The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific

The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40° S to the equator and from 110° W to 70° W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing geographic patterns of mean cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85° W 20° S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa

Synergy of Multiple Satellite Observations in the Study of Cloud Thermodynamics of Tropical Deep Convection.

Tropical convection lies at the heart of atmospheric research, especially for global weather and climate predictions; satellite measurements with large spatial coverage provide valuable information to deepen and broaden our scientific understandings of this subject. This thesis is motivated to utilize satellite measurements with assistance of modeling tools in a synergistic way to study tropical deep convection. First a generic parallax correction method is proposed to remove the biases resulting from the mismatch of satellite footprints due to different sensor viewing angles targeting the same object. Second a non-blackbody correction is proposed to better estimate cloud top temperature utilizing the vertical structure within the cloud top layer probed by CloudSat and CALIPSO. The distance between the physical cloud top and the effective emission level is shown to have a linear dependence on cloud top fuzziness (CTF; difference between cloud top and 10dBz radar echo) when CTF is less than ~2km. Beyond this threshold, the effective emission level remains 0.74km below the cloud top due to the saturation of IR absorption and emission. This relationship clearly improves simulated MODIS radiances comparing with the observed counterparts. The distribution of cloud top buoyancy for tropical deep convections derived using cloud top and ambient condition indicates that convective development is sensitive to both land-ocean contrast and diurnal cycle. Under certain assumptions, vertical velocity inside the convective core is derived and the result is consistent with typical vertical velocity profiles observed by air-bone Doppler radars for tropical deep convections, such as the altitude for the maximum vertical velocity and the existence of a weak detrainment layer in the mid-troposphere. GCM simulations indicate that overshooting deep convection could be responsible for the vertical transport of black carbon into the stratosphere especially over the India subcontinent during South Asia summer monsoon, and that black carbon in the stratosphere is transported upward at as large as twice the speed of water vapor transport. To explore a possible observational strategy for such injection of black carbon into the stratosphere, a limb-view infrared detection method is proposed based on forward modeling of radiative transfer and the simulated profiles.PhDAtmospheric, Oceanic and Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109016/1/cpwang_1.pd

A search for large-scale effects of ship emissions on clouds and radiation in satellite data

Ship tracks are regarded as the most obvious manifestations of the effect of anthropogenic aerosol particles on clouds (indirect effect). However, it is not yet fully quantified whether there are climatically relevant effects on large scales beyond the narrow ship tracks visible in selected satellite images. A combination of satellite and reanalysis data is used here to analyze regions in which major shipping lanes cut through otherwise pristine marine environments in subtropical and tropical oceans. We expect the region downwind of a shipping lane is affected by the aerosol produced by shipping emissions but not the one upwind. Thus, differences in microphysical and macrophysical cloud properties are analyzed statistically. We investigate microphysical and macrophysical cloud properties as well as the aerosol optical depth and its fine-mode fraction for the years 2005–2007 as provided for by retrievals of the two Moderate Resolution Imaging Spectroradiometer instruments. Water-cloud properties include cloud optical depth, cloud droplet effective radius, cloud top temperature, and cloud top pressure. Large-scale meteorological parameters are taken from ERA-Interim reanalysis data and microwave remote sensing (sea surface temperature). We analyze the regions of interest in a Eulerian and Lagrangian sense, i.e., sampling along shipping lanes and sampling along wind trajectories, respectively. No statistically significant impacts of shipping emissions on large-scale cloud fields could be found in any of the selected regions close to major shipping lanes. In conclusion, the net indirect effects of aerosols from ship emissions are not large enough to be distinguishable from the natural dynamics controlling cloud presence and formation

Advances and Limitations of Atmospheric Boundary Layer Observations with GPS Occultation over Southeast Pacific Ocean

The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific Ocean is featured with a strong temperature inversion and a sharp moisture gradient across the ABL top. The strong moisture and temperature gradients result in a sharp refractivity gradient that can be precisely detected by the Global Positioning System (GPS) radio occultation (RO) measurements. In this paper, the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect a wide range of ABL height variations (1-2 kilometer) as observed from the radiosondes. However, the ECMWF analysis systematically underestimates the ABL heights. The sharp refractivity gradient at the ABL top frequently exceeds the critical refraction (e.g., 157 N-unit per kilometer) and becomes the so-called ducting condition, which results in a systematic RO refractivity bias (or called N-bias) inside the ABL. Simulation study based on radiosonde profiles reveals the magnitudes of the N-biases are vertical resolution dependent. The N-bias is also the primary cause of the systematically smaller refractivity gradient (rarely exceeding 110 N-unit per kilometer) at the ABL top from RO measurement. However, the N-bias seems not affect the ABL height detection. Instead, the very large RO bending angle and the sharp refractivity gradient due to ducting allow reliable detection of the ABL height from GPS RO. The seasonal mean climatology of ABL heights derived from a nine-month composite of COSMIC RO soundings over the SE Pacific reveals significant differences from the ECMWF analysis. Both show an increase of ABL height from the shallow stratocumulus near the coast to a much higher trade wind inversion further off the coast. However, COSMIC RO shows an overall deeper ABL and reveals different locations of the minimum and maximum ABL heights as compared to the ECMWF analysis. At low latitudes, despite the decreasing number of COSMIC RO soundings and the lower percentage of soundings that penetrate into the lowest 500-m above the mean-sea-level, there are small sampling errors in the mean ABL height climatology. The difference of ABL height climatology between COSMIC RO and ECMWF analysis over SE Pacific is significant and requires further studies

A Global Investigation Of Cloud-Radiative Properties Through An Integrative Analysis Of Observations And Model Simulations

The cloud and radiative properties simulated in an assortment of global climate models (GCMs) and reanalyses are examined to identify and assess systematic biases based upon comparisons with multiple satellites observations and retrievals. The global mean total column cloud fraction (CF) simulated by the 33-member multimodel mean is 7% and 17% lower than the results from passive (Moderate Resolution Infrared Spectroradiometer, MODIS) and active (CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, CALIPSO) satellite remote sensing platforms. The simulated cloud water path (CWP), which is used as a proxy for optical depth, on global average, has a negative bias of ~17 g mâ2. Despite these errors in simulated cloud properties, the simulated top-of-atmosphere (TOA) radiation budgets match relatively well with Clouds and the Earth Radiant Energy System (CERES) measurements. The biases in multimodel mean global TOA reflected shortwave (SW) and outgoing longwave (LW) fluxes and cloud radiative effects (CREs) are less than 2.5 W mâ2. Nevertheless, when assessing models individually, some physically inconsistent results are evident. For example, in the ACCESS1.0 model, the simulated TOA SW and LW fluxes are within 2 W mâ2 of the observed global means, however, the global mean CF and CWP are underpredicted by ~10% and ~25 g mâ2, respectively. These unphysical model biases suggest tuning of the modeled radiation budgets. Two dynamically-driven regimes, based on the atmospheric vertical motion at 500 hPa (Ï500), are identified to provide a more quantitative measure of error in the radiation fields determined separately by biases in CF and CWP. These error types include the regime-averaged biases, biases in the sensitivity of TOA CREs to CF/CWP, and their co-variations. Overall, the biases in simulated CF and CWP are larger in the descent regime (Ï500 \u3e 25 hPa dayâ1) than in the ascent regime (Ï500 \u3c â25 hPa dayâ1), but are better correlated with observations. According to CERES observations, the sensitivity of LW CRE to CF is stronger in the ascent regime than in the decent regime (0.82 vs. 0.23 W mâ2 %â1) and the multimodel mean overestimates this value by ~40%. The difference in sensitivity of SW CRE to CF between the two regimes is less drastic (â1.34 vs. â1.12 W mâ2 %â1). TOA CREs rely independently on CWP in regions of large scale ascent and decent, as their sensitivities are similar between these two regimes (e.g., SW CRE/CWP = â0.28 W gâ1 for both regimes). In general, the total TOA CRE errors are heavily weighted by their biases in simulated sensitivity and biases in the simulated CF. A new observationally-constrained, data product is generated that can be used as a process-oriented diagnostic tool to further identify errors in simulated cloud and radiation fields. Based on the CloudSat and CALIPSO Ice Cloud Property Product (2C-ICE), and through one-dimensional radiative transfer modeling, a global database of radiative heating rate profiles is produced for non-precipitating single-layered ice clouds. Non-precipitating single-layered ice clouds have a global occurrence frequency of ~18% with considerable frequency in the tropical upper troposphere (13â16 km). A variety of ice cloud types exist in the sample of single-layered ice clouds developed here, which is determined by the distribution on cloud-top temperatures (CTT). For example, a peak in the distribution near 190 K (260 K) suggests the existence of cirrus (glaciated ice) clouds. The ice cloud microphysical properties responsible for having the largest impact on radiation (e.g., ice water content [IWC] and effective radius [Re]) are largest in the tropics and mid-latitudes according to 2C-ICE. Accordingly, this is where the strongest TOA SW absorption, and subsequently, the strongest upper tropospheric net radiative heating (\u3e 1.5 K dayâ1) occurs. This newly generated product will provide the data for which new ice cloud parameterizations can be developed in global models

The role of clouds in climate forcings and feedbacks: assessment using global modelling and satellite observations

Variability and change of the Earth\''s climate are of fundamental importance to humankind. In particular anthropogenic climate change has been considered widely as one of the most urgent concerns for the society (United Nations, 1992, 2002). It is therefore vital to improve the understanding of the Earth\''s climate system and its variability

Cloud Statistics from Calipso Lidar Data for the Performance Assessment of a Methane Space Lidar

In this thesis a performance assessment for the future German-French climate monitoring initiative, Methane Remote Sensing Lidar Mission (MERLIN), proposed by DLR and CNES in 2010 was undertaken. A general space lidar performance issue is the obstruction by optically dense clouds. For this purpose cloud free statistics, the global cloud top flatness and global cloud top distributions were derived from the Cloud-Aerosol Lidar and Infrared Path�nder Satellite Observation (CALIPSO) level 2, 333 m and 5 km lidar cloud-layer products between 01 January 2007 and 01 January 2008. Merging both data sets together thereby allowed the best possible simulation of near global and seasonal real world atmospheric conditions that a spaceborne Integrated Path Differential Absorption (IPDA) lidar like MERLIN will encounter. With 40.5 % overall global cloud free fraction, a cloud gap distribution which is following a power-law distribution with exponent 1.51 +-� 0.01 together with a mean cloud gap length of 7.41 km and about 200 daily global cloud top flatness events, the analysis reveals a dominance of small cloud gaps which is confirmed by a low median cloud gap length of only 1 km. While the cloud free fraction results were compared and confirmed with Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) seasonal and annual cloud fraction data, the power-law distribution of cloud gaps was confirmed by an extensive statistical analysis using maximum likelihood estimation, Kolmogorov-Smirnov statistics and likelihood ratio tests. Taking 6.05 x 10e8 individual CALIPSO measurements of the year 2007 with a horizontal resolution of 333 m and computing cloud gap and cloud free statistics for 2 �x 2� latitude/longitude grid points thereby identified regional and seasonal changes in the probability of spaceborne lidar surface detection. The analysis reveals that MERLIN will be able to perform near global methane mixing ratio column retrievals

Atmospheric Research 2013 Technical Highlights

Welcome to the Atmospheric Research 2013 Atmospheric Research Highlights report. This report, as before, is intended for a broad audience. Our readers include colleagues within NASA, scientists outside the Agency, science graduate students, and members of the general public. Inside are descriptions of atmospheric research science highlights and summaries of our education and outreach accomplishments for calendar year 2013.This report covers research activities from the Mesoscale Atmospheric Processes Laboratory, the Climate and Radiation Laboratory, the Atmospheric Chemistry and Dynamics Laboratory, and the Wallops Field Support Office under the Office of Deputy Director for Atmospheres (610AT), Earth Sciences Division in the Sciences and Exploration Directorate of NASAs Goddard Space Flight Center

Influence of Surface and Atmospheric Thermodynamic Properties on the Cloud Radiative Forcing and Radiative Energy Budget in the Arctic

The Arctic climate has changed significantly in the last decades, experiencing a dramatic loss of sea ice and stronger than global warming. The Arctic surface temperature and the growth or melt of sea ice is determined by the local surface energy budget. In this context, clouds are of essential importance as they strongly interact with the radiative fluxes and modulate the surface energy budget depending on their properties, the surface types, and atmospheric thermodynamics. For the quantification of changes in the radiative energy budget (REB) associated with the presence or absence of clouds, the concept of cloud radiative forcing (CRF) is commonly used. This concept is defined as the differences between the REB in cloudy and cloud-free conditions, two atmospheric states which can not be observed at the same location and time. Consequently, either radiative transfer simulations or observations in both states have to be related, both of which complicate the derivation of CRF. A review of available studies and their approaches to derive the CRF reveals conceptual differences as well as deficiencies in the handling of radiative processes related to the surface albedo. These findings call into question the current state of CRF assessment in the Arctic based on the few available studies, but also their comparability. By combining atmospheric radiative transfer simulations with a snow albedo model, two processes that control the surface albedo during the transition from cloud-free to cloudy conditions and their role in the derivation of CRF are discussed. The broadband surface albedo of snow surfaces typically increases in the presence of clouds due to a spectral weighting of downward irradiance toward shorter wavelengths. For more absorbing surface types such as white ice and melt ponds, which are common in summer, there is a strong shift between the albedo of direct and diffuse illuminated surface, which diminishes the surface albedo depending on the cloud optical thickness and solar zenith angle. In this thesis, a hypothesis on the impact of those surface-albedo--cloud interactions on the annual cycle of shortwave CRF is discussed, but an application to inner Arctic conditions remains an open issue. An improved method to derive the shortwave CRF is proposed and an application to two airborne campaigns in the marginal sea ice zone northwest of Svalbard (Norway) illustrates the role of surface-albedo--cloud interactions in the Arctic in spring and early summer. For the longwave CRF, conceptual differences and the general interpretation of the different CRF estimates are discussed and illustrated for a case study. Radiative transfer simulations of a rarely observed annual cycle of thermodynamic profiles in the inner Arctic are used to study both longwave CRF approaches and the impact of thermodynamic profiles on the longwave CRF. Making use of airborne low-level flights in the MIZ and other available datasets, common seasonal radiative states on sea ice and case studies of warm air intrusions and cold air outbreaks are illustrated. The CRF is analyzed as a function of the observed cloud/surface regime, which is extended by radiative transfer simulations characterizing the conditions in this region and seasons

Atmospheric Research 2011 Technical Highlights

The 2011 Technical Highlights describes the efforts of all members of Atmospheric Research. Their dedication to advancing Earth Science through conducting research, developing and running models, designing instruments, managing projects, running field campaigns, and numerous other activities, is highlighted in this report