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- ItemDual-FOV Raman and Doppler lidar studies of aerosol-cloud interactions: Simultaneous profiling of aerosols, warm-cloud properties, and vertical wind(Hoboken, NJ : Wiley, 2014) Schmidt, Jörg; Ansmann, Albert; Bühl, Johannes; Baars, Holger; Wandinger, Ulla; Müller, Detlef; Malinka, Aleksey V.For the first time, colocated dual-field of view (dual-FOV) Raman lidar and Doppler lidar observations (case studies) of aerosol and cloud optical and microphysical properties below and within thin layered liquid water clouds are presented together with an updraft and downdraft characterization at cloud base. The goal of this work is to investigate the relationship between aerosol load close to cloud base and cloud characteristics of warm (purely liquid) clouds and the study of the influence of vertical motions and turbulent mixing on this relationship. We further use this opportunity to illustrate the applicability of the novel dual-FOV Raman lidar in this field of research. The dual-FOV lidar combines the well-established multiwavelength Raman lidar technique for aerosol retrievals and the multiple-scattering Raman lidar technique for profiling of the single-scattering extinction coefficient, effective radius, number concentration of the cloud droplets, and liquid water content. Key findings of our 3 year observations are presented in several case studies of optically thin altocumulus layers occurring in the lower free troposphere between 2.5 and 4 km height over Leipzig, Germany, during clean and polluted situations. For the clouds that we observed, the most direct link between aerosol proxy (particle extinction coefficient) and cloud proxy (cloud droplet number concentration) was found at cloud base during updraft periods. Above cloud base, additional processes resulting from turbulent mixing and entrainment of dry air make it difficult to determine the direct impact of aerosols on cloud processes.
- ItemA global atmospheric model of meteoric iron(Hoboken, NJ : Wiley, 2013) Feng, Wuhu; Marsh, Daniel R.; Chipperfield, Martyn P.; Janches, Diego; Höffner, Josef; Yi, Fan; Plane, John M.C.The first global model of meteoric iron in the atmosphere (WACCM-Fe) has been developed by combining three components: the Whole Atmosphere Community Climate Model (WACCM), a description of the neutral and ion-molecule chemistry of iron in the mesosphere and lower thermosphere (MLT), and a treatment of the injection of meteoric constituents into the atmosphere. The iron chemistry treats seven neutral and four ionized iron containing species with 30 neutral and ion-molecule reactions. The meteoric input function (MIF), which describes the injection of Fe as a function of height, latitude, and day, is precalculated from an astronomical model coupled to a chemical meteoric ablation model (CABMOD). This newly developed WACCM-Fe model has been evaluated against a number of available ground-based lidar observations and performs well in simulating the mesospheric atomic Fe layer. The model reproduces the strong positive correlation of temperature and Fe density around the Fe layer peak and the large anticorrelation around 100 km. The diurnal tide has a significant effect in the middle of the layer, and the model also captures well the observed seasonal variations. However, the model overestimates the peak Fe+concentration compared with the limited rocket-borne mass spectrometer data available, although good agreement on the ion layer underside can be obtained by adjusting the rate coefficients for dissociative recombination of Fe-molecular ions with electrons. Sensitivity experiments with the same chemistry in a 1-D model are used to highlight significant remaining uncertainties in reaction rate coefficients, and to explore the dependence of the total Fe abundance on the MIF and rate of vertical transport.
- ItemCauses and importance of new particle formation in the present-day and preindustrial atmospheres(Hoboken, NJ : Wiley, 2017) Gordon, Hamish; Kirkby, Jasper; Baltensperger, Urs; Bianchi, Federico; Breitenlechner, Martin; Curtius, Joachim; Dias, Antonio; Dommen, Josef; Donahue, Neil M.; Dunne, Eimear M.; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C.; Frege, Carla; Fuchs, Claudia; Hansel, Armin; Hoyle, Christopher R.; Kulmala, Markku; Kürten, Andreas; Lehtipalo, Katrianne; Makhmutov, Vladimir; Molteni, Ugo; Rissanen, Matti P.; Stozkhov, Yuri; Tröstl, Jasmin; Tsagkogeorgas, Georgios; Wagner, Robert; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M.; Yan, Chao; Carslaw, Ken S.New particle formation has been estimated to produce around half of cloud-forming particles in the present-day atmosphere, via gas-to-particle conversion. Here we assess the importance of new particle formation (NPF) for both the present-day and the preindustrial atmospheres. We use a global aerosol model with parametrizations of NPF from previously published CLOUD chamber experiments involving sulfuric acid, ammonia, organic molecules, and ions. We find that NPF produces around 67% of cloud condensation nuclei at 0.2% supersaturation (CCN0.2%) at the level of low clouds in the preindustrial atmosphere (estimated uncertainty range 45–84%) and 54% in the present day (estimated uncertainty range 38–66%). Concerning causes, we find that the importance of biogenic volatile organic compounds (BVOCs) in NPF and CCN formation is greater than previously thought. Removing BVOCs and hence all secondary organic aerosol from our model reduces low-cloud-level CCN concentrations at 0.2% supersaturation by 26% in the present-day atmosphere and 41% in the preindustrial. Around three quarters of this reduction is due to the tiny fraction of the oxidation products of BVOCs that have sufficiently low volatility to be involved in NPF and early growth. Furthermore, we estimate that 40% of preindustrial CCN0.2% are formed via ion-induced NPF, compared with 27% in the present day, although we caution that the ion-induced fraction of NPF involving BVOCs is poorly measured at present. Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions.
- ItemIce residual properties in mixed-phase clouds at the high-alpine Jungfraujoch site(Hoboken, NJ : Wiley, 2016) Kupiszewski, Piotr; Zanatta, Marco; Mertes, Stephan; Vochezer, Paul; Lloyd, Gary; Schneider, Johannes; Schenk, Ludwig; Schnaiter, Martin; Baltensperger, Urs; Weingartner, Ernest; Gysel, MartinIce residual (IR) and total aerosol properties were measured in mixed-phase clouds (MPCs) at the high-alpine Jungfraujoch research station. Black carbon (BC) content and coating thickness of BC-containing particles were determined using single-particle soot photometers. The ice activated fraction (IAF), derived from a comparison of IR and total aerosol particle size distributions, showed an enrichment of large particles in the IR, with an increase in the IAF from values on the order of 10−4 to 10−3 for 100 nm (diameter) particles to 0.2 to 0.3 for 1 μm (diameter) particles. Nonetheless, due to the high number fraction of submicrometer particles with respect to total particle number, IR size distributions were still dominated by the submicrometer aerosol. A comparison of simultaneously measured number size distributions of BC-free and BC-containing IR and total aerosol particles showed depletion of BC by number in the IR, suggesting that BC does not play a significant role in ice nucleation in MPCs at the Jungfraujoch. The potential anthropogenic climate impact of BC via the glaciation effect in MPCs is therefore likely to be negligible at this site and in environments with similar meteorological conditions and a similar aerosol population. The IAF of the BC-containing particles also increased with total particle size, in a similar manner as for the BC-free particles, but on a level 1 order of magnitude lower. Furthermore, BC-containing IR were found to have a thicker coating than the BC-containing total aerosol, suggesting the importance of atmospheric aging for ice nucleation.
- ItemRadiative effect of aerosols above the northern and southern Atlantic Ocean as determined from shipborne lidar observations(Hoboken, NJ : Wiley, 2013) Kanitz, T.; Ansmann, Albert; Seifert, P.; Engelmann, R.; Althausen, D.The direct solar radiative effect of aerosols over the Atlantic Ocean was investigated on the basis of aerosol Raman/polarization lidar observations aboard the research vessel Polarsternbetween Germany (50°N) and either South America (50°S) or South Africa (40°S) in 2009 and 2010. First, a case study of complex aerosol conditions with marine aerosol, dust, and smoke particles in the boundary layer and free troposphere is presented to demonstrate that detailed knowledge of aerosol layering (boundary layer, free troposphere) and aerosol mixing state is required for an accurate determination of the resulting radiative effects. A statistical analysis based on all lidar observations revealed the highest daily mean radiative effect (−43±59 W m−2at the surface, −14±18 W m−2at top of atmosphere) in the latitudinal belt from 0°N–15°N in the Saharan dust outflow region. Mean aerosol radiative effects of the polluted northern and clean southern midlatitudes were contrasted. In the northern midlatitudes, the averaged aerosol radiative effect of all simulations was −24±33 W m−2at the surface which is a factor of 1.6 higher than at similar southern hemispheric latitudes. The simulations based on the lidar observations are in good agreement with colocated pyranometer measurements.
- ItemSolar cycle response and long-term trends in the mesospheric metal layers(Hoboken, NJ : Wiley, 2016) Dawkins, E.C.M.; Plane, J.M.C.; Chipperfield, M.P.; Feng, W.; Marsh, D.R.; Höffner, J.; Janches, D.The meteoric metal layers (Na, Fe, and K)—which form as a result of the ablation of incoming meteors—act as unique tracers for chemical and dynamical processes that occur within the upper mesosphere/lower thermosphere region. In this work, we examine whether these metal layers are sensitive indicators of decadal long-term changes within the upper atmosphere. Output from a whole-atmosphere climate model is used to assess the response of the Na, K, and Fe layers across a 50 year period (1955–2005). At short timescales, the K layer has previously been shown to exhibit a very different seasonal behavior compared to the other metals. Here we show that this unusual behavior is also exhibited at longer timescales (both the ~11 year solar cycle and 50 year periods), where K displays a much more pronounced response to atmospheric temperature changes than either Na or Fe. The contrasting solar cycle behavior of the K and Na layers predicted by the model is confirmed using satellite and lidar observations for the period 2004–2013.
- ItemLidar 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(Hoboken, NJ : Wiley, 2018-8-6) Chu, Xinzhao; Zhao, Jian; Lu, Xian; Harvey, V. Lynn; Jones, R. Michael; Becker, Erich; Chen, Cao; Fong, Weichun; Yu, Zhibin; Roberts, Brendan R.; Dörnbrack, AndreasFive 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.
- ItemObservations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming(Hoboken, NJ : Wiley, 2018-12-11) Triplett, Colin C.; Li, Jintai; Collins, Richard L.; Lehmacher, Gerald A.; Barjatya, Aroh; Fritts, David C.; Strelnikov, Boris; Lübken, Franz‐Josef; Thurairajah, Brentha; Harvey, V. Lynn; Hampton, Donald L.; Varney, Roger H.Measurements of turbulence and waves were made as part of the Mesosphere-Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25–26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65°N, 147°W). Rocket-borne ionization gauge measurements revealed turbulence in the 70- to 88-km altitude region with energy dissipation rates between 0.1 and 24 mW/kg with an average value of 2.6 mW/kg. The eddy diffusion coefficient varied between 0.3 and 134 m2/s with an average value of 10 m2/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground-based lidar measurements characterized the ensemble of inertia-gravity waves and monochromatic gravity waves. The ensemble of inertia-gravity waves had a specific potential energy of 0.8 J/kg over the 40- to 50-km altitude region, one of the lowest values recorded at Chatanika. The turbulence measurements coincided with the overturning of a 2.5-hr monochromatic gravity wave in a depth of 3 km at 85 km. The energy dissipation rates were estimated to be 3 mW/kg for the ensemble of waves and 18 mW/kg for the monochromatic wave. The MTeX observations reveal low levels of turbulence associated with low levels of gravity wave activity. In the light of other Arctic observations and model studies, these observations suggest that there may be reduced turbulence during disturbed winters.
- ItemGlobal observations of 2 day wave coupling to the diurnal tide in a high‐altitude forecast‐assimilation system(Hoboken, NJ : Wiley, 2017-4-18) Lieberman, R.S.; Riggin, D.M.; Nguyen, V.; Palo, S.E.; Siskind, D.E.; Mitchell, N.J.; Stober, G.; Wilhelm, S.; Livesey, N.J.We examine wave components in a high-altitude forecast-assimilation system that arise from nonlinear interaction between the diurnal tide and the westward traveling quasi 2 day wave. The process yields a westward traveling “sum” wave with zonal wave number 4 and a period of 16 h, and an eastward traveling “difference” wave with zonal wave number 2 and a period of 2 days. While the eastward 2 day wave has been reported in satellite temperatures, the westward 16 h wave lies outside the Nyquist limits of resolution of twice daily local time satellite sampling. Hourly output from a high-altitude forecast-assimilation model is used to diagnose the nonlinear quadriad. A steady state primitive equation model forced by tide-2 day wave advection is used to intepret the nonlinear wave products. The westward 16 h wave maximizes in the midlatitude winter mesosphere and behaves like an inertia-gravity wave. The nonlinearly generated component of the eastward 2 day wave maximizes at high latitudes in the lower thermosphere, and only weakly penetrates to low latitudes. The 16 h and the eastward 2 day waves are of comparable amplitude and alias to the same apparent frequency when viewed from a satellite perspective.
- ItemView angle dependence of MODIS liquid water path retrievals in warm oceanic clouds(Hoboken, NJ : Wiley, 2014) Horváth, Ákos; Seethala, Chellappan; Deneke, HartwigWe investigated the view angle dependence of domain mean Moderate Resolution Imaging Spectroradiometer (MODIS) liquid water path (LWP) and that of corresponding cloud optical thickness, effective radius, and liquid cloud fraction as proxy for plane-parallel retrieval biases. Independent Advanced Microwave Scanning Radiometer–EOS LWP was used to corroborate that the observed variations with sun-view geometry were not severely affected by seasonal/latitudinal changes in cloud properties. Microwave retrievals showed generally small (<10%) cross-swath variations. The view angle (cross-swath) dependence of MODIS optical thickness was weaker in backscatter than forward scatter directions and transitioned from mild ∩ shape to stronger ∪ shape as heterogeneity, sun angle, or latitude increased. The 2.2 µm effective radius variations always had a ∪ shape, which became pronounced and asymmetric toward forward scatter in the most heterogeneous clouds and/or at the lowest sun. Cloud fraction had the strongest and always ∪-shaped view angle dependence. As a result, in-cloud MODIS cloud liquid water path (CLWP) showed surprisingly good view angle (cross-swath) consistency, usually comparable to that of microwave retrievals, due to cancelation between optical thickness and effective radius biases. Larger (20–40%) nadir-relative increases were observed in the most extreme heterogeneity and sun angle bins, that is, typically in the polar regions, which, however, constituted only 3–8% of retrievals. The good consistency of MODIS in-cloud CLWP was lost for gridbox mean LWP, which was dominated by the strong cloud fraction increase with view angle. More worryingly, MODIS LWP exhibited significant and systematic absolute increases with heterogeneity and sun angle that is not present in microwave LWP.