Radiative budget and cloud radiative effect over the Atlantic from ship-based observations

The aim of this study is to determine cloud-type resolved cloud radiative budgets and cloud radiative effects from surface measurements of broadband radiative fluxes over the Atlantic Ocean. Furthermore, based on simultaneous observations of the state of the cloudy atmosphere, a radiative closure study has been performed by means of the ECHAM5 single column model in order to identify the model's ability to realistically reproduce the effects of clouds on the climate system. An extensive database of radiative and atmospheric measurements has been established along five meridional cruises of the German research icebreaker Polarstern. Besides pyranometer and pyrgeometer for downward broadband solar and thermal radiative fluxes, a sky imager and a microwave radiometer have been utilized to determine cloud fraction and cloud type on the one hand and temperature and humidity profiles as well as liquid water path for warm non-precipitating clouds on the other hand. Averaged over all cruise tracks, we obtain a total net (solar + thermal) radiative flux of 144 W m(-2) that is dominated by the solar component. In general, the solar contribution is large for cirrus clouds and small for stratus clouds. No significant meridional dependencies were found for the surface radiation budgets and cloud effects. The strongest surface longwave cloud effects were shown in the presence of low level clouds. Clouds with a high optical density induce strong negative solar radiative effects under high solar altitudes. The mean surface net cloud radiative effect is -33 W m(-2). For the purpose of quickly estimating the mean surface longwave, shortwave and net cloud effects in moderate, subtropical and tropical climate regimes, a new parameterisation was created, considering the total cloud amount and the solar zenith angle. The ECHAM5 single column model provides a surface net cloud effect that is more cooling by 17 W m(-2) compared to the radiation observations. This overestimation in solar cooling is mostly caused by the shortwave impact of convective clouds. The latter show a large overestimation in solar cooling of up to 114 W m(-2). Mean cloud radiative effects of cirrus and stratus clouds were simulated close to the observations

Validation of downward surface radiation derived from MSG data by in-situ observations over the Atlantic ocean

The present work investigates the quality of the shortwave and and longwave downward radiation (DSR, DLR) at the sea surface over the Atlantic Ocean as retrieved from Meteosat Second Generation (MSG) measurements and EUMETSAT's Climate Monitoring - Satellite Application Facility (CM-SAF) algorithms. The observations taken at two transatlantic research cruises have been an ideal basis to be compared with the MSG products for DSR and DLR derived from Meteosat-8 and Meteosat-9. Onboard the research vessels "Akademik Ioffe" and "Polarstern" high quality in situ measurements of both radiation fluxes have been performed. Continuous full sky imagery and standard meteorological observations enable a comprehensive evaluation of the skills of MSG DSR- and DLR-retrievals in different climate zones and under various cloud and weather conditions. The DSR was retrieved by MSG with a positive bias of 2.77 Wm−2 during the Ioffe cruise, and 22.23 Wm−2 during the Polarstern cruise. The bias for the DLR was −1.73 Wm−2 and 2.76 Wm−2, respectively. The differences between the two cruises mainly arise from the different weather conditions. No significant differences between the satellite products from Meteosat-8 and Meteosat-9 were found. In general DSR and DLR for clear sky conditions are captured with a high accuracy. Largest retrieval errors occur for fast fluctuating broken cloud conditions, though on average the MSG algorithm match the in-situ observations well. Semitransparent cirrus was found to cause a negative bias for the retrieved DSR. In tropics and subtropics the errors for DLR are smaller compared to higher latitudes. Most importantly, no significant dependencies of the satellite retrieval errors for both the DSR and the DLR on the solar elevation, near-surface humidity, cloud cover, SST and the shift of day and night were found, indicating that the CM-SAF radiation products are not subject to significant systematic errors. Diese Arbeit evaluiert die Qualität der abwärtsgerichteten kurzwelligen Einstrahlung (DSR) und der abwärtsgerichteten langwelligen Gegenstrahlung (DLR) an der Meeresoberfläche des Atlantischen Ozeans, berechnet aus Fernerkundungsdaten von Meteosat Second Generation (MSG) mit Hilfe der EUMETSAT Climate Monitoring - Satellite Application Facility (CM-SAF) - Algorithmen. Die auf zwei transatlantischen Forschungsfahrten gewonnenen Beobachtungsdaten stellen eine ideale Basis für den Vergleich mit den MSG-Produkten DSR und DLR dar, die aus Daten des Meteosat-8 und Meteosat-9 abgeleitet wurden. An Bord der Forschungsschiffe Akademik Ioffe und Polarstern wurden hochwertige in situ Messungen beider Strahlungsflüsse durchgeführt. Kontinuierliche Sequenzen der Wolkenkamera in Verbindung mit meteorologischen Standardmessungen ermöglichen diese Vergleichsstudie mit den Ergebnissen der MSG-Algorithmen für DSR und DLR in unterschiedlichen Klimazonen und unter verschiedensten Wolken- und Wetterbedingungen. Für die Fahrt der Ioffe zeigte die DSR abgeleitet aus MSG-Daten eine Überschätzung von 2.77 Wm−2, für die Fahrt der Polarstern wurden 22.23 Wm−2 ermittelt. Der systematische Fehler der DLR war −1.73 Wm−2 bzw. 2.76 Wm−2. Die unterschiedlichen Werte der beiden Fahrten resultieren hauptsächlich aus den verschiedenen Wetterbedingungen. Durch den zeitlichen Überlapp konnten Satellitenprodukte von Meteosat-8 und Meteosat-9 verglichen werden, die keine signifikanten Unterschiede zeigten. Im Allgemeinen werden DSR und DLR im wolkenfreien Fall mit hoher Genauigkeit wiedergegeben. Die größten Fehler im Algorithmus kommen bei sich schnell ändernder Cumulusbedeckung vor, wobei die berechneten Einstrahlungen im Mittel gut mit den in situ Messungen übereinstimmen. Semitransparenter Cirrus verursacht Unterschätzungen in der abgeleiteten DSR. In Tropen und Subtropen sind die Fehler in der DLR geringer als in hohen Breiten. Wichtig ist die Tatsache, dass der Fehler für den Satellitenalgorithmus sowohl für DSR als auch für DLR keine signifikanten Abhängigkeiten von dem Sonnenstand, von der Luftfeuchtigkeit in Bodennähe, vom Wolkenbedeckungsgrad, von der SST und vom Tag-Nacht-Unterschied zeigen. Dies weißt darauf hin, dass die CM-SAF Strahlungsprodukte keinen signifikanten systematischen Fehlern unterliegen

Parametrisierung der solaren Einstrahlung über dem Ozean im Rahmen des "Meridional Ocean Radiation Experiment" MORE

In dieser Arbeit werden verschiedene Parametrisierungen der solaren Einstrahlung unter maritimen Bedingungen untersucht. Sie unterscheiden sich hauptsächlich in den benötigten Eingangsgrößen. Besonderes Augenmerk wird auf die Bilder der Wolkenkamera gerichtet, die eine von synoptischen Wolkenbeobachtungen unabhängige Berechnung der solaren Einstrahlung am Boden ermöglichen. Die Grundlage bildet der Datensatz der ersten Forschungsfahrt des Meridional Ocean Radiation Experiment MORE vom Jahr 2004. Strahlungsparametrisierungen nach Lumb (1964), Lind et al. (1984) und Dobson und Smith (1988) definieren synoptische Wolkenkategorien, innerhalb derer die Transmissivität der bewölkten Atmosphäre approximiert wird. Die Einteilung der Bewölkung in Kategorien ist relativ grob und kann bei geringfügig unterschiedlichen Beobachtungen zu großen Differenzen der berechneten Einstrahlung führen. Die Strahlungsparametrisierung nach Zillman (1972) zeigt gute Übereinstimmungen mit gemessenen solaren Strahlungsflüssen. Die atmosphärische Transmissivität wird aus dem Wasserdampfdruck am Boden und dem Wolkenbedeckungsgrad abgeleitet. Dabei ist die Berechnung des Bedeckungsgrades nach Long und DeLuisi (1998) aus Bildern der Wolkenkamera bei unbewölktem Himmel fehlerhaft. Bei allen Parametrisierungen kann die Einstrahlung bei wolkenfreiem Himmel am genauesten berechnet werden. Durchbrochene Cumulusbewölkung führt zu starken Fluktuationen der Einstrahlung, die aber im Mittel gut wiedergegeben werden kann. Stratiforme Bewölkung führt zu großen Fehlern, da die optische Dicke der Wolkenschicht in den Strahlungsparametrisierungen unberücksichtigt bleibt. Als Ergebnis der Analysen der Strahlungsberechnungen kann die Parametrisierung nach Zillman soweit modifiziert werden, dass der systematische Fehler für den Datensatz der Forschungsfahrt gegen Null geht bei gleichzeitiger Reduzierung der Standardabweichungen der Differenzen von berechneter und gemessener Einstrahlung. Eine Überprüfung der modifizierten Strahlungsparametrisierung mit einem Datensatz der Nordseeinsel Sylt bestätigt diese positiven Resultate

Der Einfluss von Wolken auf den Strahlungsantrieb der Erde

The aim of this study is to estimate radiative budgets and radiative effects by clouds onto the radiation balance of the earth. The estimation was performed at the surface, the top of the atmosphere and for the atmospheric column. In addition, the surface radiative fluxes have been simulated by the single column model ECHAM5. The robust data base of the radiative measurements was set up along five cruises of the icebreaker POLARSTERN and the corresponding satellite remote sensing by MSG. A full sky imager for a rough offshore application was developed to derive the total cloud amount and the cloud type. Utilizing a microwave radiometer, the atmospheric temperature and humidity profiles as well as the liquid water path were measured continuously. The surface net budget is dominated by the solar radiative component with a mean value of 144W/m2, whereas the solar impact is high for cirrus and low for stratus. At the top of the atmosphere the solar fluxes are predominantly within the daily net budgets at tropical latitudes. This results in a radiative forcing of 37W/m2. The atmospheric column shows a strong thermal emittance and a slight solar absorption. Its net heat loss amounts to a total of −100W/m2. The strongest surface cloud longwave effectswere determined in the presence of low level clouds. Clouds with a high optical density induce strong negative solar effects when the solar altitude is high. The mean surface net effect is −34W/m2. For the purpose of calculating the mean surface net effect, a new parametrization was created, considering the total cloud amount and the solar zenith angle. At the top of the atmosphere the clear sky radiative fluxes are approached inaccurately. The average atmospheric cloud effect is −3W/m2. Cirrus clouds have little atmospheric solar effects and strong longwave effects, thus cirrus is the only cloud type causing a heating of the climate. The atmospheric longwave effects are highly negative for optical thick low level clouds. Mean atmospheric solar effects are positive for each cloud type. The atmospheric net effect is −4W/m2. Based on ECHAM5 simulations, the surface solar effects are about 20W/m2 higher than the measured effects. Surface longwave effects are simulated well. Under existence of cirrus and stratus the model physics with its single cloud layer works exactly. The surface solar effects of convective clouds, especially stratocumulus, show a large overestimation of up to 120W/m2

Shortwave surface radiation network for observing small-scale cloud inhomogeneity fields

As part of the High Definition Clouds and Precipitation for advancing Climate Prediction Observational Prototype Experiment (HOPE), a high-density network of 99 silicon photodiode pyranometers was set up around Jülich (10 km × 12 km area) from April to July 2013 to capture the small-scale variability of cloud-induced radiation fields at the surface. In this paper, we provide the details of this unique setup of the pyranometer network, data processing, quality control, and uncertainty assessment under variable conditions. Some exemplary days with clear, broken cloudy, and overcast skies were explored to assess the spatiotemporal observations from the network along with other collocated radiation and sky imager measurements available during the HOPE period

Radiative effects of the cloudy atmosphere from ground and satellite based observations

The radiation budget from surface observations and parameterizations is combined with that from satellite observations along the cruise tracks of the German icebreaker POLARSTERN in the North and South Atlantic under tropical, subtropical and mid-latitude conditions. Between 2008 and 2010 The German Leibniz-network OCEANET participated in six transfers from or to Bremerhaven, Germany to or from Punta Arenas, Southern Chile or Cape Town, South Africa. The present chapter introduces exemplarily the atmospheric measurements and resulting radiation products. The following properties are derived: Standard meteorological data, broadband downward solar and thermal irradiances, underwater profiles of spectral irradiance, latent and sensible heat fluxes, humidity and temperature profiles, water vapour and liquid water path, aerosol optical thickness and vertical profiles of aerosol optical thickness, cloud cover and cloud type. Cloud radiative effects at the surface have been determined for different marine cloud types. Together with top-of-atmosphere radiation fluxes from the SEVIRI radiometer onboard METEOSAT, the effect of clouds on atmospheric heating or cooling have been determined. The resulting cloud/radiation correlations will help to quantify the effects of clouds on the surface, ToA- and atmospheric radiation budget and to evaluate the ability of climate models to simulate these effects

Measured and Parameterized Energy Fluxes estimated for Atlantic Transects of R/V Polarstern

Sensible and latent heat fluxes were estimated from turbulence measurements gathered during several Atlantic transects of the R/V Polarstern. The inertial dissipation method was used to analyze the data. Resulting bulk transfer coefficients were then applied to the data from the ship’s meteorological system to get continuous time series of the heat fluxes. Combined to the measured downward solar and longwave radiation fluxes allows for an estimate of the total energy budget at the air-sea interface. Comparing these parameterized energy fluxes to ones based on the COARE 3.0 bulk flux algorithm show very strong agreement

G93-1145 Management of the Army Cutworm and Pale Western Cutworm

This NebGuide describes the life cycle of the army cutworm and pale western cutworm, and provides recommendations for management.The army cutworm, Euxoa auxiliaris, and the pale western cutworm, Agrotis orthogonia, are sporadic pests that are distributed throughout the Great Plains. The army cutworm can be found throughout Nebraska, but is more common in the western half of the state. Because of the drier environment, the pale western cutworm is found only in the western third of Nebraska. Both cutworms can feed on a vast array of crops and weeds. Their major economic impact is limited to winter wheat and alfalfa, because these are the vulnerable crops growing in the early spring when larval feeding activity occurs. However, they can also cause substantial damage to early spring row crops (sugarbeets and corn), especially in areas where winter cereal cover crops are used