Retrieval of Optical and Microphysical Cloud Properties Using Ship-based Spectral Solar Radiation Measurements over the Atlantic Ocean

In this thesis spectral solar zenith radiances are analyzed which were obtained from ship-based measurements over the Atlantic ocean. In combination with high-resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity-based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds. A statistical analysis of retrieved cloud properties during three Atlantic transects is introduced. Similar characteristics of cloud properties are found in the mid latitudes and northern subtropics but the large variability of meridional distribution in the remaining regions imply the prevailing influence of weather systems compared to typical cloud distributions. With about 63% homogeneous stratocumulus clouds are found to be the prevailing cloud type over ocean, while scattered and inhomogeneous liquid water clouds amount to 16% and 21%, respectively. All analyzed distributions are affected by an increased frequency of small values of cloud properties caused by 3D radiative effects. The comparison with satellite-based and ship-based cloud retrievals along the cruise track show comparable results for the cloud optical thickness with limitations for thick liquid water clouds. The meridional distribution of effective radius agreed within the uncertainties of both methods, however, the satellite-derived values are biased toward larger mean values

Comparison of a Backscatter LIDAR during LICL 2009

In May 2009 the European Aerosol Research Lidar Network (EARLINET) started an intercomparison campaign took place in Leipzig, Germany. The main objective was to compare the mobile Earlinet-LIDARs to have characteristically reference systems and to ensure permanent qualitative Measurements. To test the LIDAR of the Leipziger Institute for Meteorology (LIM) measurements during the comparison time periods were performed and compared to two EARLINET – LIDARs. The main objective was to compare the range-corrected total signal as well as backscatter and extinction coefficients to get information of the accuracy of the system for further independent measurements in the future. It will be shown that the ALS300 is able to achieve results which are in agreement to other lidar systems. However the deviation to the other Lidars depends strongly on the background radiation so that there is a smaller deviation of the mean signal during nighttime measurements then daytime measurements

Retrieval of optical and microphysical cloud properties using shipbased spectral solar radiation measurements over the Atlantic ocean

In this paper spectral solar zenith radiances are analyzed which were obtained from ship–based measurements over the Atlantic ocean. In combination with high–resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity–based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds.In dem vorliegenden Artikel werden abwärtsgerichtete spektrale Strahldichten analysiert, die mithilfe schiffsgebundener Beobachtungen über dem Atlantischen Ozean gemessen wurden. In Verbindung mit hochauflösenden Lidar und Mikrowellenradiometer Fernerkundungsverfahren werden optische und mikrophysikalische Wolkeneigenschaften aus spektralen Daten abgeleitet. Um Probleme bereits existierender Verfahren, die auf Transmissionen basieren, zu beseitigen, wird ein neuer Fernerkundungsalgorithmus vorgestellt, der nicht nur Zweideutigkeiten in der Bestimmung der Parameter umgeht, sondern auch den Einfluss von Messunsicherheiten verringert. Die Methode vergleicht gemessene spektrale Transmissionsverhältnisse bei sechs Wellenlängen mit modellierten Verhältnissen. Die neue Fernerkundungsmethode ist schnell und exakt, sodass sie für operative Zwecke geeignet ist. Sie wird für homogene und inhomogene Wasserwolken als auch für Cirren angewendet. Die Ergebnisse des neuen Ableitungsverfahrens werden mit Beobachtungen des Flüssigwasserpfades eines Mikrowellenradiometers verglichen. Daraus ergibt sich eine Überschätzung des Flüssigwasserpfades unter dicken Wolken, jedoch eine leichte Unterschätzung für dünne Wolken

Introduction of the Transregional Collaborative Research Center TR 172: Arctic Amplification

A new German research consortium is investigating the causes and effects of the rapid rise of near-surface air temperatures in the Artic. Within the last 25 years a remarkable increase of the Arctic near-surface air temperature exceeding the global warming by a factor of two to three has been observed. The phenomenon is commonly referred to as Arctic Amplification. The warming results in rather drastic changes of a variety of climate parameters. For example, the Arctic sea ice has declined significantly. This ice retreat has been well identified by satellite measurements. However, coupled regional and global climate models still fail to reproduce it adequately; they tend to systematically underestimate the observed sea ice decline. This model observation difference implies that the underlying physical processes and feedback mechanisms are not appropriately represented in Arctic climate models. Thus, the predictions of these models are also likely to be inadequate. It is mandatory to identify the origin of this disagreement.Ein neu geschaffenes deutsches Forschungskonsortium untersucht die Ursachen und Effekte des rapiden Anstiegs der bodennahen Lufttemperatur in der Arktis. Innerhalb der letzten 25 Jahre wurde ein bemerkenswerter Anstieg der Bodenlufttemperatur in der Arktis beobachtet, welcher die globale Erwärmung um den Faktor 2 bis 3 übersteigt. Dieses Phänomen wird als arktische Verstärkung bezeichnet. Diese Erwärmung resultiert vielmehr in einer drastischen Änderung einer Vielzahl von Klimarparametern. Beispielsweise ist das arktische Meereis deutlich zurückgegangen. Dieser Eisrückgang wurde durch Satellitenbeobachtungen gut beobachtet. Dagegen haben regionale und globale Klimamodelle immer noch Probleme, den Rückgang entsprechend zu reproduzieren. Sie tendieren dazu, den Meereisrückgang systematisch zu unterschätzen. Die Unterschiede zwischen Modell und Beobachtungen legen nahe, dass die grundlegenden physikalischen Prozesse und Rückkopplungsmechanismen nicht entsprechend in arktischen Klimamodellen repräsentiert werden. Somit sind wahrscheinlich auch die Vorhersagen der Modelle unzureichend. Es ist notwendig, den Ursprung dieser Unstimmigkeit zu identifizieren

Retrieval of optical and microphysical cloud properties using shipbased spectral solar radiation measurements over the Atlantic ocean

In this paper spectral solar zenith radiances are analyzed which were obtained from ship–based measurements over the Atlantic ocean. In combination with high–resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity–based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds.In dem vorliegenden Artikel werden abwärtsgerichtete spektrale Strahldichten analysiert, die mithilfe schiffsgebundener Beobachtungen über dem Atlantischen Ozean gemessen wurden. In Verbindung mit hochauflösenden Lidar und Mikrowellenradiometer Fernerkundungsverfahren werden optische und mikrophysikalische Wolkeneigenschaften aus spektralen Daten abgeleitet. Um Probleme bereits existierender Verfahren, die auf Transmissionen basieren, zu beseitigen, wird ein neuer Fernerkundungsalgorithmus vorgestellt, der nicht nur Zweideutigkeiten in der Bestimmung der Parameter umgeht, sondern auch den Einfluss von Messunsicherheiten verringert. Die Methode vergleicht gemessene spektrale Transmissionsverhältnisse bei sechs Wellenlängen mit modellierten Verhältnissen. Die neue Fernerkundungsmethode ist schnell und exakt, sodass sie für operative Zwecke geeignet ist. Sie wird für homogene und inhomogene Wasserwolken als auch für Cirren angewendet. Die Ergebnisse des neuen Ableitungsverfahrens werden mit Beobachtungen des Flüssigwasserpfades eines Mikrowellenradiometers verglichen. Daraus ergibt sich eine Überschätzung des Flüssigwasserpfades unter dicken Wolken, jedoch eine leichte Unterschätzung für dünne Wolken

Retrieval of Optical and Microphysical Cloud Properties Using Ship-based Spectral Solar Radiation Measurements over the Atlantic Ocean

In this thesis spectral solar zenith radiances are analyzed which were obtained from ship-based measurements over the Atlantic ocean. In combination with high-resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity-based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds. A statistical analysis of retrieved cloud properties during three Atlantic transects is introduced. Similar characteristics of cloud properties are found in the mid latitudes and northern subtropics but the large variability of meridional distribution in the remaining regions imply the prevailing influence of weather systems compared to typical cloud distributions. With about 63% homogeneous stratocumulus clouds are found to be the prevailing cloud type over ocean, while scattered and inhomogeneous liquid water clouds amount to 16% and 21%, respectively. All analyzed distributions are affected by an increased frequency of small values of cloud properties caused by 3D radiative effects. The comparison with satellite-based and ship-based cloud retrievals along the cruise track show comparable results for the cloud optical thickness with limitations for thick liquid water clouds. The meridional distribution of effective radius agreed within the uncertainties of both methods, however, the satellite-derived values are biased toward larger mean values

Retrieval of Optical and Microphysical Cloud Properties Using Ship-based Spectral Solar Radiation Measurements over the Atlantic Ocean

In this thesis spectral solar zenith radiances are analyzed which were obtained from ship-based measurements over the Atlantic ocean. In combination with high-resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity-based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds. A statistical analysis of retrieved cloud properties during three Atlantic transects is introduced. Similar characteristics of cloud properties are found in the mid latitudes and northern subtropics but the large variability of meridional distribution in the remaining regions imply the prevailing influence of weather systems compared to typical cloud distributions. With about 63% homogeneous stratocumulus clouds are found to be the prevailing cloud type over ocean, while scattered and inhomogeneous liquid water clouds amount to 16% and 21%, respectively. All analyzed distributions are affected by an increased frequency of small values of cloud properties caused by 3D radiative effects. The comparison with satellite-based and ship-based cloud retrievals along the cruise track show comparable results for the cloud optical thickness with limitations for thick liquid water clouds. The meridional distribution of effective radius agreed within the uncertainties of both methods, however, the satellite-derived values are biased toward larger mean values

Retrieval of optical and microphysical cloud properties using shipbased spectral solar radiation measurements over the Atlantic ocean

In this paper spectral solar zenith radiances are analyzed which were obtained from ship–based measurements over the Atlantic ocean. In combination with high–resolution lidar and microwave remote sensing optical and microphysical cloud properties were retrieved using spectral radiation data. To overcome problems of existing transmissivity–based cloud retrievals, a new retrieval algorithm is introduced which circumvents retrieval ambiguities and reduces the influence of measurement uncertainties. The method matches radiation measurements of ratios of spectral transmissivity at six wavelengths with modeled transmissivities. The new retrieval method is fast and accurate, and thus suitable for operational purposes. It is applied to homogeneous and inhomogeneous liquid water and cirrus clouds. The results from the new algorithm are compared to observations of liquid water path obtained from a microwave radiometer, yielding an overestimation for thick liquid water clouds but a slight underestimation for thin clouds.In dem vorliegenden Artikel werden abwärtsgerichtete spektrale Strahldichten analysiert, die mithilfe schiffsgebundener Beobachtungen über dem Atlantischen Ozean gemessen wurden. In Verbindung mit hochauflösenden Lidar und Mikrowellenradiometer Fernerkundungsverfahren werden optische und mikrophysikalische Wolkeneigenschaften aus spektralen Daten abgeleitet. Um Probleme bereits existierender Verfahren, die auf Transmissionen basieren, zu beseitigen, wird ein neuer Fernerkundungsalgorithmus vorgestellt, der nicht nur Zweideutigkeiten in der Bestimmung der Parameter umgeht, sondern auch den Einfluss von Messunsicherheiten verringert. Die Methode vergleicht gemessene spektrale Transmissionsverhältnisse bei sechs Wellenlängen mit modellierten Verhältnissen. Die neue Fernerkundungsmethode ist schnell und exakt, sodass sie für operative Zwecke geeignet ist. Sie wird für homogene und inhomogene Wasserwolken als auch für Cirren angewendet. Die Ergebnisse des neuen Ableitungsverfahrens werden mit Beobachtungen des Flüssigwasserpfades eines Mikrowellenradiometers verglichen. Daraus ergibt sich eine Überschätzung des Flüssigwasserpfades unter dicken Wolken, jedoch eine leichte Unterschätzung für dünne Wolken

Comparison of a Backscatter LIDAR during LICL 2009

In May 2009 the European Aerosol Research Lidar Network (EARLINET) started an intercomparison campaign took place in Leipzig, Germany. The main objective was to compare the mobile Earlinet-LIDARs to have characteristically reference systems and to ensure permanent qualitative Measurements. To test the LIDAR of the Leipziger Institute for Meteorology (LIM) measurements during the comparison time periods were performed and compared to two EARLINET – LIDARs. The main objective was to compare the range-corrected total signal as well as backscatter and extinction coefficients to get information of the accuracy of the system for further independent measurements in the future. It will be shown that the ALS300 is able to achieve results which are in agreement to other lidar systems. However the deviation to the other Lidars depends strongly on the background radiation so that there is a smaller deviation of the mean signal during nighttime measurements then daytime measurements

Comparison of a Backscatter LIDAR during LICL 2009

In May 2009 the European Aerosol Research Lidar Network (EARLINET) started an intercomparison campaign took place in Leipzig, Germany. The main objective was to compare the mobile Earlinet-LIDARs to have characteristically reference systems and to ensure permanent qualitative Measurements. To test the LIDAR of the Leipziger Institute for Meteorology (LIM) measurements during the comparison time periods were performed and compared to two EARLINET – LIDARs. The main objective was to compare the range-corrected total signal as well as backscatter and extinction coefficients to get information of the accuracy of the system for further independent measurements in the future. It will be shown that the ALS300 is able to achieve results which are in agreement to other lidar systems. However the deviation to the other Lidars depends strongly on the background radiation so that there is a smaller deviation of the mean signal during nighttime measurements then daytime measurements