Peter Spichtinger

Ice supersaturation in the tropopause region over Lindenberg, Germany

The occurrence of ice-supersaturation layers (in either clear air or in cirrus) over the Meteorological Observatory Lindenberg is investigated for the period February 2000 to April 2001 by means of the humidity, temperature, and pressure reports obtained from the Lindenberg corrected RS80A routine radiosonde. The RS80A routine sonde data are corrected on the basis of weekly comparison ascents with Lindenberg research radiosonde humidity data. This research sonde applies the Lindenberg measuring and evaluation technique of standardized frequencies. We study the frequency of occurrence of ice supersaturation in the tropopause region over Lindenberg, the vertical distribution of ice-supersaturation layers in the upper troposphere and lowermost stratosphere, their situation relative to the tropopause, their vertical dimensions, their temperatures and the statistical distribution of relative humidities. The mean frequency of occurrence of ice-supersaturation layers is about 28%. Most of them occur within a broad layer extending 200 hPa down from the tropopause. Most events occur in cold air with temperature below -40°C. Their vertical extensions can be fitted by a pair of Weibull distributions with mean 560 ± 610 m. The results are compared with findings from the MOZAIC project, from the SAGE II satellite instrument, and with various results from Lidar measurements.

Cirrus cloud formation and ice supersaturated regions in a global climate model

At temperatures below 238 K, cirrus clouds can form by homogeneous and heterogeneous ice nucleation mechanisms. ECHAM5 contains a two-moment cloud microphysics scheme and permits cirrus formation by homogeneous freezing of solution droplets and heterogeneous freezing on immersed dust nuclei. On changing the mass accommodation coefficient, α, of water vapor on ice crystals from 0.5 in the standard ECHAM5 simulation to 0.006 as suggested by previous laboratory experiments, the number of ice crystals increases by a factor of 14, as a result of the delayed relaxation of supersaturation. At the same time, the ice water path increases by only 29% in the global annual mean, indicating that the ice crystals are much smaller in the case of low α. As a consequence, the short wave and long wave cloud forcing at the top of the atmosphere increase by 15 and 18 W m−2, respectively. Assuming heterogeneous freezing caused by immersed dust particles instead of homogeneous freezing, the effect is much weaker, decreasing the global annual mean short wave and long wave cloud forcing by 2.7 and 4.7 W m−2. Overall, these results provide little support, if any, for kinetic growth limitation of ice particles (i.e. a very low α).

Impact of ice supersaturated regions and thin cirrus on radiation in the midlatitudes

[1] In this study we investigate the radiative impact of ice supersaturated regions (ISSRs, i.e., cloud free air masses in the upper troposphere that are supersaturated with respect to ice) and thin cirrus. For this purpose we use corrected radiosonde data obtained from routine measurements over the meteorological observatory in Lindenberg, Germany. The radiative effect of the measured ice supersaturation is determined. By constructing an idealized profile from the measurement data the radiative properties of ISSRs and thin cirrus containing ice supersaturation were studied. The impact of ISSRs on the surface forcing is negligible but locally, within the vertical profile, changes in the heating rates up to 1 K d -1 for typical values of 130% relative humidity with respect to ice compared to the saturated profiles are found. This is also important for the local dynamics within the supersaturated layers. The outgoing longwave radiation due to the enhanced water vapor content inside ISSRs decreases up to 0.8 W m -2 . The radiative impact of thin cirrus is much stronger. Thin cirrus influence the surface budget, the top of the atmosphere radiation and the vertical profile of the heating rates. Changes in the outgoing longwave radiation and in the reflected shortwave flux at top of the atmosphere up to 64 W m -2 and 79 W m -2 , respectively, are possible. Changes in the surface flux (downward) up to 89 W m -2 are found. The maximal heating rate differences between thin cirrus and ISSR amount to 15 K d -1 . The radiative impact of thin cirrus clouds depends strongly on cloud ice content and the size of the ice crystals. Additionally, the radiative impact of cirrus formed by parameterizations not allowing ice supersaturations in large-scale models is estimated. The errors due to artificially formed cirrus are quite large; differences up to 3 K d -1 in the vertical heating profiles and up to 38 and 40 W m -2 in the outgoing longwave radiation and the surface flux, respectively, are found. Thus we recommend using physically based parameterizations in GCMs which allow ice supersaturation.

ML-CIRRUS - The airborne experiment on natural cirrus and contrail cirrus with the high-altitude long-range research aircraft HALO

AbstractThe Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 f...

The evolution of contrail microphysics in the vortex phase

We investigate the evolution of contrails during the vortex phase using numerical simulations. Emphasis is placed on microphysical properties and on the vertical distribution of ice mass and number concentration at the end of the vortex phase. Instead of using a 3D model which would be preferable but computationally too costly, we use a 2D model equipped with a special tool for controlling vortex decay. We conduct a great number of sensitivity studies for one aircraft type. It turns out that atmospheric parameters, namely supersaturation, temperature, stability and turbulence level have the biggest impact on the number of ice crystals and on the ice mass that survives until vortex breakup and that therefore makes up the persistent contrail in supersaturated air. The initial ice crystal number density and its distribution in the vortex, are of minor importance.

The Statistical Distribution Law of Relative Humidity in the Global Tropopause Region

Cloud cleared Microwave Limb Sounder (MLS) data of upper tropospheric humidity are evaluated in order to determine the global statistics of relative humidity with respect to ice, RHi. The evaluation is performed for the 215 hPa level, in order to compare the results with earlier results from the Measurement of ozone by Airbus in-service aircraft (MOZAIC) project. In agreement with the earlier study we find that in the lowermost stratosphere the probability to get a certain value of relative humidity decreases exponentially with the relative humidity. In the Antarctic data class (data south of 55°S, mainly winter data) we also find an exponential distribution for RHi but with less steep slope. There is no change in the slope of the exponential distribution function at ice saturation. In the upper troposphere there are corresponding exponential distributions for RHi in ice-supersaturated regions and in subsaturated regions (for 20% 150%, and the exponential distributions extend without change of slope up to 180-200%. Such extreme humidity events occur mostly in the tropics and at the edge of Antarctica, and could result from incidental lack of aerosol.

Application and Comparison of Robust Linear Regression Methods for Trend Estimation

In this study, robust parametric regression methods are applied to temperature and precipitation time series in Switzerland and the trend results are compared with trends from classical least squares (LS) regression and nonparametric approaches. It is found that in individual time series statistically outlying observations are present that influence the LS trend estimate severely. In some cases, these outlying observations lead to an over-/underestimation of the trends or even to a trend masking. In comparison with the classical LS method and standard nonparametric techniques, the use of robust methods yields more reliable trend estimations and outlier detection.

A trajectory-based classification of ERA-Interim ice clouds in the region of the North Atlantic storm track

A two-type classification of ice clouds (cirrus) is introduced, based on the liquid and ice water content, LWC and IWC, along air parcel backward trajectories from the clouds. In situ cirrus has no LWC along the trajectory segment containing IWC; it forms via nucleation from the gas phase. In contrast, liquid-origin cirrus has both LWC and IWC along their backward trajectories; it forms via lifting from the lower troposphere and freezing of mixed-phase clouds. This classification is applied to 12 years of ERA-Interim ice clouds in the North Atlantic region. Between 400 and 500 hPa more than 50% are liquid-origin cirrus, whereas this frequency decreases strongly with altitude (<10% at 200 hPa). The relative frequencies of the two categories vary only weakly with season. More than 50% of in situ cirrus occur on top of liquid-origin cirrus, indicating that they often form in response to the strong lifting accompanying the formation of liquid-origin cirrus.

Aerosol?cloud interactions?a challenge for measurements and modeling at the cutting edge of cloud?climate interactions

Research in aerosol properties and cloud characteristics have historically been considered two separate disciplines within the field of atmospheric science. As such, it has been uncommon for a single researcher, or even research group, to have considerable expertise in both subject areas. The recent attention paid to global climate change has shown that clouds can have a considerable effect on the Earths climate and that one of the most uncertain aspects in their formation, persistence, and ultimate dissipation is the role played by aerosols. This highlights the need for researchers in both disciplines to interact more closely than they have in the past. This is the vision behind this focus issue of Environmental Research Letters. Certain interactions between aerosols and clouds are relatively well studied and understood. For example, it is known that an increase in the aerosol concentration will increase the number of droplets in warm clouds, decrease their average size, reduce the rate of precipitation, and extend the lifetime. Other effects are not as well known. For example, persistent ice super-saturated conditions are observed in the upper troposphere that appear to exceed our understanding of the conditions required for cirrus cloud formation. Further, the interplay of dynamics versus effects purely attributed to aerosols remains highly uncertain. The purpose of this focus issue is to consider the current state of knowledge of aerosol/cloud interactions, to define the contemporary uncertainties, and to outline research foci as we strive to better understand the Earths climate system. This focus issue brings together laboratory experiments, field data, and model studies. The authors address issues associated with warm liquid water, cold ice, and intermediate temperature mixed-phase clouds. The topics include the uncertainty associated with the effect of black carbon and organics, aerosol types of anthropogenic interest, on droplet and ice formation. Phases of water which have not yet been fully defined, for example cubic ice, are considered. The impact of natural aerosols on clouds, for example mineral dust, is also discussed, as well as other natural but highly sensitive effects such as the Wegener?Bergeron?Findeisen process. It is our belief that this focus issue represents a leap forward not only in reducing the uncertainty associated with the interaction of aerosols and clouds but also a new link between groups that must work together to continue progress in this important area of climate science. Focus on Aerosol?Cloud Interactions Contents The global influence of dust mineralogical composition on heterogeneous ice nucleation in mixed-phase clouds C Hoose, U Lohmann, R Erdin and I Tegen Ice formation via deposition nucleation on mineral dust and organics: dependence of onset relative humidity on total particulate surface area Zamin A Kanji, Octavian Florea and Jonathan P D Abbatt The Explicit-Cloud Parameterized-Pollutant hybrid approach for aerosol?cloud interactions in multiscale modeling framework models: tracer transport results William I Gustafson Jr, Larry K Berg, Richard C Easter and Steven J Ghan Cloud effects from boreal forest fire smoke: evidence for ice nucleation from polarization lidar data and cloud model simulations Kenneth Sassen and Vitaly I Khvorostyanov The effect of organic coating on the heterogeneous ice nucleation efficiency of mineral dust aerosols O M?hler, S Benz, H Saathoff, M Schnaiter, R Wagner, J Schneider, S Walter, V Ebert and S Wagner Enhanced formation of cubic ice in aqueous organic acid droplets Benjamin J Murray Quantification of water uptake by soot particles O B Popovicheva, N M Persiantseva, V Tishkova, N K Shonija and N A Zubareva Meridional gradients of light absorbing carbon over northern Europe D Baumgardner, G Kok, M Kr?mer and F Weidle MAID: a model to simulate UT/LS aerosols and ice clouds H Bunz, S Benz, I Gensch and M Kr?mer Single-parameter estimates of aerosol water content S M Kreidenweis, M D Petters and P J DeMott Supersaturations, microphysics and nitric acid partitioning in a cold cirrus cloud observed during CR-AVE 2006: an observation?modelling intercomparison study I V Gensch, H Bunz, D G Baumgardner, L E Christensen, D W Fahey, R L Herman, P J Popp, J B Smith, R F Troy, C R Webster, E M Weinstock, J C Wilson, T Peter and M Kr?mer Connecting hygroscopic growth at high humidities to cloud activation for different particle types H Wex, F Stratmann, T Hennig, S Hartmann, D Niedermeier, E Nilsson, R Ocskay, D Rose, I Salma and M Ziese Modeling of the Wegener?Bergeron?Findeisen process?implications for aerosol indirect effects T Storelvmo, J E Kristj?nsson, U Lohmann, T Iversen, A Kirkev?g and ? Seland Droplet nuclei in non-precipitating clouds: composition and size matter Cynthia H Twohy and James R Anderson A laboratory investigation of the relative humidity dependence of light extinction by organic compounds from lignin combustion Melinda R Beaver, Rebecca M Garland, Christa A Hasenkopf, Tahllee Baynard, A R Ravishankara and Margaret A Tolbert Cirrus cloud formation and ice supersaturated regions in a global climate model Ulrike Lohmann, Peter Spichtinger, Stephanie Jess, Thomas Peter and Herman Smit Notes on state-of-the-art investigations of aerosol effects on precipitation: a critical review A P Khain

Improvement and Implementation of a Parameterization for Shallow Cumulus in the Global Climate Model ECHAM5-HAM

Abstract A transient shallow-convection scheme is implemented into the general circulation model ECHAM5 and the coupled aerosol model HAM, developed at the Max Planck Institute for Meteorology in Hamburg. The shallow-convection scheme is extended to take the ice phase into account. In addition, a detailed double-moment microphysics approach has been added. In this approach, the freezing processes and precipitation formation are dependent on aerosols. Furthermore, in the scheme, tracers are transported and scavenged consistently as in the rest of the model. Results of a single-column model simulation for the Barbados Oceanography and Meteorology Experiment (BOMEX) campaign are compared with previously published large-eddy simulation (LES) results. Compared to the standard version, the global ECHAM5-HAM simulations with the newly implemented scheme show a decreased frequency of shallow convection in better agreement with LES. Less shallow convection is compensated by more stratus and stratocumulus. Deep and...