714 research outputs found
Tethered balloon measurements during Arctic autumn conditions in the framework of HALO-(AC)3
The BalloonbornE moduLar Utility for profilinG the lower Atmosphere
(BELUGA) was deployed in autumn 2021 in the Arctic at the AWIPEV research station
in Ny-Ålesund (Svalbard). In-situ profiles of thermodynamic parameters, broadband
radiation, turbulence, aerosol particle concentrations, and cloud microphysical structure,
were performed. Additionally, samples of ice nucleating particles were collected.
Thermal infrared radiation profiles are presented for different cloud conditions. The
data provides the base for studying the vertical distribution of cloud radiative effects,
and extends the common view of the bi-modal distribution of the Arctic surface energy
budget.Das Fesselballonsystem BalloonbornE moduLar Utility for profilinG
the lower Atmosphere (BELUGA) wurde im Herbst 2021 an der Forschungsstation
Ny-Ålesund in der Arktis eingesetzt. Es wurden In-situ Profile von thermodynamischen
Parametern, breitbandiger Strahlung, Turbulenz, Aerosolpartikelkonzentrationen
und der mikrophysikalischer Wolkenstruktur erstellt. Zusätzlich wurden Proben von
eiskeimbildenden Partikeln gesammelt. Strahlungsprofile wurden unter verschiedenen
Wolkenbedeckungen gemessen und quantifizieren die vertikale Verteilung der Wolkenstrahlungseffekte.
Die Profilmessungen erweitern damit die für bodennahe Messungen
bekannte modale Verteilung des Energiehaushalts der Arktis
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The new BELUGA setup for collocated turbulence and radiation measurements using a tethered balloon: First applications in the cloudy Arctic boundary layer
The new BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) tethered balloon system is introduced. It combines a set of instruments to measure turbulent and radiative parameters and energy fluxes. BELUGA enables collocated measurements either at a constant altitude or as vertical profiles up to 1.5km in height. In particular, the instrument payload of BELUGA comprises three modular instrument packages for high-resolution meteorological, wind vector and broadband radiation measurements. Collocated data acquisition allows for estimates of the driving parameters in the energy balance at various heights. Heating rates and net irradiances can be related to turbulent fluxes and local turbulence parameters such as dissipation rates. In this paper the technical setup, the instrument performance, and the measurement strategy of BELUGA are explained. Furthermore, the high vertical resolution due to the slow ascent speed is highlighted as a major advantage of tethered balloon-borne observations. Three illustrative case studies of the first application of BELUGA in the Arctic atmospheric boundary layer are presented. As a first example, measurements of a single-layer stratocumulus are discussed. They show a pronounced cloud top radiative cooling of up to 6K h-1. To put this into context, a second case elaborates respective measurements with BELUGA in a cloudless situation. In a third example, a multilayer stratocumulus was probed, revealing reduced turbulence and negligible cloud top radiative cooling for the lower cloud layer. In all three cases the net radiative fluxes are much higher than turbulent fluxes. Altogether, BELUGA has proven its robust performance in cloudy conditions of the Arctic atmospheric boundary layer
Influence of local surface albedo variability and ice crystal shape on passive remote sensing of thin cirrus
Airborne measurements of solar spectral radiance reflected by cirrus are
performed with the HALO-Solar Radiation (HALO-SR) instrument onboard the High
Altitude and Long Range Research Aircraft (HALO) in November 2010. The data
are used to quantify the influence of surface albedo variability on the
retrieval of cirrus optical thickness and crystal effective radius. The
applied retrieval of cirrus optical properties is based on a standard two-wavelength approach utilizing measured and simulated reflected radiance in
the visible and near-infrared spectral region. Frequency distributions of the
surface albedos from Moderate resolution Imaging Spectroradiometer (MODIS)
satellite observations are used to compile surface-albedo-dependent lookup
tables of reflected radiance. For each assumed surface albedo the cirrus
optical thickness and effective crystal radius are retrieved as a function of
the assumed surface albedo. The results for the cirrus optical thickness are
compared to measurements from the High Spectral Resolution Lidar (HSRL). The
uncertainty in cirrus optical thickness due to local variability of surface
albedo in the specific case study investigated here is below 0.1 and thus
less than that caused by the measurement uncertainty of both instruments. It
is concluded that for the retrieval of cirrus optical thickness the surface
albedo variability is negligible. However, for the retrieval of crystal effective
radius, the surface albedo variability is of major importance,
introducing uncertainties up to 50%. Furthermore, the influence of the
bidirectional reflectance distribution function (BRDF) on the retrieval of
crystal effective radius was investigated and quantified with uncertainties
below 10%, which ranges below the uncertainty caused by the surface albedo
variability. The comparison with the independent lidar data allowed for
investigation of the role of the crystal shape in the retrieval. It is found that
if assuming aggregate ice crystals, the HSRL observations fit best with the
retrieved optical thickness from HALO-SR
Atmospheric radiative effects of an in situ measured Saharan dust plume and the role of large particles
This work will present aerosol size distributions measured in a Saharan dust plume between 0.9 and 12 km altitude during the ACE-2 campaign 1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope of sensitivity studies considering varied input parameters like solar zenith angle, scaled total dust optical depth, tropospheric standard aerosol profiles and particle complex refractive index. The results indicate that the large particle fraction has a predominant impact on the optical properties of the dust. A single scattering albedo of ω<sub><I>o</I></sub>=0.75&ndash;0.96 at 550 nm was simulated in the entire dust column as well as 0.76 within the Saharan dust layer at ~4 km altitude indicating enhanced absorption. The measured dust leads to cooling over the ocean but warming over the desert due to differences in their spectral surface albedo and surface temperature. The large particles absorb strongly and they contribute at least 20% to the ARE in the dusty atmosphere. <br><br> From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median diameter of ~9 μm and a column single scattering albedo of 0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles
Forest albedo in the context of different cloud situations derived from irradiance measurements at the Leipzig floodplain crane: A pilot study
The surface albedo significantly modulates the atmospheric energy budget
and, thus, vertical radiation, energy, and mass fluxes. Therefore, it regulates the local
and regional effects of climate warming. Over a forest canopy, the surface albedo mainly
depends on the seasonal leaf state. Furthermore, for certain surface types, such as snow,
it has been shown that the surface albedo changes as a function of cloudiness. A similar
effect is expected over forest surfaces, leading to complex feedback loops between forest
surfaces and climate. To investigate these processes, a pilot study was performed at the
Leipzig floodplain crane to observe the forest canopy albedo under different atmospheric
conditions in 2021. First analyses revealed a dependency of the forest albedo from the
cloud state, which is slightly stronger in the near-infrared wavelength range compared to
the visible wavelength range.Der atmosphärische Strahlungshaushalt und damit auch die vertikale
Strahlungsverteilung, Energie- und Massenflüsse werden signifikant durch die
Bodenalbedo gesteuert. Diese regulieren somit lokale und regionale Effekte der Klimaerwärmung.
Über einem Wald hängt die Bodenalbedo hauptsächlich vom saisonalen
Blattstatus ab. Zudem wurde für bestimmte Bodentypen wie Schneeoberflächen gezeigt,
dass die Bodenalbedo eine Funktion der Bewölkung ist. Ähnlicher Effekte werden für
Waldoberflächen erwartet, welche zu komplexen Rückkopplungseffekten zwischenWaldoberflächen
und dem Klima führen. Um diese Prozesse zu untersuchen wurde im Jahr
2021 eine Vorstudie am Leipziger Auwaldkran durchgeführt, um die Waldalbedo unter
verschiedenen atmosphärischen Bedingungen zu beobachten. Erste Analysen zeigen,
dass auch die Albedo des Waldes von den Bewölkungsbedingungen abhängt. Der Effekt
ist dabei etwas stärker im nah-infrarotem als im sichtbaren Wellenlängenbereich zu
beobachten
CIRRUS-HL: Overview of LIM contributions
From June to July 2021, the Leipzig Institute for Meteorology (LIM)
participated in the Cirrus in High Latitudes (CIRRUS-HL) campaign. Utilizing the
German High Altitude Long Range Research Aircraft (HALO), 24 research flights were
conducted out of Oberpfaffenhofen, Germany. The initial goal of the campaign was
to sample high-latitude cirrus clouds with a combination of in-situ and remote sensing
instrumentation. However, due to the global coronavirus pandemic, the flights had to
be carried out from southern Germany instead of northern Sweden. Thus, the flight
time in Arctic latitudes was limited. Therefore, more objectives concerning midlatitude
cirrus were included in the campaign goals. LIM contributed to CIRRUS-HL with
measurements by the Broadband AirCrAft RaDiometer Instrumentation (BACARDI)
and the Spectral Modular Airborne Radiation measurement sysTem (SMART). While
BACARDI measured broadband solar and terrestrial upward and downward irradiance,
SMART measured spectrally resolved solar upward radiance as well as upward and
downward irradiance.Von Juni bis Juli 2021 nahmen einige Mitarbeitende des LIM
an der CIRRUS-HL Kampagne teil. Mit dem deutschen Forschungsflugzeug HALO
(High Altitude Long Range Research Aircraft) wurden 24 Forschungsflüge von Oberpfaffenhofen,
Deutschland, aus durchgeführt. Ursprüngliches Ziel der Kampagne war es,
Zirruswolken in hohen Breitengraden mit einer Kombination aus In-situ- und Fernerkundungsinstrumenten
zu untersuchen. Aufgrund der weltweiten Corona-Pandemie mussten
die Flüge jedoch von Süddeutschland statt von Nordschweden aus durchgeführt werden.
Daher wurden weitere Ziele in Bezug auf Zirruswolken in mittleren Breiten in die Ziele
der Kampagne aufgenommen. Das LIM-Team betrieb die breitbandigen und spektralen
Strahlungssensoren BACARDI (Broadband AirCrAft RaDiometer Instrumentation) und
SMART (Spectral Modular Airborne Radiation measurement sysTem), wobeiBACARDI
die breitbandige solare und terrestrische Auf- und Abwärtsstrahlung und SMART die
spektral aufgelöste solareAuf- undAbwärtsstrahlung sowie dieAufwärtsstrahlungsdichte
maß
Parameterizing anisotropic reflectance of snow surfaces from airborne digital camera observations in Antarctica
The surface reflection of solar radiation comprises an important boundary condition for solar radiative transfer simulations. In polar regions above snow surfaces, the surface reflection is particularly anisotropic due to low Sun elevations and the highly anisotropic scattering phase function of the snow crystals. The characterization of this surface reflection anisotropy is essential for satellite remote sensing over both the Arctic and Antarctica. To quantify the angular snow reflection properties, the hemispherical-directional reflectance factor (HDRF) of snow surfaces was derived from airborne measurements in Antarctica during austral summer in 2013/14. For this purpose, a digital 180∘ fish-eye camera (green channel, 490–585 nm wavelength band) was used. The HDRF was measured for different surface roughness conditions, optical-equivalent snow grain sizes, and solar zenith angles. The airborne observations covered an area of around 1000 km × 1000 km in the vicinity of Kohnen Station (75∘0′ S, 0∘4′ E) at the outer part of the East Antarctic Plateau. The observations include regions with higher (coastal areas) and lower (inner Antarctica) precipitation amounts and frequencies. The digital camera provided upward, angular-dependent radiance measurements from the lower hemisphere. The comparison of the measured HDRF derived for smooth and rough snow surfaces (sastrugi) showed significant differences, which are superimposed on the diurnal cycle. By inverting a semi-empirical kernel-driven bidirectional reflectance distribution function (BRDF) model, the measured HDRF of snow surfaces was parameterized as a function of solar zenith angle, surface roughness, and optical-equivalent snow grain size. This allows a direct comparison of the HDRF measurements with the BRDF derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite product MCD43. For the analyzed cases, MODIS observations (545–565 nm wavelength band) generally underestimated the anisotropy of the surface reflection. The largest deviations were found for the volumetric model weight fvol (average underestimation by a factor of 10). These deviations are likely linked to short-term changes in snow properties
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