Manfred Wendisch - Academia.edu (original) (raw)

Papers by Manfred Wendisch

The realistic representation of aerosol-cloud interactions is of primary importance for accurate ... more The realistic representation of aerosol-cloud interactions is of primary importance for accurate climate model projections. The investigation of these interactions in strongly contrasting clean and polluted atmospheric conditions in the Amazon region has been one of the motivations for several field campaigns, including the airborne "Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems-Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON-CHUVA)" campaign based in Manaus, Brazil, in September 2014. In this work we combine in situ and remotely sensed aerosol, cloud, and atmospheric radiation data collected during ACRIDICON-CHUVA with regional, online-coupled chemistry-transport simulations to evaluate the model's ability to represent the indirect effects of biomass burning aerosol on cloud microphysical and optical properties (droplet number concentration and effective radius). We found agreement between the modeled and observed median cloud droplet number concentration (CDNC) for low values of CDNC, i.e., low levels of pollution. In general, a linear relationship between modeled and observed CDNC with a slope of 0.3 was found, which implies a systematic underestimation of modeled CDNC when compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations was also underestimated, and cloud droplet effective radii (r eff) were overestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN cm −3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Additional CCN emitted from local fires did not cause a notable change in modeled cloud droplet effective radii. Finally, we also evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, showing that we are able to derive CDNC at cloud base from cloud-side remote-sensing observations.

Scientific Data, Dec 29, 2022

Two airborne field campaigns focusing on observations of Arctic mixed-phase clouds and boundary l... more Two airborne field campaigns focusing on observations of Arctic mixed-phase clouds and boundary layer processes and their role with respect to Arctic amplification have been carried out in spring 2019 and late summer 2020 over the Fram Strait northwest of Svalbard. The latter campaign was closely connected to the Multidisciplinary drifting Observatory for the Study of arctic Climate (MOSaiC) expedition. Comprehensive datasets of the cloudy Arctic atmosphere have been collected by operating remote sensing instruments, in-situ probes, instruments for the measurement of turbulent fluxes of energy and momentum, and dropsondes on board the AWI research aircraft Polar 5. In total, 24 flights with 111 flight hours have been performed over open ocean, the marginal sea ice zone, and sea ice. The datasets follow documented methods and quality assurance and are suited for studies on arctic mixedphase clouds and their transformation processes, for studies with a focus on arctic boundary layer processes, and for satellite validation applications. All datasets are freely available via the world data center PANGAEA.

Atmospheric Chemistry and Physics, May 12, 2020

The combination of downward-looking airborne lidar, radar, microwave, and imaging spectrometer me... more The combination of downward-looking airborne lidar, radar, microwave, and imaging spectrometer measurements was exploited to characterize the vertical and smallscale (down to 10 m) horizontal distribution of the thermodynamic phase of low-level Arctic mixed-layer clouds. Two cloud cases observed in a cold air outbreak and a warm air advection event observed during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign were investigated. Both cloud cases exhibited the typical vertical mixed-phase structure with mostly liquid water droplets at cloud top and ice crystals in lower layers. The horizontal, small-scale distribution of the thermodynamic phase as observed during the cold air outbreak is dominated by the liquid water close to the cloud top and shows no indication of ice in lower cloud layers. Contrastingly, the cloud top variability in the case observed during a warm air advection showed some ice in areas of low reflectivity or cloud holes. Radiative transfer simulations considering homogeneous mixtures of liquid water droplets and ice crystals were able to reproduce the horizontal variability in this warm air advection. Large eddy simulations (LESs) were performed to reconstruct the observed cloud properties, which were used subsequently as input for radiative transfer simulations. The LESs of the cloud case observed during the cold air outbreak, with mostly liquid water at cloud top, realistically reproduced the observations. For the warm air advection case, the simulated ice water content (IWC) was systematically lower than the measured IWC. Nevertheless, the LESs revealed the presence of ice particles close to the cloud top and confirmed the observed horizontal variability in the cloud field. It is concluded that the cloud top smallscale horizontal variability is directly linked to changes in the vertical distribution of the cloud thermodynamic phase. Passive satellite-borne imaging spectrometer observations with pixel sizes larger than 100 m miss the small-scale cloud top structures.

This study analyzes the surface cloud radiative effect (CRE) obtained during airborne observation... more This study analyzes the surface cloud radiative effect (CRE) obtained during airborne observations of three campaigns in the Arctic northwest of Svalbard. The surface CRE quantifies the potential of clouds to modify the radiative energy budget of the surface and is calculated by combining broadband radiation measurements during low-level flight sections in mostly cloudy conditions with radiative transfer simulations of cloud-free conditions. The significance of surface albedo changes due to the presence of clouds is demonstrated and this effect is considered in the cloud-free simulations. The observations are discussed with respect to differences of the CRE between sea ice and open ocean surfaces, and between the seasonally different campaigns. The results indicate that the CRE depends on both cloud, illumination, surface, and thermodynamic properties. The solar and thermal-infrared (TIR) component of the CRE are analyzed separately and in combination. The inter-campaign differences of the solar CRE are dominated by the seasonal cycle of the solar zenith angle, with the largest cooling effect in summer. The lower surface albedo causes a larger solar cooling effect over open ocean than over sea ice, which amounts to −259 W m −2 (−108 W m −2) and −65 W m −2 (−17 W m −2), respectively, during summer (spring). Independent of campaign and surface type, the TIR CRE is only weakly variable and shows values around 75 W m −2. In total, clouds show a cooling effect over open ocean during all campaigns. In contrast, clouds over sea ice exert a warming effect to the surface, which neutralizes during midsummer. Given the seasonal cycle of the sea ice distribution, these results imply that clouds in the Fram Strait region cool the surface during the sea ice minimum in late summer, while they warm the surface during the sea ice maximum in spring. 1 Introduction The enhanced warming and the rapid loss of sea ice are the most obvious signs of accelerated climate changes currently ongoing in the Arctic. Because these changes appear much faster compared to the rest of the globe, the term Arctic amplification was introduced (Serreze and Barry, 2011; Wendisch et al., 2017, 2022a). A multitude of atmospheric processes and feedback mechanisms contributes to this amplified transformation of the Arctic climate system. Clouds play a substantial, yet not fully understood, role in Arctic amplification by their involvement in several feedbacks. For example, the downward radiative energy fluxes in the thermal-infrared (TIR) spectral range (∼ 4-100 µm) are increased by clouds, which leads to a warmer surface and delayed refreezing, thinner sea ice, and faster melting (positive cloud-sea ice feedback, Morrison et al., 2019). At the same time, the increased fraction of liquid water in the clouds increases the cloud optical thickness and the reflection of solar radiation (∼ 1

During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR), which was conducte... more During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR), which was conducted in Svalbard in March and April 2007, tropospheric Arctic clouds were observed with two ground-based backscatter lidar systems (micro pulse lidar and Raman lidar) and with an airborne elastic lidar. An increase in low-level (cloud tops below 2.5 km) cloud cover from 51% to 65% was observed above Ny-Ålesund during the time of the ASTAR campaign. Four different case studies of lidar cloud observations are analyzed: With the ground-based Raman lidar, a pre-condensation layer was observed at an altitude of 2 km. The layer consisted of small droplets with a high number concentration (around 300 cm −3) at low temperatures (−30 • C). Observations of a boundary layer mixed-phase cloud by airborne lidar were evaluated with the measurements of concurrent airborne in situ and spectral solar radiation sensors. Two detailed observations of multiply layered clouds in the free troposphere are presented. The first case was composed of various ice layers with different optical properties detected with the Raman lidar, the other case showed a mixed-phase double layer and was observed by airborne lidar. The analysis of these four cases confirmed that lidar data provide information of the whole range from subvisible to optically thick clouds. Despite the attenuation of the laser signal in optically thick clouds and multiple scattering effects, information on the geometrical boundaries of liquid water clouds were obtained. Furthermore, the dominating phase of the clouds' particles in the layer closest to the lidar system could be retrieved.

Atmospheric Chemistry and Physics Discussions, 2017

Vertical profiles of the cloud particle phase state in tropical deep-convective clouds (DCCs) wer... more Vertical profiles of the cloud particle phase state in tropical deep-convective clouds (DCCs) were investigated using airborne solar radiation data collected by the German research aircraft HALO during the ACRIDICON-CHUVA campaign, which was conducted over the Brazilian Amazon in September 2014. A phase discrimination retrieval based on imaging spec-troradiometer measurements of cloud side spectral reflectivity was applied to DCCs under different aerosol conditions. From the retrieval results the height of the mixed phase layer of the DCCs was determined. The retrieved profiles were compared with in situ measurements and satellite observations. It was found that the depth and vertical position of the mixed phase layer can vary up to…

Spectral optical layer properties of cirrus are derived from simultaneous and vertically collocat... more Spectral optical layer properties of cirrus are derived from simultaneous and vertically collocated measurements of spectral upward and downward solar irradiance above and below the cloud layer and concurrent in situ microphysical sampling. From the irradiance data spectral transmissivity, absorptivity, reflectivity, and cloud top albedo of the observed cirrus layer are obtained. At the same time microphysical properties of the cirrus were sampled. The close collocation of the radiative and microphysical measurements, above, beneath and inside the cirrus, is obtained by using a research aircraft (Learjet 35A) in tandem with a towed platform called AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected in two field campaigns above the North and Baltic Sea in spring and late summer 2013. Exemplary results from one measuring flight are discussed also to illustrate the benefits of collocated sampling. Based on the measured cirrus microphysical properties, radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius r eff , and optical thickness τ on cirrus optical layer properties. The effects of clouds beneath the cirrus are evaluated in addition. They cause differences in the layer properties of the cirrus by a factor of 2 to 3, and for cirrus radiative forcing by up to a factor of 4. If low-level clouds below cirrus are not considered the solar cooling due to the cirrus is significantly overestimated.

The two concerted field campaigns, Arctic CLoud Observations Using airborne measurements during p... more The two concerted field campaigns, Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) and the Physical feedbacks of Arctic planetary boundary level Sea ice, Cloud and AerosoL (PASCAL), took place near Svalbard from 23 May to 26 June 2017. They were focused on studying Arctic mixed-phase clouds and involved observations from two airplanes (ACLOUD), an icebreaker (PASCAL) and a tethered balloon, as well as ground-based stations. Here, we present the synoptic development during the 35-day period of the campaigns, using near-surface and upper-air meteorological observations, as well as operational satellite, analysis, and reanalysis data. Over the campaign period, short-term synoptic variability was substantial, dominating over the seasonal cycle. During the first campaign week, cold and dry Arctic air from the north persisted, with a distinct but seasonally unusual cold air outbreak. Cloudy conditions with mostly low-level clouds prevailed. The subsequent 2 weeks were characterized by warm and moist maritime air from the south and east, which included two events of warm air advection. These synoptical disturbances caused lower cloud cover fractions and higherreaching cloud systems. In the final 2 weeks, adiabatically warmed air from the west dominated, with cloud properties strongly varying within the range of the two other periods. Results presented here provide synoptic information needed to analyze and interpret data of upcoming studies from ACLOUD/PASCAL, while also offering unprecedented measurements in a sparsely observed region.

EGU General Assembly Conference Abstracts, May 1, 2010

AGUFM, Dec 1, 2009

ABSTRACT We present a new method to measure the spectral absorption properties of aerosol layers.... more ABSTRACT We present a new method to measure the spectral absorption properties of aerosol layers. Combined airborne spectral measurements of irradiance and actinic flux density can be employed to estimate the spectral mean absorption coefficient of an atmospheric layer. If extinction measurements, e.g. from a LIDAR, are also available, then the spectral single-scattering albedo of that layer can be derived as well. The application of this new method is presented for different aerosol types: mineral dust (SAMUM experiment, Morocco, 2006), rural (INSPECTRO, Germany, 2004), and Arctic haze (ARCTAS/ARCPAC, Alaska, 2008). Sensitivity studies based on these experiments show the lower limits for this method.

AGUFM, Dec 1, 2003

ABSTRACT

Applying the cloud regime classification on field data: Size distributions for WBF and CoEx cloud... more Applying the cloud regime classification on field data: Size distributions for WBF and CoEx clouds Correlations between size distribution and water saturation WBF cloud occurrence increases with altitude (=> with decreasing temperature) Process visible: Cloud particles* grow with increasing altitude in the CoEx regime *mean diameter of the cloud particle fraction with the highest concentration (calculated per flight second) Measurement campaigns and results Small particles in the WBF regime confirm the existence of small ice crystals! Cloud regimes ➔ The cloud particle size distribution gives hints at the WBF or CoEx humidity regime

The magnitude of solar radiative effects (cooling or warming) of black carbon (BC) particles embe... more The magnitude of solar radiative effects (cooling or warming) of black carbon (BC) particles embedded in the Arctic atmosphere and surface snow layer was explored on the basis of case studies. For this purpose, combined atmospheric and snow radiative transfer simulations were performed for cloudless and cloudy conditions on the basis of BC mass concentrations measured in pristine early summer and more polluted early spring conditions. The area of interest is the remote sea-ice-covered Arctic Ocean in the vicinity of Spitsbergen, northern Greenland, and northern Alaska typically not affected by local pollution. To account for the radiative interactions between the black-carbon-containing snow surface layer and the atmosphere, an atmospheric and snow radiative transfer model were coupled iteratively. For pristine summer conditions (no atmospheric BC, minimum solar zenith angles of 55 •) and a representative BC particle mass concentration of 5 ng g −1 in the surface snow layer, a positive daily mean solar radiative forcing of +0.2 W m −2 was calculated for the surface radiative budget. A higher load of atmospheric BC representing early springtime conditions results in a slightly negative mean radiative forcing at the surface of about −0.05 W m −2 , even when the low BC mass concentration measured in the pristine early summer conditions was embedded in the surface snow layer. The total net surface radiative forcing combining the effects of BC embedded in the atmosphere and in the snow layer strongly depends on the snow optical properties (snow specific surface area and snow density). For the conditions over the Arctic Ocean analyzed in the simulations, it was found that the atmospheric heating rate by water vapor or clouds is 1 to 2 orders of magnitude larger than that by atmospheric BC. Similarly, the daily mean total heating rate (6 K d −1) within a snowpack due to absorption by the ice was more than 1 order of magnitude larger than that of atmospheric BC (0.2 K d −1). Also, it was shown that the cooling by atmospheric BC of the near-surface air and the warming effect by BC embedded in snow are reduced in the presence of clouds.

Tellus B, Sep 1, 2011

The direct radiative forcing and dynamic atmospheric response due to Saharan dust and biomass-bur... more The direct radiative forcing and dynamic atmospheric response due to Saharan dust and biomass-burning aerosol particles are presented for a case study during the SAMUM-2 field campaign in January and February 2008. The regional model system COSMO-MUSCAT is used. It allows online interaction of the computed dust and smoke load with the solar and terrestrial radiation and with the model dynamics. Model results of upward solar irradiances are evaluated against airborne radiation measurements in the Cape Verde region. The comparison shows a good agreement for the case of dust and smoke mixture. Dust and smoke particles influence the atmospheric dynamics by changing the radiative heating rates. The related pressure perturbations modify local and synoptic scale air-flow patterns. In the radiative feedback simulations, the Hadley circulation is enhanced and convergence zones occur along the Guinea coast. Thus, the smoke particles spread more than 5 • further north and the equatorward transport is reduced. Within the convergence zones, Saharan dust and biomass-burning material are more effectively advected towards the Cape Verdes. Given the model uncertainties, the agreement between the modelled and observed aerosol distribution is locally improved when aerosol-radiation interaction is considered.

Journal of Geophysical Research, Jul 12, 2007

On the basis of a new regional dust model system, the sensitivity of radiative forcing to dust ae... more On the basis of a new regional dust model system, the sensitivity of radiative forcing to dust aerosol properties and the impact on atmospheric dynamics were investigated. Uncertainties in optical properties were related to uncertainties in the complex spectral refractive index of mineral dust. The climatological-based distribution of desert-type aerosol in the radiation scheme of the nonhydrostatic regional model LM was replaced by dust optical properties from spectral refractive indices, derived from in situ measurements, remote sensing, bulk measurements, and laboratory experiments, employing Mie theory. The model computes changes in the solar and terrestrial irradiance from a spatially and temporally varying atmospheric dust load for five size classes. A model study of a Saharan dust outbreak in October 2001 was carried out when large amounts of Saharan dust were transported to Europe. The dust optical thickness computed from the simulation results in values of about 0.5 in large regions of the Saharan desert but can be larger than 5.0 near large dust sources (for example, Bodélé depression). During the dust outbreak, the aerosol in the southern Sahara causes a daytime reduction in 2-m temperature of 3 K in average with differences of 10% depending on used dust optical properties. The simulations indicated that the large variability in radiative properties due to different mixture of clay aggregates in Saharan dust can lead in regional average to differences of up to 48% in net forcing efficiency at top of the atmosphere.

Page 1. Hyperspectral Solar Spectral Measurements and Applications Peter Pilewskie University of ... more Page 1. Hyperspectral Solar Spectral Measurements and Applications Peter Pilewskie University of Colorado, LASP, Campus Box 311, Boulder, Colorado 80309-0392, USA peter.pilewskie@lasp.colorado.edu Sebastian Schmidt ...

Fourier Transform Spectroscopy/ Hyperspectral Imaging and Sounding of the Environment, 2007

Manfred Wendisch Institut für Physik der Atmosphäre, Universität Mainz, Becherweg 21, 55099 Mainz... more Manfred Wendisch Institut für Physik der Atmosphäre, Universität Mainz, Becherweg 21, 55099 Mainz, Germany wendisch@tropos.de ... Ping Yang Department of Atmospheric Sciences, TAMU 3150, Texas A&M University, College Station, Texas 77843, USA pyang@ariel.met.tamu. ...

Elementa, 2022

The tethered balloon-borne measurement system BELUGA (Balloon-bornE moduLar Utility for profilinG... more The tethered balloon-borne measurement system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was deployed over the Arctic sea ice for 4 weeks in summer 2020 as part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition. Using BELUGA, vertical profiles of dynamic, thermodynamic, aerosol particle, cloud, radiation, and turbulence properties were measured from the ground up to a height of 1,500 m. BELUGA was operated during an anomalously warm period with frequent liquid water clouds and variable sea ice conditions. Three case studies of liquid water phase, single-layer clouds observed on 3 days (July 13, 23, and 24, 2020) are discussed to show the potential of the collected data set to comprehensively investigate cloud properties determining cloud evolution in the inner Arctic over sea ice. Simulated back-trajectories show that the observed clouds have evolved within 3 different air masses (“aged Arctic,” “advected over sea ice,” and “advected over open ocean”), which left distinct fingerprints in the cloud properties. Strong cloud top radiative cooling rates agree with simulated results of previous studies. The weak warming at cloud base is mostly driven by the vertical temperature profile between the surface and cloud base. In-cloud turbulence induced by the cloud top cooling was similar in strength compared to former studies. From the extent of the mixing layer, it is speculated that the overall cloud cooling is stronger and thus faster in the warm oceanic air mass. Larger aerosol particle number concentrations and larger sizes were observed in the air mass advected over the sea ice and in the air mass advected over the open ocean.