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- Author or Editor: Linda Forster x
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Abstract
Estimates of the global radiative forcing (RF) of line-shaped contrails and contrail cirrus exhibit a high level of uncertainty. In most cases, 1D radiative models have been used to determine the RF on a global scale. In this paper the effect of neglecting the 3D radiative effects of realistic contrails is quantified. Calculating the 3D effects of an idealized elliptical contrail as in the work of Gounou and Hogan with the 3D radiative transfer model MYSTIC (for “Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres”) produced comparable results: as in Gounou and Hogan’s work the 3D effect (i.e., the difference in RF between a 3D calculation and a 1D approximation) on contrail RF was on the order of 10% in the longwave and shortwave. The net 3D effect, however, can be much larger, since the shortwave and longwave RF largely cancel during the day. For the investigation of the 3D effects of more realistic contrails, the microphysical input was provided by simulations of a 2D contrail-to-cirrus large-eddy simulation (LES) model. To capture some of the real variability in contrail properties, this paper examines two contrail evolutions from 20 min up to 6 h in an environment with either high or no vertical wind shear. This study reveals that the 3D effects show a high variability under realistic conditions since they depend strongly on the optical properties and the evolutionary state of the contrails. The differences are especially large for low elevations of the sun and contrails spreading in a sheared environment. Thus, a parameterization of the 3D effects in climate models would need to consider both geometry and microphysics of the contrail.
Abstract
Estimates of the global radiative forcing (RF) of line-shaped contrails and contrail cirrus exhibit a high level of uncertainty. In most cases, 1D radiative models have been used to determine the RF on a global scale. In this paper the effect of neglecting the 3D radiative effects of realistic contrails is quantified. Calculating the 3D effects of an idealized elliptical contrail as in the work of Gounou and Hogan with the 3D radiative transfer model MYSTIC (for “Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres”) produced comparable results: as in Gounou and Hogan’s work the 3D effect (i.e., the difference in RF between a 3D calculation and a 1D approximation) on contrail RF was on the order of 10% in the longwave and shortwave. The net 3D effect, however, can be much larger, since the shortwave and longwave RF largely cancel during the day. For the investigation of the 3D effects of more realistic contrails, the microphysical input was provided by simulations of a 2D contrail-to-cirrus large-eddy simulation (LES) model. To capture some of the real variability in contrail properties, this paper examines two contrail evolutions from 20 min up to 6 h in an environment with either high or no vertical wind shear. This study reveals that the 3D effects show a high variability under realistic conditions since they depend strongly on the optical properties and the evolutionary state of the contrails. The differences are especially large for low elevations of the sun and contrails spreading in a sheared environment. Thus, a parameterization of the 3D effects in climate models would need to consider both geometry and microphysics of the contrail.
Abstract
For passive satellite imagers, current retrievals of cloud optical thickness and effective particle size fail for convective clouds with 3D morphology. Indeed, being based on 1D radiative transfer (RT) theory, they work well only for horizontally homogeneous clouds. A promising approach for treating clouds as fully 3D objects is cloud tomography, which has been demonstrated for airborne observations. However, more efficient forward 3D RT solvers are required for cloud tomography from space. Here, we present a path forward by acknowledging that optically thick clouds have “veiled cores” (VCs). Sunlight scattered into and out of this deep region does not contribute significant information about the inner structure of the cloud to the spatially detailed imagery. We investigate the VC location for the MISR and MODIS imagers. While MISR provides multiangle imagery in the visible and near-infrared (IR), MODIS includes channels in the shortwave IR, albeit at a single view angle. This combination will enable future 3D retrievals to disentangle the cloud’s effective particle size and extinction fields. We find that, in practice, the VC is located at an optical distance of ~5, starting from the cloud boundary along the line of sight. For MODIS’s absorbing wavelengths the VC covers a larger volume, starting at smaller optical distances. This concept will not only lead to a reduction in the number of unknowns for the tomographic reconstruction but also significantly increase the speed and efficiency of the 3D RT solver at the heart of the algorithm by applying, say, the photon diffusion approximation inside the VC.
Abstract
For passive satellite imagers, current retrievals of cloud optical thickness and effective particle size fail for convective clouds with 3D morphology. Indeed, being based on 1D radiative transfer (RT) theory, they work well only for horizontally homogeneous clouds. A promising approach for treating clouds as fully 3D objects is cloud tomography, which has been demonstrated for airborne observations. However, more efficient forward 3D RT solvers are required for cloud tomography from space. Here, we present a path forward by acknowledging that optically thick clouds have “veiled cores” (VCs). Sunlight scattered into and out of this deep region does not contribute significant information about the inner structure of the cloud to the spatially detailed imagery. We investigate the VC location for the MISR and MODIS imagers. While MISR provides multiangle imagery in the visible and near-infrared (IR), MODIS includes channels in the shortwave IR, albeit at a single view angle. This combination will enable future 3D retrievals to disentangle the cloud’s effective particle size and extinction fields. We find that, in practice, the VC is located at an optical distance of ~5, starting from the cloud boundary along the line of sight. For MODIS’s absorbing wavelengths the VC covers a larger volume, starting at smaller optical distances. This concept will not only lead to a reduction in the number of unknowns for the tomographic reconstruction but also significantly increase the speed and efficiency of the 3D RT solver at the heart of the algorithm by applying, say, the photon diffusion approximation inside the VC.
Abstract
To address critical gaps identified by the National Academies of Sciences, Engineering, and Medicine in the current Earth system observation strategy, the 2017–27 Decadal Survey for Earth Science and Applications from Space recommended incubating concepts for future targeted observables including the atmospheric planetary boundary layer (PBL). A subsequent NASA PBL Incubation Study Team Report identified measurement requirements and activities for advancing the maturity of the technologies applicable to the PBL targeted observables and their associated science and applications priorities. While the PBL is the critical layer where humans live and surface energy, moisture, and mass exchanges drive the Earth system, it is also the farthest and most inaccessible layer for spaceborne instruments. Here we document a PBL retrieval observing system simulation experiment (OSSE) framework suitable for assessing existing and new measurement techniques and determining their accuracy and improvements needed for addressing the elevated Decadal Survey requirements. In particular, the benefits of large-eddy simulation (LES) are emphasized as a key source of high-resolution synthetic observations for key PBL regimes: from the tropics, through subtropics and midlatitudes, to subpolar and polar regions. The potential of LES-based PBL retrieval OSSEs is explored using six instrument simulators: Global Navigation Satellite System–Radio Occultation, differential absorption radar, visible to shortwave infrared spectrometer, infrared sounder, Multi-angle Imaging SpectroRadiometer, and microwave sounder. The crucial role of LES in PBL retrieval OSSEs and some perspectives for instrument developments are discussed.
Abstract
To address critical gaps identified by the National Academies of Sciences, Engineering, and Medicine in the current Earth system observation strategy, the 2017–27 Decadal Survey for Earth Science and Applications from Space recommended incubating concepts for future targeted observables including the atmospheric planetary boundary layer (PBL). A subsequent NASA PBL Incubation Study Team Report identified measurement requirements and activities for advancing the maturity of the technologies applicable to the PBL targeted observables and their associated science and applications priorities. While the PBL is the critical layer where humans live and surface energy, moisture, and mass exchanges drive the Earth system, it is also the farthest and most inaccessible layer for spaceborne instruments. Here we document a PBL retrieval observing system simulation experiment (OSSE) framework suitable for assessing existing and new measurement techniques and determining their accuracy and improvements needed for addressing the elevated Decadal Survey requirements. In particular, the benefits of large-eddy simulation (LES) are emphasized as a key source of high-resolution synthetic observations for key PBL regimes: from the tropics, through subtropics and midlatitudes, to subpolar and polar regions. The potential of LES-based PBL retrieval OSSEs is explored using six instrument simulators: Global Navigation Satellite System–Radio Occultation, differential absorption radar, visible to shortwave infrared spectrometer, infrared sounder, Multi-angle Imaging SpectroRadiometer, and microwave sounder. The crucial role of LES in PBL retrieval OSSEs and some perspectives for instrument developments are discussed.
Abstract
The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.
Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.
In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather.
Abstract
The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.
Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.
In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather.
