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- ItemHorizontal Wavenumber Spectra of Vertical Vorticity and Horizontal Divergence of Mesoscale Dynamics in the Mesosphere and Lower Thermosphere Using Multistatic Specular Meteor Radar Observations(Malden, Mass. : American Geophysical Union, 2022) Poblet, Facundo L.; Chau, Jorge L.; Conte, J. Federico; Avsarkisov, Victor; Vierinen, Juha; Charuvil Asokan, HarikrishnanSpecular meteor radars (SMRs) have significantly contributed to the understanding of wind dynamics in the mesosphere and lower thermosphere (MLT). We present a method to estimate horizontal correlations of vertical vorticity (Qzz) and horizontal divergence (P) in the MLT, using line-of-sight multistatic SMRs velocities, that consists of three steps. First, we estimate 2D, zonal, and meridional correlation functions of wind fluctuations (with periods less than 4 hr and vertical wavelengths smaller than 4 km) using the wind field correlation function inversion (WCFI) technique. Then, the WCFI's statistical estimates are converted into longitudinal and transverse components. The conversion relation is obtained by considering the rotation about the vertical direction of two velocity vectors, from an east-north-up system to a meteor-pair-dependent cylindrical system. Finally, following a procedure previously applied in the upper troposphere and lower stratosphere to airborne wind measurements, the longitudinal and transverse spatial correlations are fitted, from which Qzz, P, and their spectra are directly estimated. The method is applied to a special Spread spectrum Interferometric Multistatic meteor radar Observing Network data set, obtained over northern Germany for seven days in November 2018. The results show that in a quasi-axisymmetric scenario, P was more than five times larger than Qzz for the horizontal wavelengths range given by ∼50–400 km, indicating a predominance of internal gravity waves over vortical modes of motion as a possible explanation for the MLT mesoscale dynamics during this campaign.
- ItemMultistatic Specular Meteor Radar Network in Peru: System Description and Initial Results(Malden, Mass. : American Geophysical Union, 2021) Chau, J.L.; Urco, J.M.; Vierinen, J.; Harding, B.J.; Clahsen, M.; Pfeffer, N.; Kuyeng, K.M.; Milla, M.A.; Erickson, P.J.The mesosphere and lower thermosphere (MLT) region is dominated globally by dynamics at various scales: planetary waves, tides, gravity waves, and stratified turbulence. The latter two can coexist and be significant at horizontal scales less than 500 km, scales that are difficult to measure. This study presents a recently deployed multistatic specular meteor radar system, SIMONe Peru, which can be used to observe these scales. The radars are positioned at and around the Jicamarca Radio Observatory, which is located at the magnetic equator. Besides presenting preliminary results of typically reported large-scale features, like the dominant diurnal tide at low latitudes, we show results on selected days of spatially and temporally resolved winds obtained with two methods based on: (a) estimation of mean wind and their gradients (gradient method), and (b) an inverse theory with Tikhonov regularization (regularized wind field inversion method). The gradient method allows improved MLT vertical velocities and, for the first time, low-latitude wind field parameters such as horizontal divergence and relative vorticity. The regularized wind field inversion method allows the estimation of spatial structure within the observed area and has the potential to outperform the gradient method, in particular when more detections are available or when fine adaptive tuning of the regularization factor is done. SIMONe Peru adds important information at low latitudes to currently scarce MLT continuous observing capabilities. Results contribute to studies of the MLT dynamics at different scales inherently connected to lower atmospheric forcing and E-region dynamo related ionospheric variability.
- ItemObserving Mesospheric Turbulence with Specular Meteor Radars: a novel Method for Estimating Second-Order Statistics of Wind Velocity(Malden, Mass. : American Geophysical Union, 2019) Vierinen, J.; Chau, J.L.; Charuvil, H.; Urco, J.M.; Clahsen, M.; Avsarkisov, V.; Marino, R.; Volz, R.There are few observational techniques for measuring the distribution of kinetic energy within the mesosphere with a wide range of spatial and temporal scales. This study describes a method for estimating the three-dimensional mesospheric wind field correlation function from specular meteor trail echoes. Each radar echo provides a measurement of a one-dimensional projection of the wind velocity vector at a randomly sampled point in space and time. The method relies on using pairs of such measurements to estimate the correlation function of the wind with different spatial and temporal lags. The method is demonstrated using a multistatic meteor radar data set that includes ≈105 meteor echoes observed during a 24-hr time period. The new method is found to be in good agreement with the well-established technique for estimating horizontal mean winds. High-resolution correlation functions with temporal, horizontal, and vertical lags are also estimated from the data. The temporal correlation function is used to retrieve the kinetic energy spectrum, which includes the semidiurnal mode and a 3-hr period wave. The horizontal and vertical correlation functions of the wind are then used to derive second-order structure functions, which are found to be compatible with the Kolmogorov prediction for spectral distribution of kinetic energy in the turbulent inertial range. The presented method can be used to extend the capabilities of specular meteor radars. It is relatively flexible and has a multitude of applications beyond what has been shown in this study.
- ItemTen-year climatology of potassium number density at 54° N, 12° E(Amsterdam [u.a.] : Elsevier Science, 2017) Lautenbach, J.; Höffner, J.; Lübken, F.-J.; Kopp, M.; Gerding, M.In the years from 2002 to 2012 potassium densities observations were performed in the mesopause region at Kühlungsborn using a potassium Doppler lidar. The 10-year diurnal data set comprises 5090 h of potassium number densities at 741 days with 25.2% under full daylight conditions. Potassium number densities show a clear semi-annual variation with two broad maxima reoccurring every year. The first maximum occurs in summer and lasts for about 4 months (May–August) with number densities up to 60 atoms/cc. The second maximum is observed from early December to late February with densities up to 30 atoms/cc. Both the peak density and the column density are higher at solstices than at equinoxes. The large data set shows little variation of the mean layer over the 10 years.
- ItemMaking limb and nadir measurements comparable: A common volume study of PMC brightness observed by Odin OSIRIS and AIM CIPS(Amsterdam [u.a.] : Elsevier Science, 2017) Benze, Susanne; Gumbel, Jörg; Randall, Cora E.; Karlsson, Bodil; Hultgren, Kristoffer; Lumpe, Jerry D.; Baumgarten, GerdCombining limb and nadir satellite observations of Polar Mesospheric Clouds (PMCs) has long been recognized as problematic due to differences in observation geometry, scattering conditions, and retrieval approaches. This study offers a method of comparing PMC brightness observations from the nadir-viewing Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument and the limb-viewing Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). OSIRIS and CIPS measurements are made comparable by defining a common volume for overlapping OSIRIS and CIPS observations for two northern hemisphere (NH) PMC seasons: NH08 and NH09. We define a scattering intensity quantity that is suitable for either nadir or limb observations and for different scattering conditions. A known CIPS bias is applied, differences in instrument sensitivity are analyzed and taken into account, and effects of cloud inhomogeneity and common volume definition on the comparison are discussed. Not accounting for instrument sensitivity differences or inhomogeneities in the PMC field, the mean relative difference in cloud brightness (CIPS - OSIRIS) is −102 ± 55%. The differences are largest for coincidences with very inhomogeneous clouds that are dominated by pixels that CIPS reports as non-cloud points. Removing these coincidences, the mean relative difference in cloud brightness reduces to −6 ± 14%. The correlation coefficient between the CIPS and OSIRIS measurements of PMC brightness variations in space and time is remarkably high, at 0.94. Overall, the comparison shows excellent agreement despite different retrieval approaches and observation geometries.
- ItemLong term trends of mesopheric ice layers: A model study(Amsterdam [u.a.] : Elsevier Science, 2021) Lübken, Franz-Josef; Baumgarten, Gerd; Berger, UweTrends derived from the Leibniz-Institute Middle Atmosphere Model (LIMA) and the MIMAS ice particle model (Mesospheric Ice Microphysics And tranSport model) are presented for a period of 138 years (1871–2008) and for middle, high, and arctic latitudes, namely 58°N, 69°N, and 78°N, respectively. We focus on the analysis of mesospheric ice layers (NLC, noctilucent clouds) in the main summer season (July) and on yearly mean values. Model runs with and without an increase of carbon dioxide and water vapor (from methane oxidation) concentrations are performed. Trends are most prominent after ~1960 when the increase of both CO2 and H2O accelerates. It is important to distinguish between tendencies on geometric altitudes and on given pressure levels converted to altitudes (‘pressure altitudes’). Negative trends of (geometric) NLC altitudes are primarily due to cooling below NLC altitudes caused by CO2 increase. Increases of ice particle radii and NLC brightness with time are mainly caused by an enhancement of water vapor. Several ice layer and background parameter trends are similar at high and arctic latitudes but are substantially different at middle latitudes. This concerns, for example, occurrence rates, ice water content (IWC), and number of ice particles in a column. Considering the time period after 1960, geometric altitudes of NLC decrease by approximately 260 m per decade, and brightness increases by roughly 50% (1960–2008), independent of latitude. NLC altitudes decrease by approximately 15–20 m per increase of CO2 by 1 ppmv. The number of ice particles in a column and also at the altitude of maximum backscatter is nearly constant with time. At all latitudes, yearly mean NLC appear at altitudes where temperatures are close to 145±1 K. Ice particles are present nearly all the time at high and arctic latitudes, but are much less common at middle latitudes. Ice water content and maximum backscatter (βmax) are highly correlated, where the slope depends on latitude. This allows to combine data sets from satellites and lidars. Furthermore, IWC and the concentration of water vapor at βmax are also strongly correlated. Nearly all trends depend on a lower limit applied for βmax, e.g., IWC and occurrence rates. Results from LIMA/MIMAS are in very good agreement with observations.
- ItemImpacts of a sudden stratospheric warming on the mesospheric metal layers(Amsterdam [u.a.] : Elsevier Science, 2017) Feng, Wuhu; Kaifler, Bernd; Marsh, Daniel R.; Höffner, Josef; Hoppe, Ulf-Peter; Williams, Bifford P.; Plane, John M.C.We report measurements of atomic sodium, iron and temperature in the mesosphere and lower thermosphere (MLT) made by ground-based lidars at the ALOMAR observatory (69°N, 16°E) during a major sudden stratospheric warming (SSW) event that occurred in January 2009. The high resolution temporal observations allow the responses of the Na and Fe layers to the SSW at high northern latitudes to be investigated. A significant cooling with temperatures as low as 136 K around 90 km was observed on 22–23 January 2009, along with substantial depletions of the Na and Fe layers (an ~80% decrease in the column abundance with respect to the mean over the observation period). The Whole Atmosphere Community Climate Model (WACCM) incorporating the chemistry of Na, Fe, Mg and K, and nudged with reanalysis data below 60 km, captures well the timing of the SSW, although the extent of the cooling and consequently the depletion in the Na and Fe layers is slightly underestimated. The model also predicts that the perturbations to the metal layers would have been observable even at equatorial latitudes. The modelled Mg layer responds in a very similar way to Na and Fe, whereas the K layer is barely affected by the SSW because of the enhanced conversion of K+ ions to K atoms at the very low temperatures.
- ItemLidar Soundings Between 30 and 100 km Altitude During Day and Night for Observation of Temperatures, Gravity Waves and Tides(Les Ulis : EDP Sciences, 2016) Gerding, Michael; Baumgarten, Kathrin; Höffner, Josef; Lübken, Franz-Josef; Gross, Barry; Moshary, F.; Arend, M.Ground-based temperature measurements by lidar are an important tool for the understanding of long-term temperature changes as well as the propagation of gravity waves and tides. Though, mesospheric soundings are often limited to nighttime conditions due to the low signal-tonoise ratio during the day. We developed a daylight-capable RMR lidar for temperature soundings in the middle atmosphere. The influences of the narrowband detector on the calculated hydrostatic temperatures as well as their correction are described. The RMR lidar is complemented by a co-located resonance lidar. We present an example for tidal analyses and short-term variability of tidal amplitudes