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- ItemOn statistics of the free-troposphere synoptic component: An evaluation of skewnesses and mixed third-order moments contribution to the synoptic-scale dynamics and fluxes of heat and humidity(Abingdon : Taylor and Francis Ltd., 2008) Petoukhov, V.; Eliseev, A.V.; Klein, R.; Oesterle, H.Based on the ERA40 data for 1976-2002 we calculated skewnesses and mixed third-order statistical moments (TOMs) for the synoptic variations [with (2.5-6) d timescales]of horizontal winds, temperature, vertical velocity and the specific humidity in Eulerian coordinates. All these variables show skewnesses which markedly deviate from zero, basically at the entries and the outlets of the mid-latitude storm tracks. In these regions, high values of skewness for vertical velocity, temperature and the specific humidity are revealed throughout the entire free troposphere, while the marked skewnesses for horizontal winds are traced in the lower free troposphere. We found a notable deviation of the synoptic-component statistics from the Gaussian statistics. We also made an estimate of the contribution from TOMs to the prognostic equations for the synoptic-scale kinetic energy and the meridional fluxes of sensible and latent heat, which appeared to be non-negligible, mainly in the storm tracks in winter. Our analysis attests that the most pronounced contribution of TOMs to the aforementioned equations comes from the self-advection by the horizontal synoptic-scale motions, while the TOMs induced by the metric terms in the original equations, and specifically the TOMs associated with the vertical self-advection by the synoptic-scale motions, are much less important.
- ItemMALTE - Model to predict new aerosol formation in the lower troposphere(München : European Geopyhsical Union, 2006) Boy, M.; Hellmuth, O.; Korhonen, H.; Nilsson, E.D.; ReVelle, D.; Turnipseed, A.; Arnold, F.; Kulmala, M.The manuscript presents a detailed description of the meteorological and chemical code of Malte – a model to predict new aerosol formation in the lower troposphere. The aerosol dynamics are achieved by the new developed UHMA (University of Helsinki Multicomponent Aerosol Model) code with kinetic limited nucleation as responsible mechanism to form new clusters. First results indicate that the model is able to predict the on- and offset of new particle formation as well as the total aerosol number concentrations that were in good agreement with the observations. Further, comparison of predicted and measured H2SO4 concentrations showed a satisfactory agreement. The simulation results indicated that at a certain transitional particle diameter (2–7 nm), organic molecules can begin to contribute significantly to the growth rate compared to sulphuric acid. At even larger particle sizes, organic molecules can dominate the growth rate on days with significant monoterpene concentrations. The intraday vertical evolution of newly formed clusters and particles in two different size ranges resulted in two maxima at the ground. These particles grow around noon to the detectable size range and agree well with measured vertical profiles.
- ItemSeasonal variation of nocturnal temperatures between 1 and 105 km altitude at 54° N observed by lidar(München : European Geopyhsical Union, 2008) Gerding, M.; Höffner, J.; Lautenbach, J.; Rauthe, M.; Lübken, F.-J.Temperature soundings are performed by lidar at the mid-latitude station of Kühlungsborn (Germany, 54° N, 12° E). The profiles cover the complete range from the lower troposphere (~1 km) to the lower thermosphere (~105 km) by simultaneous and co-located operation of a Rayleigh-Mie-Raman lidar and a potassium resonance lidar. Observations have been done during 266 nights between June 2002 and July 2007, each of 3–15 h length. This large and unique data set provides comprehensive information on the altitudinal and seasonal variation of temperatures from the troposphere to the lower thermosphere. The remaining day-to-day-variability is strongly reduced by harmonic fits at constant altitude levels and a representative data set is achieved. This data set reveals a two-level mesopause structure with an altitude of about 86–87 km (~144 K) in summer and ~102 km (~170 K) during the rest of the year. The average stratopause altitude is ~48 km throughout the whole year, with temperatures varying between 258 and 276 K. From the fit parameters amplitudes and phases of annual, semi-annual, and quarter-annual variations are derived. The amplitude of the annual component is largest with amplitudes of up to 30 K in 85 km, while the quarter-annual variation is smallest and less than 3 K at all altitudes. The lidar data set is compared with ECMWF temperatures below about 70 km altitude and reference data from the NRLMSISE-00 model above. Apart from the temperature soundings the aerosol backscatter ratio is measured between 20 and 35 km. The seasonal variation of these values is presented here for the first time.
- ItemLongitude-dependent decadal ozone changes and ozone trends in boreal winter months during 1960-2000(Göttingen : Copernicus, 2008) Peters, D.H.W.; Gabriel, A.; Entzian, G.This study examines the longitude-dependent decadal changes and trends of ozone for the boreal winter months during the period of 1960–2000. These changes are caused primarily by changes in the planetary wave structure in the upper troposphere and lower stratosphere. The decadal changes and trends over 4 decades of geopotential perturbations, defined as a deviation from the zonal mean, are estimated by linear regression with time. The decadal changes in longitude-dependent ozone were calculated with a simple transport model of ozone based on the known planetary wave structure changes and prescribed zonal mean ozone gradients. For December of the 1960s and 1980s a statistically significant Rossby wave track appeared over the North Atlantic and Europe with an anticyclonic disturbance over the Eastern North Atlantic and Western Europe, flanked by cyclonic disturbances. In the 1970s and 1990s statistically significant cyclonic disturbances appeared over the Eastern North Atlantic and Europe, surrounded by anticyclonic anomalies over Northern Africa, Central Asia and Greenland. Similar patterns have been found for January. The Rossby wave track over the North Atlantic and Europe is stronger in the 1980s than in the 1960s. For February, the variability of the regression patterns is higher. For January we found a strong alteration in the modelled decadal changes in total ozone over Central and Northern Europe, showing a decrease of about 15 DU in the 1960s and 1980s and an increase of about 10 DU in the 1970s and 1990s. Over Central Europe the positive geopotential height trend (increase of 2.3 m/yr) over 40 years is of the same order (about 100 m) as the increase in the 1980s alone. This is important to recognize because it implies a total ozone decrease over Europe of the order of 14 DU for the 1960–2000 period, for January, if we use the standard change regression relation that about a 10-m geopotential height increase at 300 hPa is related to about a 1.4-DU total ozone decrease.
- ItemValidation of the Atmospheric Chemistry Experiment (ACE) version 2.2 temperature using ground-based and space-borne measurements(München : European Geopyhsical Union, 2008) Sica, R.J.; Izawa, M.R.M.; Walker, K.A.; Boone, C.; Petelina, S.V.; Argall, P.S.; Bernath, P.; Burns, G.B.; Catoire, V.; Collins, R.L.; Daffer, W.H.; De Clercq, C.; Fan, Z.Y.; Firanski, B.J.; French, W.J.R.; Gerard, P.; Gerding, M.; Granville, J.; Innis, J.L.; Keckhut, P.; Kerzenmacher, T.; Klekociuk, A.R.; Kyrö, E.; Lambert, J.C.; Llewellyn, E.J.; Manney, G.L.; McDermid, I.S.; Mizutani, K.; Murayama, Y.; Piccolo, C.; Raspollini, P.; Ridolfi, M.; Robert, C.; Steinbrecht, W.; Strawbridge, K.B.; Strong, K.; Stübi, R.; Thurairajah, B.An ensemble of space-borne and ground-based instruments has been used to evaluate the quality of the version 2.2 temperature retrievals from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The agreement of ACE-FTS temperatures with other sensors is typically better than 2 K in the stratosphere and upper troposphere and 5 K in the lower mesosphere. There is evidence of a systematic high bias (roughly 3–6 K) in the ACE-FTS temperatures in the mesosphere, and a possible systematic low bias (roughly 2 K) in ACE-FTS temperatures near 23 km. Some ACE-FTS temperature profiles exhibit unphysical oscillations, a problem fixed in preliminary comparisons with temperatures derived using the next version of the ACE-FTS retrieval software. Though these relatively large oscillations in temperature can be on the order of 10 K in the mesosphere, retrieved volume mixing ratio profiles typically vary by less than a percent or so. Statistical comparisons suggest these oscillations occur in about 10% of the retrieved profiles. Analysis from a set of coincident lidar measurements suggests that the random error in ACE-FTS version 2.2 temperatures has a lower limit of about ±2 K.
- ItemSpectral actinic flux in the lower troposphere: Measurement and 1-D simulations for cloudless, broken cloud and overcast situations(München : European Geopyhsical Union, 2005) Kylling, A.; Webb, A.R.; Kift, R.; Gobbi, G.P.; Ammannato, L.; Barnaba, F.; Bais, A.; Kazadzis, S.; Wendisch, M.; Jäkel, E.; Schmidt, S.; Kniffka, A.; Thiel, S.; Junkermann, W.; Blumthaler, M.; Silbernagl, R.; Schallhart, B.; Schmitt, R.; Kjeldstad, B.; Thorseth, T.M.; Scheirer, R.; Mayer, B.In September 2002, the first INSPECTRO campaign to study the influence of clouds on the spectral actinic flux in the lower troposphere was carried out in East Anglia, England. Measurements of the actinic flux, the irradiance and aerosol and cloud properties were made from four ground stations and by aircraft. The radiation measurements were modelled using the uvspec model and ancillary data. For cloudless conditions, the measurements of the actinic flux were reproduced by 1-D radiative transfer modelling within the measurement and model uncertainties of about ±10%. For overcast days, the ground-based and aircraft radiation measurements and the cloud microphysical property measurements are consistent within the framework of 1-D radiative transfer and within experimental uncertainties. Furthermore, the actinic flux is increased by between 60-100% above the cloud when compared to a cloudless sky, with the largest increase for the optically thickest cloud. Correspondingly, the below cloud actinic flux is decreased by about 55-65%. Just below the cloud top, the downwelling actinic flux has a maximum that is seen in both the measurements and the model results. For broken clouds the traditional cloud fraction approximation is not able to simultaneously reproduce the measured above-cloud enhancement and below-cloud reduction in the actinic flux.