Gravity-wave influences on Arctic mesospheric clouds as determined by a Rayleigh lidar at Sondrestrom, Greenland (original) (raw)
Related papers
Journal of Geophysical Research: Atmospheres, 2012
1] The effects of atmospheric gravity waves (AGWs) on Polar Mesospheric Cloud (PMC) evolution and brightness are studied using a two dimensional version of the Community Aerosol and Radiation Model for Atmospheres (CARMA 2D). The primary objectives for doing CARMA modeling of AGW effects on PMCs are to address the question of whether AGWs can account for the rapid, orbit by orbit changes in cloud structure and brightness seen in overlapping regions from images of the Cloud Imaging and Particle Size (CIPS) experiment on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft. We present comparisons of PMC brightness changes between our numerical simulations and observations from the CIPS experiment. Previous modeling studies have indicated a much longer life-time for PMC than the 90 min between CIPS orbits. We present CARMA 2D results showing dependence of ice particle growth and PMC brightness on AGW perturbation of background temperatures and water vapor concentrations. The model shows differences in brightness of PMCs due to differences in number of large ice particles depending on the scale and periods of the AGWs and also indicates that overall cloud brightness is a function of the wave period. While the maximum rate of change in PMC brightness from the model is still almost a factor of two less than the CIPS observed maximum rate of change in brightness, our study indicates that the variation in PMC brightness is in part due to the upward transport of water vapor into water depleted region by AGWs and the growth of ice particles from sub visual to visual and to larger sizes than they normally would have without AGWs. The presence of short period AGW cause periodic oscillations in cloud brightness about the no-AGW brightness while long-period AGW can temporarily increase the brightness of PMCs compared to the PMC brightness under no-AGW case. However, both the short-period and long-period AGW ultimately reduce the domain averaged PMC brightness in the long-term. This agrees with CIPS observations of generally dimmer PMCs in regions of high AGW activity. The seasonal variation in PMC albedos and the day to day variations seen in CIPS can be reproduced using a spectrum of short and long period AGW.
Journal of Geophysical Research, 2010
The Cloud Imaging and Particle Size (CIPS) experiment is one of three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into a 600 km sun-synchronous orbit on April 25, 2007. CIPS images have shown distinct wave patterns and structures in Polar Mesospheric Clouds (PMC), around the summertime mesopause region, which are qualitatively similar to structures seen in Noctilucent Clouds (NLC) from ground-based photographs. The structures in PMC are generally considered to be manifestations of upward propagating atmospheric gravity waves (AGW). Variability of AGW effects on PMC reported at several lidar sites has led to the notion of longitudinal differences in this relationship. This study compares the longitudinal variability in the CIPS observed wave occurrence frequency with CIPS measured PMC occurrence frequency and albedo along with mesospheric temperatures measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) spacecraft. Our results for the latitude ranges between 70 o -80 o show a distinct anticorrelation of wave structures with cloud occurrence frequency and correlations with temperature perturbations for at least two of the four seasons analyzed, supporting the idea of gravity wave induced cloud sublimation. The locations of the observed wave events show regions of high wave activity in both hemispheres. In the northern hemisphere, while the longitudinal variability in observed wave structures show changes from the 2007 to 2008 seasons, there exist regions of both low and high wave activity common to the two seasons. These persistent features may explain some of the observed differences in PMC activity reported by ground-based lidar instruments distributed at different longitudes. The statistical distribution of horizontal scales increases with wavelength up to at least 250 km. We also discuss the possibility of atmospheric tides, especially the nonmigrating semidiurnal tide, aliasing our observations and affecting the results presented in this analysis. suitable for water ice formation. Rapp and Thomas [2006] provided a review of the microphysics of
A case study of gravity waves in noctilucent clouds
Annales Geophysicae, 2004
We present a case study of a noctilucent cloud (NLC) display appearing on 10-11 August 2000 over Northern Sweden. Clear wave structures were visible in the clouds and time-lapse photography was used to derive the parameters characterising the gravity waves which could account for the observed NLC modulation. Using two nearby atmospheric radars, the Esrange MST Radar data and Andoya MF radar, we have identified gravity waves propagating upward from the upper stratosphere to NLC altitudes. The wave parameters derived from the radar measurements support the suggestion that gravity waves are responsible for the observed complex wave dynamics in the NLC.
Modelling the effects of gravity waves on stratocumulus clouds observed during VOCALS-UK
Atmospheric Chemistry and Physics, 2013
During the VOCALS campaign spaceborne satellite observations showed that travelling gravity wave packets, generated by geostrophic adjustment, resulted in perturbations to marine boundary layer (MBL) clouds over the southeast Pacific Ocean (SEP). Often, these perturbations were reversible in that passage of the wave resulted in the clouds becoming brighter (in the wave crest), then darker (in the wave trough) and subsequently recovering their properties after the passage of the wave. However, occasionally the wave packets triggered irreversible changes to the clouds, which transformed from closed mesoscale cellular convection to open form. In this paper we use large eddy simulation (LES) to examine the physical mechanisms that cause this transition. Specifically, we examine whether the clearing of the cloud is due to (i) the wave causing additional cloud-top entrainment of warm, dry air or (ii) whether the additional condensation of liquid water onto the existing drops and the subsequent formation of drizzle are the important mechanisms. We find that, although the wave does cause additional drizzle formation, this is not the reason for the persistent clearing of the cloud; rather it is the additional entrainment of warm, dry air into the cloud followed by a reduction in longwave cooling, although this only has a significant effect when the cloud is starting to decouple from the boundary layer. The result in this case is a change from a stratocumulus to a more patchy cloud regime. For the simulations presented here, cloud condensation nuclei (CCN) scavenging did not play an important role in the clearing of the cloud. The results have implications for understanding transitions between the different cellular regimes in marine boundary layer (MBL) clouds.
Non-equilibrium compositions of liquid polar stratospheric clouds in gravity waves
Geophysical Research Letters, 2000
On 25 January 1998 mountain induced gravity waves developed over Scandinavia leading to the formation of mesoscale polar stratospheric clouds (PSCs). Balloonborne mass spectrometric measurements of particle composition and optical backscatter measurements were performed above Kiruna/Sweden. PSCs were encountered twice, showing a correlated increase in the condensed phase water, nitric acid and the backscatter ratio. Thermodynamic modeling allows the PSC particles to be unambiguously identified as supercooled ternary solution (STS) droplets, but cannot account for the measured scatter in the particulate HNO3:H20 mole ratio. Simultaneous temperature measurements show that the particles were subject to rapid atmospheric temperature fluctuations of q-1 K and cooling/heating rates exceeding 1K/rain caused by the gravity waves. Micro-physical non-equilibrium modeling of STS droplet distributions reveals that the observed temperature perturbations cause particle compositions in close agreement with the measured HNO3:H20 variations. Non-equilibrium compositions of liquid PSC particles are thus a principal stratospheric characteristic related to gravity waves affecting particle evolution.
Journal of Atmospheric and Solar-terrestrial Physics, 2009
We present the first observational proof that polar mesospheric cloud (PMC) brightness responds to stratospheric gravity waves (GWs) differently at different latitudes by analyzing the Fe Boltzmann lidar data collected from the South Pole and Rothera (67.51S, 68.01W), Antarctica. Stratospheric GW strength is characterized by the root-mean-square (RMS) relative density perturbation in the 30-45 km region and PMC brightness is represented by the total backscatter coefficient (TBC) in austral summer from November to February. The linear correlation coefficient (LCC) between GW strength and PMC brightness is found to be +0.09 with a 42% confidence level at the South Pole and À0.49 with a 98% confidence level at Rothera. If a PMC case potentially affected by a space shuttle exhaust plume is removed from the Rothera dataset, the negative correlation coefficient and confidence level increase to À0.61 and 99%, respectively. The Rothera negative correlation increases when shorter-period waves are included while no change is observed in the South Pole correlation. Therefore, observations show statistically that Rothera PMC brightness is negatively correlated with the stratospheric GW strength but no significant correlation exists at the South Pole. A positive correlation of +0.74 with a confidence level of 99.98% is found within a distinct subset of the South Pole data but the rest of the dataset exhibits a random distribution, possibly indicating different populations of ice particles at the South Pole. Our data show that these two locations have similar GW strength and spectrum in the 30-45 km region during summer. The different responses of PMC brightness to GW perturbations are likely caused by the latitudinal differences in background temperatures in the ice crystal growth region between the PMC altitude and the mesopause. At Rothera, where temperatures in this region are relatively warm and supersaturations are not as large, GW-induced temperature perturbations can drive subsaturation in the warm phase. Thus, GWs can destroy growing ice crystals or limit their growth, leading to negative correlation at Rothera. Because the South Pole temperatures in the mesopause region are much colder, GW-perturbed temperature may never be above the frost point and have less of an impact on crystal growth and PMC brightness. The observed phenomena and proposed mechanisms above need to be understood and verified through future modeling of GW effects on PMC microphysics and ray modeling of GW propagation over the South Pole and Rothera.
Using the Modern Era Retrospective-Analysis for Research and Applications (MERRA) and MERRA-2 reanalysis winds, temperatures, and anvil cloud ice, we explore the impact of varying the cloud nucleation threshold relative humidity (RH) and high-frequency gravity waves on stratospheric water vapor (H 2 O) and upper tropical tropopause cloud fraction (TCF). Our model results are compared to 2008/2009 winter TCF derived from Cloud-Aerosol Lidar with Orthogonal Polarization and H 2 O observations from the Microwave Limb Sounder (MLS). The RH threshold affects both model H 2 O and TCF, while high-frequency gravity waves mostly impact TCF. Adjusting the nucleation RH and the amplitude of high-frequency gravity waves allows us to tune the model to observations. Reasonable observational agreement is obtained with a nucleation threshold between 130% and 150% RH consistent with airborne observations. For the MERRA reanalysis, we lower the tropopause temperature by 0.5 K roughly consistent with GPS radio occultation measurements and include~0.1 K high-frequency gravity wave temperature oscillations in order to match TCF and H 2 O observations. For MERRA-2 we do not need to adjust the tropopause temperature nor add gravity waves, because there are sufficient high-frequency temperature oscillations already present in the MERRA-2 reanalysis to reproduce the observed TCF.
Journal of Atmospheric and Solar-Terrestrial Physics, 2009
We present the first results of gravity wave signatures on polar mesospheric clouds (PMCs) during the summer of 2007, in the northern hemisphere polar region. The Cloud Imaging and Particle Size (CIPS) experiment has one of the three instruments on board the NASA Aeronomy of Ice in the Mesosphere (AIM) spacecraft, which was launched into a sun-synchronous orbit on April 25, 2007. CIPS is a fourcamera, wide-field (1201 Â 801) imager designed to measure PMC morphology and particle properties. One of the objectives of AIM is to investigate gravity wave effects on PMC formation and evolution. CIPS images show distinct wave patterns and structures in PMCs that are similar to ground-based photographs of noctilucent clouds (NLCs). The observed horizontal wavelengths of the waves were found to vary between 15 and 320 km, with smaller-wavelength structures of less than 50 km being the most common. In this paper we present examples of individual quasi-monochromatic wave events observed by CIPS and statistics on the wave patterns observed in the northern hemisphere during the summer months of 2007, together with a map showing the geographic locations of gravity wave events observed from CIPS.
Gravity waves in the middle atmosphere observed by Rayleigh lidar: 1. Case studies
Journal of Geophysical Research, 1991
Density and temperature mesoscale fluctuations as observed in the stratosphere and mesosphere by means of two Rayleigh lidars with high resolution in time (15 min) and space (300 m), have been analyzed in some particular cases corresponding to different seasonal conditions. These case studies are characteristic of recurrently observed patterns and thus provide a description of the mesoscale fluctuation field in the middle atmosphere. The spatial, temporal, and spectral characteristics of the fluctuations are described and discussed in the framework of the gravity wave interpretation. Dominant wave modes with large period and large vertical wavelength (inertia-gravity waves) are frequently observed in the stratosphere and lower mesosphere. These lowfrequency modes are not generally observed above 50-to 55km altitude, suggesting a strong damping of such waves in the mesosphere. The vertical growth of potential energy density indicates that the wave motions are generally not conservative in the middle atmosphere. The gravity waves amplitude appears too small to produce convective instabilities in the stratosphere. On the contrary, the amplitude of the fluctuations is close to the convective saturation limit deduced from the linear theory for wavelengths up to 3-5 km in the lower mesosphere, and up to 6-8 km above 60 km altitude. Furthermore, convectively instable layers, which can persist for periods longer than 1 hour, have been frequently observed in the mesosphere.