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The Automatic Contrail Tracking Algorithm (ACTA) -developed to automatically follow contrails as they age, drift and spread- enables the study of a large number of contrails and the evolution of contrail properties with time. In this paper we present a year's worth of tracked contrails, from August 2008 to July 2009 in order to derive statistically significant mean values. The tracking is performed using the 5 min rapid-scan mode of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board of the Meteosat Second Generation satellites (MSG). The detection is based on the high spatial resolution of the images provided by the Moderate Resolution Imaging Spectroradiometer on board of the Terra satellite (Terra/MODIS), where a Contrail Detection Algorithm (CDA) is applied. The results show the satellite-derived average lifetimes of contrails and contrail-cirrus along with the probability density function (PDF) of other geometric characteristics such as mean coverage, distribution and width. In combination with specifically developed algorithms (RRUMS and COCS, explained below) it is possible to derive the radiative forcing (RF), energy forcing (EF), optical thickness (τ), and altitude of the tracked contrails. Mean values here retrieved are: duration, 1 h; length, 130 km; width, 8 km; altitude, 11.7 km; optical thickness, 0.34. Radiative forcing and energy forcing are shown for land/water backgrounds in day/night situations.

Airborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm−3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m−3. The Falcon flew in ash clouds up to about 0.8 mg m−3 for a few minutes and in an ash cloud with approximately 0.2 mg m−3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m−3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240–1600) kg s−1. The volcano induced about 10 (2.5–50) Tg of distal ash mass and about 3 (0.6–23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.

A description of two camera models is given which can be applied to along-track scanning radiometer 2 conical scanner images to provide estimates of cloud-top height and amount. Results are shown of initial quantitative assessments of these camera models and the underlying stereo-matching system applied to cloud-free areas in two different mountainous areas. These results indicate that for cloud-free areas with a sufficiently large range of heights the biases are mostly less than 1 km with standard deviations in the range of 0.31-4.96 km. This is in accordance within the predicted range of 1-2 km from previous theoretical studies.

Meteosat-derived hourly solar direct normal irradiances are compared to high quality ground measurements. For validation purposes the region of the Arabian Peninsula is selected due to its high solar energy potential and due to the availability of accurate ground measurements of the beam irradiance. Hourly ground data for the complete year 2000 are evaluated by automated and visual quality checks. Eight of 12 measurement sites fulfil the quality requirements and can be used for the validation purposes. The relative mean bias error, averaged over all 8 sites, is 4.3% for all-sky conditions. The relative root mean square error, averaged over all sites, decreases from 36.1% for hourly values down to 8.1% for the yearly sum. With this accuracy the method may well be applied for solar energy resource assessments in comparable regions and for detailed solar power plant simulations. Analysing one year of data of the Arabian Peninsula results in a maximum direct normal insolation of about 2650 kW h/m 2 in the north-east near Tabouk, while the minima can be found in the Al Soodah mountains with approximately 1650 kW h/m 2 .

During its more than 12 years of existence, the AVHRR Processing scheme Over cLouds, Land and Ocean (APOLLO) has been modified and extended. The intention of this paper is to document the present state of APOLLO and to summarize the experiences gained. The scope of the processing scheme is reviewed and the actual state of the daytime and night-time algorithms are presented. The reason for the modifications are discussed. Validations of the modifications are made by comparisons with surface observations. They show agreement to - % of the cloud coverage in 70% of the , 90 000 single comparisons. A consistency check with the International Satellite Cloud Climatology Project (ISCCP) shows the influence of coarse sampling on the ISCCP DX data reliability. APOLLO is now a robust and versatile cloud analysis tool. It is presently used to establish a cloud climatology in Central Europe, based on processing of 15 years of daily Advanced Very High Resolution Radiometer (AVHRR) data.

[1] Aviation induced cirrus (AIC) cover is identified from mean diurnal cycles of cirrus cover and air traffic density in the North Atlantic flight corridor. Traffic data for this region show an aviation “fingerprint” with two maxima during morning eastbound and afternoon westbound traffic. The same aviation fingerprint is found in cirrus cover. Cycle differences between west and east domain parts allow separating between aviation and natural diurnal changes. Cirrus cover is derived from 8 years of Meteosat infrared data. Linear contrail cover is estimated from the same data. Background cirrus without aviation impact is estimated from cirrus observations over the South Atlantic and from numerical weather prediction forecast. The cirrus cover cycle is well approximated by linear response to traffic density with fitted delay times of 2.3–4.1 h, implying AIC cover of 1–2%, more than expected from recent models.

The influence of cirrus clouds on the radiation budget of the Earth depends on their optical properties and their global coverage. The monitoring of cirrus coverage with instruments aboard geostationary satellites enables the investigation of cirrus clouds at the global scale as well as the identification of their diurnal variation. For instance, the Spinning Enhanced Visible and Infrared Imager (SEVIRI) aboard the Meteosat Second Generation (MSG) satellites provides data with high temporal resolution of 15 min and a spatial resolution of 3 km × 3 km at the sub-satellite point. In addition, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the sun-synchronous platforms Terra and Aqua delivers at least one observation per day with a high spatial resolutions ranging from 250 m × 250 m to 1 km × 1 km. Since the infrared channels of the SEVIRI instrument are suitable for an observation which is independent from day-light, Krebs et al. (2007) developed a cirrus detection algorithm for SEVIRI (called MeCiDA), based solely on its thermal channels. Since MeCiDA was optimised for the area of Europe only, we present an improved version of the algorithm which allows application to the full Meteosat disc. Required changes include the consideration of the viewing angle dependency and of the sensitivity of the 9.7 μm channel to the ozone column. To this end, a correction is implemented that minimises the influence of the variability of the stratospheric ozone. The validation of the proposed improvements is carried out by using MeCiDA applied to MODIS data to address viewing angle-dependent cirrus detection and by additionally comparing it to the Cloud Optical Properties MOD06 cirrus product. The new MeCiDA version detects less cirrus than the original one for latitudes larger than 40° but almost the same amount elsewhere. MeCiDA's version for MODIS is more sensitive than that for SEVIRI with cirrus occurrences higher by 10%, and the new MeCiDA provides almost the same cirrus coverage (±0.1) as given by the Cloud Phase Optical Properties from MODIS for latitudes smaller than 50°. Finally, the influence of sub-pixel clouds on the SEVIRI cirrus detection has been examined: more than 60% of the undetected SEVIRI cirrus pixels have a cirrus coverage smaller than 0.5.

A new Rapid Retrieval of upwelling fluxes from MSG/SEVIRI (RRUMS) is presented. It has been developed to observe the top-of-atmosphere irradiances of small scale and rapidly changing features that are not sufficiently resolved by specific Earth radiation budget sensors. Our retrieval takes advantage of the spatial and temporal resolution of MSG/SEVIRI and provides outgoing longwave and reflected shortwave radiation only by means of a combination of SEVIRI channels. The longwave retrieval is based on a simple linear combination of brightness temperatures from the SEVIRI infrared channels. Two shortwave retrievals are presented and discussed: the first one based on a multilinear parameterisation and the second one based on a neural network. The neural network method is shown to be slightly more accurate and simpler to apply for the desired purpose. Both LW and SW algorithms have been validated by comparing their results with CERES and GERB irradiance observations. While being less accurate than their dedicated counterparts, the SEVIRI-based methods have two major advantages compared to CERES and GERB: their higher spatial resolution and the better temporal resolution. With our retrievals it is possible to observe the radiative effect of small-scale features such as cumulus clouds, cirrus clouds, or aircraft contrails. The spatial resolution of SEVIRI is 3 km &times 3 km in the sub-satellite point, remarkably better than that of CERES (20 km) or GERB (45 km). The temporal resolution is 15 min (5 min in the rapid-scan mode), the same as GERB, but significantly better than that of CERES which, being on board of a polar orbiting satellite, has a temporal resolution as low as 2 overpasses per day.

Airborne measurements of Lidar backscatter, aerosol concentrations (particle diameters of 4 nm to 50 μm), trace gas mixing ratios (SO2, CO, O3, H2O), single particle properties, and meteorological parameters have been performed in volcanic ash plumes with the Falcon aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). A series of 17 flights was performed over Europe between Southern Germany and Iceland during the eruption period of the Eyjafjalla1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with Lidar directly over the volcano and up to a distance of 2700 km downwind. Lidar and in-situ measurements covered plume ages of 7 h to 120 h. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentration was evaluated for a material density of 2.6 g cm−3 and for either weakly or moderately absorbing coarse mode particles (refractive index 1.59+0i or 1.59+0.004i). In the absorbing case, the ash concentration is about a factor of four larger than in the non-absorbing limit. Because of sedimentation constraints, the smaller results are the more realistic ones for aged plumes. The Falcon flew in ash clouds up to about 1 mg m−3 for a few minutes and in an ash cloud with more than 0.2 mg m−3 mean-concentration for about one hour without engine damages. In fresh plumes, the SO2 concentration was correlated with the ash mass concentration. Typically, 0.5 mg m−3 ash concentration was related to about 100 nmol mol−31 SO2 mixing ratio and 70 nmol mol−1 CO mixing ratio increases for this volcano period. In aged plumes, layers with enhanced coarse mode particle concentration but without SO2 enhancements occurred. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. The ash plumes were often visible as faint dark layers even for concentrations below 0.1 mg m−3. The ozone concentrations and the humidity inside the plumes were often reduced compared to ambient values. The large abundance of volatile Aitken mode particles suggests nucleation of sulfuric acid droplets. Ammonium sulfate particles were also found on the impactors. The effective diameters decreased from about 5 μm in the fresh plume to about 1 μm for plume ages of up to 6 days. The distal ash mass flux on 2 May was of the order 1800 kg s−1; the SO2 mass flux was about a factor of 3–4 smaller. The volcano ejected about 40 Tg of ash mass and 10 Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash. The data described may be used for further studies, including comparisons to satellite and ground or space based Lidar observations, and for model improvements. 1 Also known as Eyjafjallajökull or Eyjafjöll volcano, http://www.britannica.com/EBchecked/topic/1683937/Eyjafjallajokull-volcano

A method designed to track the life cycle of contrail-cirrus using satellite data with high temporal and spatial resolution, from its formation to the final dissolution of the aviation-induced cirrus cloud is presented. The method follows the evolution of contrails from their linear stage until they are undistinguishable from natural cirrus clouds. Therefore, the study of the effect of aircraft-induced clouds in the atmosphere is no longer restricted to linear contrails and can include contrail-cirrus. The method takes advantage of the high spatial resolution of polar orbiting satellites and the high temporal resolution of geostationary satellites to identify the pixels that belong to an aviation induced cloud. The high spatial resolution data of the MODIS sensor is used for contrail detection, and the high temporal resolution of the SEVIRI sensor in the Rapid Scan mode is used for contrail tracking. An example is included in which the method is applied to the study of a long lived contrail over the bay of Biscay.

For the first time the contrail cover for a region covering Thailand and surrounding regions as well as for the region of Japan and its surroundings are determined by remote sensing observations. Locally received NOAA/AVHRR satellite data are analysed by a fully automated contrail detection algorithm. For both regions approx. 400 NOAA-14 satellite scenes from four months of the year 1998 were analysed. Both regions show sufficient air traffic to produce an observable amount of contrails. Thus we are able to measure for the first time contrail frequencies in the tropics and compare it to a nearby mid latitudinal region. The annual average of the daily mean contrail cloud coverage is 0.13% for the Thailand region and about 0.25% for the Japan region. For both regions the contrail cover is largest during spring. The daily cycle shows surprisingly high contrail coverage during night in spite of lower air traffic densities during night time. The satellite observed contrail cover is compared with simulations of contrails by use of the general circulation model ECHAM4 related to air traffic emissions of 1992. While the derived patterns of the regional contrail distributions agree well, the contrail coverage derived from satellite data is larger than the simulated coverage. This discrepancy appears to be mainly due to an increase in air traffic in the time period between the model study and the observations.

Modifications of existing clouds by the exhaust of ships are well-known but poorly studied atmospheric effects which could contribute to climate change. The perturbation of a cloud layer by ship-generated aerosol changes the cloud reflectivity and is identified by long curves in satellite images, known as ship tracks. As ship tracks indicate a pollution of a very clean marine environment and also affect the radiation budget below and above the cloud, it is important to investigate their radiative and climatic effects. Satellite-data from MODIS on Terra are used to examine a scene from 10 February 2003 where ship tracks were detected close to the North American West-Coast. The cloud optical and microphysical properties are derived using a semi-analytical retrieval technique combined with a look-up-table approach. Ship-track-pixels are distinguished from the unperturbed cloud pixels and the optical properties of the former are compared to those of the latter. Within the ship tracks a significant change in the droplet number concentration, the effective radius and the optical thickness are found compared to the unaffected cloud. Significant increase of liquid water could not be confirmed. The resulting cloud properties are used to calculate the radiation budget below and above the cloud. Assuming a mean solar zenith angle, the mean surface radiation below the ship track is decreased by 43.25 Wm?2 and the mean reflectance at TOA is increased by 40.73 Wm?2. For the selected scene the ship emission decreases the solar radiation at the surface by 2.10 Wm?2 and increases the backscattered solar radiation at top of the atmosphere (TOA) by 2.00 Wm?2. Increased backscattered radiation is partly compensated by a decrease of the thermal radiation of 0.43 Wm?2. The resulting net-effect at TOA is an increase of 1.57 Wm?2 corresponding to a negative radiative forcing and a cooling.

Ground-based measurements of solar beam irradiance are expensive and rarely available especially in the sunbelt countries, the favourable regions for concentrating solar energy techniques. A method based on satellite data is presented that calculates hourly solar direct normal irradiance for large regions and for many years with high spatial resolution independently from ground measurements. The attenuation of solar irradiance due to scattering and absorption in the cloud-free atmosphere is calculated by a clear-sky broadband parameterisation model. It uses ozone optical depth from the Total Ozone Mapping Spectrometer, aerosol optical depth from the Global Aerosol Climatology Project and water vapour from the reanalysis of the National Centers for Environmental Prediction. Attenuation due to clouds is taken into account by a cloud index that is derived from the infrared and the visible channel of the geostationary Meteosat weather satellites. As clouds have the strongest impact on beam irradiance at ground, the resolution of the cloud parameterisation dominates the overall spatial and temporal resolution. The presented algorithm provides hourly data of direct normal irradiance related to the nominal 5 × 5 km 2 resolution of Meteosat.

The mean of the heterogeneity-corrected AVHRR-derived contrail coverage reached 0.5%/spl plusmn/0.25% over Western Europe. The authors recognize strong temporal and spatial variations in contrail coverage which match those derived by S. Bakan et al. (1994). Absolute values derived are smaller by a factor of 1.6 which is of low significance due to analysis of different time-periods. Large differences of the two investigations can also be explained by an overestimation of the visual interpretations, but also by the poor detection efficiency of the automated scheme. For the midseason month within this period the authors derive a nighttime contrail coverage of 0.2% which has to be compared to 0.7% for the same period from AVHRR-nonpassages. The observed annual cycle has its maxima during winter and spring, but might still be influenced by a differing detection efficiency. Beyond this the scheme is not able to detect atypical contrails such as very wide spread and fuzzy ones, which are hard to distinguish from natural cirrus. These man made cirrus clouds might have an important influence on the regional climate.

Solar thermal power plants will provide a major share of the renewable energy sources needed in the future. STEPS, an evaluation system for solar thermal power stations, was designed to calculate the performance of such power stations as a function of direct solar radiation, geographical conditions (land slope, land cover, distance from cooling water resources, etc.), infrastructure (pipelines, electricity grids, streets etc.) and the configuration and performance of a selected solar thermal power plant concept. A cloud index derived from METEOSAT satellite images is used to calculate the direct solar radiation resource. A geographic information system (GIS) is used to process all the parameters for site assessment. In order to demonstrate the concept, an analysis of Northern Africa was performed with STEPS providing a ranking of sites with respect to the potential and cost of solar thermal electricity for a particular power plant configuration. Results were obtained with high spatial and temporal resolution.

Our AVHRR volcano and fire data are in agreement with Setzer and Verstraete, showing that when channel 3 saturates the digital number (DN) recorded is greater than zero. The radiance at which this occurs varies within a single radiometer, and from platform to platform. It appears that non-zero saturation has affected all the thermal channels on all AVHRR instruments to date and may be due to the design of the analogue-to-digital converter circuits. Since the exact relation between non-zero DN and spectral radiance is not known, we suggest that all DN over high temperature targets that arc less than or equal to the non-zero saturation DN cannot be trusted to be reliable measurements of spectral radiance.

Contrails are produced by airtraffic and thereby form an anthropogenic component of cloudiness. They typically appear in height levels between approximately 6km and 12km. Their temperature is typically between -40°C and -60°C. Due to these low temperatures their greenhouse effect is potentially high and the question arises to which extent they influence the climate (U. Schumann et a!., 1 994). A prerequisite for an estimation of this climatic influence is a knowledge of the cloud cover which is due to contrails. Our study presents two methods of determining contrail cloud cover using NOAA-AVHRR satellite data. The temperature difference image between channels 4 and 5 at 1 1 .tm and I 2tm enhances the appearence of high level thin clouds and is therefore used as a basis of the analysis. The first method is 'manually', the second by application of an automated detection. Both methods are applied on a scene over Central Europe and compared to each other. Chapter 2 describes the manual analysis and its results, chapter 3 the automated method and its limitations which exist up to now and chapter 4 shows the comparison of the two methods.

The motion of the Earth’s atmosphere is driven by differential heating. The reservoir of the available potential energy, which describes the difference between the actual state of the atmosphere and a hypothetical atmosphere at rest, is estimated to be about 55 x 105 Jm−2 as a mean value around the globe. This reservoir feeds the reservoir of kinetic energy (15 x 105 Jm−2), from where the energy dissipates into heat with a rate of 2.3 Wm−2. As these reservoirs are fairly constant in a climatological sense, the production rate of available potential energy and the transformation rate into kinetic energy has also to be 2.3 Wm−2. In traditional weather forecast models it was not necessary to put much effort into a precise description of the differential heating, the main source of available potential energy, because the time to exhaust the reservoirs mentioned above is given in months.

[1] The influence of contrails on the radiation budget depends mainly on their coverage and optical depth. This study derives these parameters from data of the advanced very high resolution radiometer sensor onboard the NOAA 14 satellite for a region over western Europe within 40°–56°N and 10°W–23°E during 2 years starting March 1995. The data are classified by an operational contrail detection algorithm with a new evaluation of the detection efficiency. From the classification results, daytime and nighttime coverage by line-shaped contrails over western Europe are derived. The daytime contrail coverage for the analyzed region is 0.7% in the annual mean, 1.0% during winter, and 0.4% during summer. The daytime contrail cover is 3 times higher than the night-time contrail cover. An effective optical depth of the observed contrails is derived from the radiation contrasts in the 11 μm channel for contrails and adjacent pixels. The optical depth in the visible spectral range is computed from these results assuming a previously measured size spectrum of ice crystals. The mean visible optical depth is found to be about 0.1, much smaller than that derived from previous case studies. The average radiative forcing at the top of the atmosphere is computed for the derived contrail cloud cover and optical depth. Here contrails mostly cause positive radiative forcing (heating). Larger heating effects during night and summer get partly compensated through more contrail cover during day and winter. The radiative forcing by contrails in the examined region is ∼0.03 W m−2, which is much smaller than was estimated earlier.

From theoretical considerations on the surface energy budget, the concepts for thermal inertia mapping of land-surface is derived. With the aid of an atmospheric radiation transfere model, the physical background for remote sensing of surface temperature is given. Applications, including own work on surface temperatures in alpine regions, are introduced.

Aircraft contribute to global and regional climate changes by contrail formation and by emissions of carbon dioxide and others species. Among these, contrails are considered to have the largest warming contribution on short time scales (up to order of decades) while carbon dioxide may cause the largest warming effect globally at long time scales (order of a century). Contrails warm generally during night. During day contrails may cause a cooling. This paper discusses various strategies to reduce the global warming from aircraft by contrail formation and carbon dioxide emissions. In particular, we discuss the impact of changes of the flight level, typically 2000 ft (610 m) up or down. Previous studies suggested reducing contrail formation by flying lower generally or by flying higher or lower at the actual level with minimum relative humidity. This paper introduces a more efficient strategy which selects optimized routes based on the climate impact of contrails and fuel consumption along these routes. By preferred flights in atmospheric regions where contrails cool, an aircraft routing can be designed with minimum or even negative climate impact. For the fleet as a whole the climate impact is measured in terms of its radiative forcing RF. For individual flights, the climate impact is measured by the amount of energy induced into the Earth-atmosphere system per unit flight distance, which we call the energy forcing EF. Both RF and EF for contrails and CO2 can be combined into a global mean surface temperature increase for a given time horizon. This paper describes the basic principles and quantifies the potential impacts using the recently developed Contrail Cirrus Simulation Prediction tool (CoCiP).