interesting development between 60 to 75 km of a winter mesosphere inversion layer with an amplitude of ∼20–30 K and a downward phase progression of ∼1 km/hr. The data also showed two altitude regions exhibiting significant cooling of 10–30 K in extent. These were located below and above the peak of the inversion layer, respectively, at altitudes of ∼50–55 km and ∼70–80 km. When these results were compared with the predictions of a global wave scale model (GSWM), the observed thermal mesosphere structure is similar to the computed composite tidal structure based upon the semi‐diurnal and diurnal tides with the exception that observed amplitudes of heating and cooling are ∼10x larger than predicted GSWM values. We suggest that these events over Utah are caused through a localized mechanism involving the coupling of gravity waves to the mesopause tidal structure.

Upper mesosphere temperatures in summer: WINDII observations and comparisons

Atmospheric temperature measurements from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS), determined from the observed Rayleigh scattering are presented. Infrared radiances predicted from these profiles are compared with measurements from the Improved Stratospheric and Mesospheric Sounder on UARS for nine cases of spatial and temporal coincidence with an effective difference of about 5–10 K in the height range 70–85 km. A comparison with monthly averaged SME results and Rayleigh lidar temperature observations at mid‐latitudes taken 8 years earlier indicated that WINDII temperatures were cooler on average by 10 K; this is consistent with a temperature decrease of 1.5 K/year inferred from the SME and lidar results. At high latitudes the agreement between falling spheres and WINDII was found to be very good.

A comparison of ambipolar diffusion coefficients in meteor trains using VHF radar and UV lidar

In this paper we present the first comparative estimations of ionic diffusion rates for sporadic meteor trains near the mesopause made using VHF radar and UV Rayleigh lidar observations. In both cases we initially assumed that the meteor trains dissipate primarily through ambipolar diffusion. For the radar data, the diffusion coefficient within the meteor train was determined from the decay rate of the backscattered power. From the the lidar data we then calculated profiles of the atmospheric temperature and density in the height range at which the meteor echoes were detected. These data were used to estimate the ambipolar diffusion coefficients that would result assuming different species of ions. Our results appear consistent with the notion that short‐lived underdense meteor trains in the height range of 85–95 km decay primarily by ambipolar diffusion. However, the diffusion coefficients obtained from the radar observations were smaller than those found from the lidar data assuming metal meteoric ions. One possible explanation could be that the radar meteor echoes resulted from ionized constituents of the atmosphere.

Rayleigh Lidar Observations of Thermal Structure and Gravity Wave Activity in the High Arctic during a Stratospheric Warming

Abstract During February and March 1993, Rayleigh lidar observations of temperature structure and gravity wave activity were carried out in the high Canadian Arctic at Eureka, Northwest Territories (80°N, 86°W). A sudden warming was observed first in the upper stratosphere during late February and then at lower levels in early March. The warming appeared to be part of a disturbance of the entire middle atmosphere with temperature changes in the mesosphere and lower stratosphere being opposite in sign to those in the upper stratosphere. Shorter time and length scale temperature fluctuations, observed in the upper stratosphere, are interpreted as being a result of atmospheric gravity waves. The wave amplitudes are shown to be capable of inducing convective instability. The rms perturbation and available potential energy density show substantial vertical and day-to-day variability in regions of conservative and dissipative growth rates. Vertical growth of the potential energy spectral density is seen to ceas...

Gravity wave activity in the upper stratosphere and lower mesosphere observed with the Rayleigh lidar at Tsukuba, Japan

We delineated the climatological characteristics of the potential energy of gravity waves, Ep, using Rayleigh lidar observations made in 1990–1991 at Tsukuba, Japan (36°N, 140°E). Tendency of large and small values of Ep in winter and summer, respectively, was detected in the upper stratosphere (30–45 km), suggesting annual variation with a winter maximum. This annual cycle seemed to be consistent with lidar observations made in France and UK [Wilson et al., 1991; Mitchell et al., 1991]. The obtained Ep values in the upper stratosphere and lower mesosphere (45–60 km) were rather similar to the French data, despite the large scatter of the Tsukuba values.

Rayleigh Lidar Observations of Gravity Wave Activity in the Upper Stratosphere at Urbana, Illinois

Abstract During 13 nights of Rayleigh lidar measurements at Urbana Illinois in 1984–86, thirty-six quasi-monochromatic gravity waves were observed in the 35–50 km altitude region of the stratosphere. The characteristics of the waves are compared with other lidar and radar measurements of gravity waves and with theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths (λ2) ranged from 2 to 11.5 km and the measured vertical phase velocities (cz) ranged from 10 to 85 cm s−1. The vertical wavelengths and vertical phase velocities were used to infer observed wave periods (Tob) which ranged from 100 to 1000 min and horizontal wavelengths (λx) which ranged firm 70 to 2000 km. There may be errors, in the inferred values of the horizontal wavelengths because they were calculated by assuming that the observed period inferred the intrinsic period. Dominant wave activity was found at vertical wavelengths between 2–4 km and 7–10 km. No significant seasonal variations were evide...

Density fluctuations in the middle atmosphere over Fukuoka observed by an XeF Rayleigh lidar

Rayleigh lidar observations of the molecule density in the upper stratosphere and the lower mesosphere using an XeF laser (351 and 353 nm) were made from April 1985 through March 1986, at Fukuoka, Japan (33.6°N, 130.4°E). The observed density profiles show the existence of waves with wavelengths around 10 km and downward phase velocities between about 0 and 1.2 km/h. In more than half of the cases, the induced wave periods are longer than the inertial period. Analysis shows that the zonal phase velocities of the waves go in the direction opposite to that of the background flow, at least in these cases. The phase velocity and amplitude of the waves show a semiannual variation. The height dependence of the averaged fluctuation amplitude indicates that the energy dissipation of the waves occurs in the observed altitude range.