Bingqi Yi

On the Radiative Properties of Ice Clouds: Light Scattering, Remote Sensing, and Radiation Parameterization

Presented is a review of the radiative properties of ice clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the single-scattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed. With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared (IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed. The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models (GCMs). The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate studies is proven.

Impact of radiatively interactive dust aerosols in the NASA GEOS-5 climate model: Sensitivity to dust particle shape and refractive index

The radiative effects of Saharan dust aerosols are investigated in the NASA GEOS-5 atmospheric general circulation model. A sectional aerosol microphysics model (CARMA) is run online in GEOS-5. CARMA treats the dust aerosol lifecycle, and its tracers are radiatively coupled to GEOS-5. A series of AMIP-style simulations are performed, in which input dust optical properties (particle shape and refractive index) are varied. Simulated dust distributions for summertime Saharan dust compare well to observations, with best results found when the most absorbing dust optical properties are assumed. Dust absorption leads to a strengthening of the summertime Hadley cell circulation, increased dust lofting to higher altitudes, and a strengthening of the African easterly jet, resulting in increased dust atmospheric lifetime and farther northward and westward transport. We find a positive feedback of dust radiative forcing on emissions, in contrast with previous studies, which we attribute to our having a relatively strong longwave forcing caused by our simulating larger effective particle sizes. This longwave forcing reduces the magnitude of midday net surface cooling relative to other studies, and leads to a nighttime warming that results in higher nighttime wind speeds and dust emissions. The radiative effects of dust particle shape have only minor impact on transport and emissions, with small (~5%) impact on top of atmosphere shortwave forcing, in line with previous studies, but relatively more pronounced effects on shortwave atmospheric heating and surface forcing (~20% increase in atmospheric forcing for spheroids). Shape effects on longwave heating terms are of order ~10%.

Influence of Ice Particle Surface Roughening on the Global Cloud Radiative Effect

AbstractIce clouds influence the climate system by changing the radiation budget and large-scale circulation. Therefore, climate models need to have an accurate representation of ice clouds and their radiative effects. In this paper, new broadband parameterizations for ice cloud bulk scattering properties are developed for severely roughened ice particles. The parameterizations are based on a general habit mixture that includes nine habits (droxtals, hollow/solid columns, plates, solid/hollow bullet rosettes, aggregate of solid columns, and small/large aggregates of plates). The scattering properties for these individual habits incorporate recent advances in light-scattering computations. The influence of ice particle surface roughness on the ice cloud radiative effect is determined through simulations with the Fu–Liou and the GCM version of the Rapid Radiative Transfer Model (RRTMG) codes and the National Center for Atmospheric Research Community Atmosphere Model (CAM, version 5.1). The differences in sh...

Impact of aviation on climate: FAA’s Aviation Climate Change Research Initiative (ACCRI) Phase II

AbstractUnder the Federal Aviation Administration’s (FAA) Aviation Climate Change Research Initiative (ACCRI), non-CO2 climatic impacts of commercial aviation are assessed for current (2006) and for future (2050) baseline and mitigation scenarios. The effects of the non-CO2 aircraft emissions are examined using a number of advanced climate and atmospheric chemistry transport models. Radiative forcing (RF) estimates for individual forcing effects are provided as a range for comparison against those published in the literature. Preliminary results for selected RF components for 2050 scenarios indicate that a 2% increase in fuel efficiency and a decrease in NOx emissions due to advanced aircraft technologies and operational procedures, as well as the introduction of renewable alternative fuels, will significantly decrease future aviation climate impacts. In particular, the use of renewable fuels will further decrease RF associated with sulfate aerosol and black carbon. While this focused ACCRI program effort...

Estimation of Errors in Two-Stream Approximations of the Solar Radiative Transfer Equation for Cloudy-Sky Conditions

AbstractSolar flux densities and heating rates predicted by a broadband, multilayer δ-Eddington two-stream approximation are compared to estimates from a Monte Carlo model that uses detailed descriptions of cloud particle phase functions and facilitates locally nonzero net horizontal flux densities. Results are presented as domain averages for 256-km sections of cloudy atmospheres inferred from A-Train satellite data: 32 632 samples for January 2007 between 70°S and 70°N with total cloud fraction C > 0.05. The domains are meant to represent grid cells of a conventional global climate model and consist of columns of infinite width across track and Δx ≈ 1 km along track. The δ-Eddington was applied in independent column approximation (ICA) mode, while the Monte Carlo was applied using both Δx → ∞ (i.e., ICA) and Δx ≈ 1 km. Mean-bias errors due to the δ-Eddington’s neglect of phase function details and horizontal transfer, as functions of cosine of solar zenith angle μ0, are comparable in magnitude and have ...

Aerosol-cloud-precipitation relationships from satellite observations and global climate model simulations

Substantial uncertainties exist in the current knowledge of aerosol-cloud-precipitation relationships and stem from the complicated interactions among the atmospheric constituents. We use a straightforward statistical method, the regression analysis technique, to examine the aerosol-cloud-precipitation relationships from satellite observational data sets, including the aqua moderate resolution imaging spectroradiometer (MODIS) aerosol and cloud products and the tropical rainfall measuring mission (TRMM) precipitation rate. Furthermore, the conventional MODIS aerosol product is combined with the Deep Blue algorithm product to reconstruct a complete global map of aerosol optical depth. Numerical simulations using the latest version of the community earth system model (CESM) are also carried out. Globally, distinct statistically significant relationships between aerosol optical depth, cloud fraction, and precipitation rate are obtained over both land and ocean. Signals agreeing with the first and second indirect effects of aerosols are detected, but other factors are likely contributors. The modeling results are found to generally agree with satellite observations, but the model usually overestimates the aerosol-cloud-precipitation relationship. An increasing trend in cloud fraction with the increase of aerosol optical depth (AOD) over ocean regions is found in the observations, while the reverse is true in the model simulation. It is mostly consistent that the model and observation both show a negative relationship between AOD and precipitation rate over land and a positive relationship over ocean.

Impact of pollution on the optical properties of trans‐Pacific East Asian dust from satellite and ground‐based measurements

We investigate changes in the optical properties of a large dust plume originating from East Asian deserts during its transport over the northwestern Pacific Ocean in March 2013. The study makes use of observational products from two sensors in the NASA A-Train satellite constellation, the Moderate Resolution Imaging Spectroradiometer and the Cloud-Aerosol Lidar with Orthogonal Polarization. Forward trajectory clustering analysis and satellite observations show that dust initiating from the Taklimakan and Gobi deserts experienced thorough mixing with industrial pollution aerosols shortly after leaving the source region and were lofted by a strong midlatitude weather system to more than 4 km in height. The dust plume accompanied the weather system and reached the east coast of the North American continent within 7–10 days. The dust aerosols became spectrally absorptive during transport due to mixing with other aerosol types such as soot. Furthermore, a decrease in the depolarization ratio suggests that the complexities in aerosol particle morphologies were reduced during transport over the ocean. More than half of the dust aerosol layers surviving the trans-Pacific transport were polluted and exhibited different optical properties and radiative effects from those of pure dust.

Effect of black carbon on dust property retrievals from satellite observations

Abstract The effect of black carbon on the optical properties of polluted mineral dust is studied from a satellite remote-sensing perspective. By including the auxiliary data of surface reflectivity and aerosol mixing weight, the optical properties of mineral dust, or more specifically, the aerosol optical depth (AOD) and single-scattering albedo (SSA), can be retrieved with improved accuracy. Precomputed look-up tables based on the principle of the Deep Blue algorithm are utilized in the retrieval. The mean differences between the retrieved results and the corresponding ground-based measurements are smaller than 1% for both AOD and SSA in the case of pure dust. However, the retrievals can be underestimated by as much as 11.9% for AOD and overestimated by up to 4.1% for SSA in the case of polluted dust with an estimated 10% (in terms of the number-density mixing ratio) of soot aggregates if the black carbon effect on dust aerosols is neglected.

Response of Aerosol Direct Radiative Effect to the East Asian Summer Monsoon

Asian summer monsoon and atmospheric aerosol simultaneously influence the climate in the East Asian region. However, substantial uncertainties exist in the current understanding of the interactions between monsoon and aerosol and their combined effects. Previous studies have shown that aerosols influence the strength of monsoon and monsoon-related water cycles; however, monsoon strongly regulates the aerosol spatial distribution. This letter investigates the radiative flux response at the top of the atmosphere to the Asian summer monsoon by using observations made by the Clouds and Earths Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer. In comparison with the ten-year (2002-2011) mean climatology, the aerosol radiative effect is estimated over two eastern Asia regions for the months of July in 2002 and 2003, corresponding to a weak and a strong summer monsoon event, respectively. The dramatically different influences show the aerosol radiative forcing over land to be strongly responsive to Asian summer monsoon. Furthermore, the reanalysis-based estimate of the aerosol radiative effect is consistent with its observation-only counterpart.

Optical properties of ice clouds: new modeling capabilities and relevant applications

A combination of the invariant imbedding T-matrix (II-TM) method, the improved geometric-optics method (IGOM), and the pseudo-spectral time domain (PSTD) method provides advanced modeling capabilities to simulate the singlescattering properties of ice crystals for the entire size parameter range. The downstream applications of the singlescattering properties simulated from the new modeling capabilities, and, consequently, the bulk radiative properties render significant improvements, particularly, in remote sensing implementations involving ice clouds. Furthermore, the single-scattering properties of individual ice crystals are simulated. In addition, a sensitivity study is performed regarding the application of the single-scattering properties to remote sensing of ice cloud properties based on spaceborne observations.