[1] We compared 1 year of Advanced Microwave Scanning Radiometer-EOS (AMSR-E) Wentz and Moderate Resolution Imaging Spectroradiometer (MODIS) cloud liquid water path estimates in warm marine clouds. In broken scenes AMSR-E increasingly overestimated MODIS, and retrievals became uncorrelated as cloud fraction decreased, while in overcast scenes the techniques showed generally better agreement, but with a MODIS overestimation. We found microwave and visible near-infrared retrievals being most consistent in extensive marine Sc clouds with correlations up to 0.95 and typical RMS differences of 15 g m −2 . The overall MODIS high bias in overcast domains could be removed, in a global mean sense, by adiabatic correction; however, large regional differences remained. Most notably, MODIS showed strong overestimations at high latitudes, which we traced to 3-D effects in plane-parallel visible-near-infrared retrievals over heterogeneous clouds at low Sun. In the tropics or subtropics, AMSR-E-MODIS differences also depended on cloud type, with MODIS overestimating in stratiform clouds and underestimating in cumuliform clouds, resulting in large-scale coherent bias patterns where marine Sc transitioned into trade wind Cu. We noted similar geographic variations in Wentz cloud temperature errors and MODIS 1.6-3.7 mm droplet effective radius differences, suggesting that microwave retrieval errors due to cloud absorption uncertainties, and visible near-infrared retrieval errors due to cloud vertical stratification might have contributed to the observed liquid water path bias patterns. Finally, cloud-rain partitioning was found to introduce a systematic low bias in Wentz retrievals above 180 g m −2 as the microwave algorithm erroneously assigned an increasing portion of the liquid water content of thicker nonprecipitating clouds to rain.

Abstract. A correct and reliable forecast of volcanic plume dispersion is vital for aviation safety. This can only be achieved by representing all responsible physical and chemical processes (sources, sinks, and interactions) in the forecast models. The representation of the sources has been enhanced over the last decade, while the sinks and interactions have received less attention. In particular, aerosol dynamic processes and aerosol–radiation interaction are neglected so far. Here we address this gap by further developing the ICON-ART (ICOsahedral Nonhydrostatic – Aerosols and Reactive Trace gases) global modeling system to account for these processes. We use this extended model for the simulation of volcanic aerosol dispersion after the Raikoke eruption in June 2019. Additionally, we validate the simulation results with measurements from AHI (Advanced Himawari Imager), CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization), and OMPS-LP (Ozone Mapping and Profiling Suite-Limb Profiler). Our results show that around 50 % of very fine volcanic ash mass (particles with diameter d<30 µm) is removed due to particle growth and aging. Furthermore, the maximum volcanic cloud top height rises more than 6 km over the course of 4 d after the eruption due to aerosol–radiation interaction. This is the first direct evidence that shows how cumulative effects of aerosol dynamics and aerosol–radiation interaction lead to a more precise forecast of very fine ash lifetime in volcanic clouds.

Stereo methods using GOES‐17 and Himawari‐8 applied to the Hunga Tonga‐Hunga Ha'apai volcanic plume on 15 January 2022 show overshooting tops reaching 50–55 km altitude, a record in the satellite era. Plume height is important to understand dispersal and transport in the stratosphere and climate impacts. Stereo methods, using geostationary satellite pairs, offer the ability to accurately capture the evolution of plume top morphology quasi‐continuously over long periods. Manual photogrammetry estimates plume height during the most dynamic early phase of the eruption and a fully automated algorithm retrieves both plume height and advection every 10 min during a more frequently sampled and stable phase beginning 3 hr after the eruption. Stereo heights are confirmed with Global Navigation Satellite System Radio Occultation bending angles, showing that much of the plume was lofted 30–40 km into the atmosphere. Cold bubbles are observed in the stratosphere with brightness temperature of ∼173 K.

This study identifies meteorological variables that control the macrophysical properties of shallow cumulus cloud fields over the tropical ocean. We use 1,158 high‐resolution Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) images to derive properties of shallow cumuli, such as their size distribution, cloud top heights, fractal dimensions, and spatial organization, as well as cloud amount. The large‐scale meteorology is characterized by the lower‐tropospheric stability, subsidence rate, sea surface temperature, total column water vapor, wind speed, wind shear, and Bowen ratio. The surface wind speed emerges as the most powerful control factor. With increasing wind speed the cloud amount and cloud top heights show a robust increase accompanied by a marked shift in the cloud size distribution toward larger clouds with smoother shapes. These results lend observational support to the deepening response of a wind‐driven marine boundary layer as simulated by large‐eddy models. The other control factors cause smaller changes in the cloud field properties. We find a robust increase in cloud amount with increasing stability and decreasing sea surface temperature, respectively, which confirms a well‐known behavior of marine stratocumulus also for shallow cumulus clouds. Due to the high resolution of cloud images, we are able to study the lower end of the cloud size distribution and find a robust double power law behavior with a scale break at 590 m. We find a variation in the shape of the cloud size distribution with Bowen ratio, qualitatively consistent with modeling results and suggesting the Bowen ratio as a new potential control factor on shallow cumulus clouds.

Satellite wind measurements represent an invaluable contribution to the description of the flow field over the oceans. Conventional cloud-tracking techniques suffer from the inability to simultaneously determine wind speed and height. Currently, the uncertainty in the independently calculated heights is the major factor limiting the accuracy of cloud motion winds. Near-simultaneous multiangle imagery from the multiangle imaging spectroradiometer (MISR) forms the basis of a unique method able to simultaneously retrieve cloud motion and height. The coupled motion and height parallaxes can be unscrambled from three properly selected multiangle views through a purely geometric, stereoscopic approach. Results based on simulated data indicate that for a mesoscale domain the average along-track and cross-track horizontal wind components may be obtained with an accuracy as good as 3-4 m s Ϫ1 , and 1-2 m s Ϫ1 , respectively, and with a corresponding height error of 300-400 m. The technique also possesses a limited capability to distinguish between low and high features moving at different velocities in a multilayer cloud field.

[1] This study investigated the consistency between microwave and optical water path estimates of oceanic clouds from Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI), Moderate Resolution Imaging Spectroradiometer (MODIS), and Multiangle Imaging Spectroradiometer (MISR). We used microwave estimates from the Wentz algorithm for warm, nonprecipitating clouds and both Wentz retrievals and standard TMI profiles for cold, precipitating clouds. Optical estimates were derived from cloud optical thickness and particle effective radius. For warm, nonprecipitating clouds the two methods showed good agreement at the 25-km resolution of the microwave measurements, with liquid water path means being within 5-10%, an overall correlation of 0.85, and RMS difference of $25 g m À2 . Multiangle optical retrievals showed only weak variations with view zenith angle, building further confidence in the results. An error analysis suggested that optical estimates were more certain than microwave ones, primarily because 1-D plane-parallel radiative transfer seemed to apply well at the coarser comparison scales. However, there appeared to be a slight but systematic dependence on cloud amount as microwave retrievals increasingly overestimated optical ones at cloud fractions below $65%. For cold, precipitating clouds we tested three common interpretations of optical retrievals: liquid water path, ice water path, and total water path. The relationship between microwave and optical estimates was weak in all cases, with correlations no more than 0.5, and RMS differences at least an order of magnitude larger than for warm clouds. The weakest correlation (0.37) was found when optical retrievals were interpreted as ice water paths. If anything, optical estimates appeared best correlated with microwave cloud liquid water paths.

The operational retrieval of height-resolved cloud motion vectors by the Multiangle Imaging Spectro Radiometer on the Terra satellite has been significantly improved by using sub-pixel approaches to coregistration and disparity assessment, and by imposing stronger quality control based on the agreement between independent forward and aft triplet retrievals. Analysis of the fore-aft differences indicates that CMVs pass the basic operational quality control 67% of the time, with rms differences --in speed of 2.4 d s , in direction of 17", and in height assignment of 290 m. The use of enhanced quality control thresholds reduces these rms values to 1.5 d s , 17" and 165 m, respectively, at the cost of reduced coverage to 45%. Use of the enhanced thresholds also eliminates a tendency for the rms differences to increase with height. Comparison of CMVs from an earlier operational version that had slightly weaker quality control, with 6-hour forecast winds fiom the Global Modeling and Assimilation Office yielded very low bias values and an rms vector difference that ranged from 5 d s for low clouds to 1 0 d s for high clouds. Popular SummaryUnlike most satellite instruments, Multiangle Imaging SpectroRadiometer (MISR) on the Terra satellite is a new instrument that will image Earth's climate system simultaneously at 9 different angles. One camera points toward nadir, and the others provide forward and aftward view angles, at the Earth's surface, of 26.1", 45.6", 60.0", and 70.5". As the instrument flies overhead, each region of the Earth's surface is successively imaged by all nine cameras in each of four wavelengths (blue, green, red, and near-infrared).In addition to measure the amount of sunlight that is scattered in different directions, MISR can also distinguish different types of clouds, aerosol particles, and surfaces. With the information obtained from MISR in the amount, types, and heights of clouds and the distribution of land surface cover, the heightresolved cloud motion vectors (CMVs) can be retrieved.In this paper, we focused on improving operational retrieval algorithm of height-resolved CMVs. Subpixel approaches were used for co-registration and disparity assessment, and stronger quality control was imposed based on the agreement between independent forward and aft triplet retrievals. Analysis of the fore-aft differences indicated that CMVs passed the basic operational quality control 67% of the time, with rms differences --in speed of 2.4 d s , in direction of 17", and in height assignment of 290 m.The use of enhanced quality control thresholds reduced these rms values to 1.5 d s , 14" and 165 m, respectively, at the cost of reduced coverage to 45%. Use of the enhanced thresholds also eliminated a tendency for the rms differences to increase with height. Comparison of CMVs from an earlier operational version that had slightly weaker quality control, with 6-hour forecast winds from the Global Modeling and Assimilation Office yielded very low bias values and an rms vector difference that ranged fr...

We investigated the view angle dependence of domain mean Moderate Resolution Imaging Spectroradiometer (MODIS) liquid water path (LWP) and that of corresponding cloud optical thickness, effective radius, and liquid cloud fraction as proxy for plane-parallel retrieval biases. Independent Advanced Microwave Scanning Radiometer-EOS LWP was used to corroborate that the observed variations with sun-view geometry were not severely affected by seasonal/latitudinal changes in cloud properties. Microwave retrievals showed generally small (<10%) cross-swath variations. The view angle (cross-swath) dependence of MODIS optical thickness was weaker in backscatter than forward scatter directions and transitioned from mild ∩ shape to stronger ∪ shape as heterogeneity, sun angle, or latitude increased. The 2.2 μm effective radius variations always had a ∪ shape, which became pronounced and asymmetric toward forward scatter in the most heterogeneous clouds and/or at the lowest sun. Cloud fraction had the strongest and always ∪-shaped view angle dependence. As a result, in-cloud MODIS cloud liquid water path (CLWP) showed surprisingly good view angle (cross-swath) consistency, usually comparable to that of microwave retrievals, due to cancelation between optical thickness and effective radius biases. Larger (20-40%) nadir-relative increases were observed in the most extreme heterogeneity and sun angle bins, that is, typically in the polar regions, which, however, constituted only 3-8% of retrievals. The good consistency of MODIS in-cloud CLWP was lost for gridbox mean LWP, which was dominated by the strong cloud fraction increase with view angle. More worryingly, MODIS LWP exhibited significant and systematic absolute increases with heterogeneity and sun angle that is not present in microwave LWP.