Global distribution of cloud droplet effective radius from POLDER polarization measurements

Bréon, François‐Marie; Colzy, Stéphane

doi:10.1029/2000gl011691

Cited by 41 publications

(35 citation statements)

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“…Note that this retains the difference between land and ocean values, differently from Kiehl and Shields (2013), who used a single effective cloud droplet radius globally. There is little knowledge about the actual aerosol concentration during the Eocene, but present-day observations in remote regions indicate that a land-sea differ-ence in droplet size can be expected even in the absence of anthropogenic emissions (Bréon and Colzy, 2000).…”

Section: Model and Simulationsmentioning

confidence: 99%

Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene

Carlson

Caballero

2017

Clim. Past

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Abstract. Recent work in modelling the warm climates of the early Eocene shows that it is possible to obtain a reasonable global match between model surface temperature and proxy reconstructions, but only by using extremely high atmospheric CO 2 concentrations or more modest CO 2 levels complemented by a reduction in global cloud albedo. Understanding the mix of radiative forcing that gave rise to Eocene warmth has important implications for constraining Earth's climate sensitivity, but progress in this direction is hampered by the lack of direct proxy constraints on cloud properties. Here, we explore the potential for distinguishing among different radiative forcing scenarios via their impact on regional climate changes. We do this by comparing climate model simulations of two end-member scenarios: one in which the climate is warmed entirely by CO 2 (which we refer to as the greenhouse gas (GHG) scenario) and another in which it is warmed entirely by reduced cloud albedo (which we refer to as the "low CO 2 -thin clouds" or LCTC scenario) . The two simulations have an almost identical global-mean surface temperature and equator-to-pole temperature difference, but the LCTC scenario has ∼ 11 % greater global-mean precipitation than the GHG scenario. The LCTC scenario also has cooler midlatitude continents and warmer oceans than the GHG scenario and a tropical climate which is significantly more El Niño-like. Extremely high warm-season temperatures in the subtropics are mitigated in the LCTC scenario, while cool-season temperatures are lower at all latitudes. These changes appear large enough to motivate further, more detailed study using other climate models and a more realistic set of modelling assumptions.

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Section: Model and Simulationsmentioning

confidence: 99%

Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene

Carlson

Caballero

2017

Clim. Past

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“…The presence of organic acids, in addition to inorganic species such as sulfate and potassium chloride, provides more than enough solubility for smoke particles to activate cloud droplets. Consequently, observations of significant decreases in cloud droplet size and of increased reflectivity due to smoke particle activation are commonly reported (e.g., Hudson et al, 1991;Kaufman and Fraser, 1997;Reid et al, 1999b;Breon and Colzy, 2000), and precipitation effects are currently under study (Rosenfeld, 1999).…”

Section: Particle Thermodynamicsmentioning

confidence: 99%

A review of biomass burning emissions part II: intensive physical properties of biomass burning particles

Reid¹,

et al. 2005

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Abstract. The last decade has seen tremendous advances in atmospheric aerosol particle research that is often performed in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, has been closely studied for its radiative, geochemical, and dynamic impacts. These studies have taken many forms including laboratory burns, in situ experiments, remote sensing, and modeling. While the differing perspectives of these studies have ultimately improved our qualitative understanding of biomass-burning issues, the varied nature of the work make inter-comparisons and resolutions of some specific issues difficult. In short, the literature base has become a milieu of small pieces of the biomass-burning puzzle. This manuscript, the second part of four, examines the properties of biomass-burning particle emissions. Here we review and discuss the literature concerning the measurement of smoke particle size, chemistry, thermodynamic properties, and emission factors. Where appropriate, critiques of measurement techniques are presented. We show that very large differences in measured particle properties have appeared in the literature, in particular with regards to particle carbon budgets. We investigate emissions uncertainties using scale analyses, which shows that while emission factors for grass and brush are relatively well known, very large uncertainties still exist in emission factors of boreal, temperate and some tropical forests. Based on an uncertainty analysis of the community data set of biomass burning measurements, we present simplified models for particle size and emission factors. We close this review paper with a discussion of the community experimental data, point to lapses in the data set, and prioritize future research topics.

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“…One of the key radiative properties of liquid water clouds is the droplet size distribution, which is represented by the droplet effective radius (CDR) and the effective variance (EV) (Bréon and Doutriaux-Boucher, 2005;Bréon and Colzy, 2000;Hansen and Travis, 1974). The observation of CDR and EV not only has a significant influence on the modeling of clouds' climate feedbacks (Stubenrauch et al, 2013;Dandin et al, 1997) but is also meaningful to aerosol-cloud-precipitation interaction research (Penner et al, 2004;Shang et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…The measurements for the various pixels are acquired with different viewing geometries so that the combination of the observations provides near-continuous directional sampling of the polarization signature. However, this method relies on the assumption of homogeneity in the cloud over large distances (Bréon and Doutriaux-Boucher, 2005;Bréon and Colzy, 2000). Actual clouds may not satisfy the homogeneity assumption (Schutgens and Roebeling, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…In the scattering angle range of 135 to 165 • (the rainbow region), the polarized reflectance in the non-absorbing visible and infrared bands exhibits several peaks and troughs, i.e., supernumerary cloudbow. The angular positions of these peaks are exclusively sensitive to CDR; moreover, the polarization amplitudes are sensitive to the EV (Bréon and Colzy, 2000). The polarized reflectance is proportional to the polarized phase function (the phase matrix elements P 12 computed using Lorenz-Mie theory).…”

Section: Introductionmentioning

confidence: 99%

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Impact of cloud horizontal inhomogeneity and directional sampling on the retrieval of cloud droplet size by the POLDER instrument

et al. 2015

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Abstract. The principles of cloud droplet size retrieval via Polarization and Directionality of the Earth's Reflectance (POLDER) requires that clouds be horizontally homogeneous. The retrieval is performed by combining all measurements from an area of 150 km × 150 km to compensate for POLDER's insufficient directional sampling. Using POLDER-like data simulated with the RT3 model, we investigate the impact of cloud horizontal inhomogeneity and directional sampling on the retrieval and analyze which spatial resolution is potentially accessible from the measurements. Case studies show that the sub-grid-scale variability in droplet effective radius (CDR) can significantly reduce valid retrievals and introduce small biases to the CDR (∼ 1.5 µm) and effective variance (EV) estimates. Nevertheless, the sub-grid-scale variations in EV and cloud optical thickness (COT) only influence the EV retrievals and not the CDR estimate. In the directional sampling cases studied, the retrieval using limited observations is accurate and is largely free of random noise.Several improvements have been made to the original POLDER droplet size retrieval. For example, measurements in the primary rainbow region (137-145 • ) are used to ensure retrievals of large droplet (> 15 µm) and to reduce the uncertainties caused by cloud heterogeneity. We apply the improved method using the POLDER global L1B data from June 2008, and the new CDR results are compared with the operational CDRs. The comparison shows that the operational CDRs tend to be underestimated for large droplets because the cloudbow oscillations in the scattering angle region of 145-165 • are weak for cloud fields with CDR > 15 µm. Finally, a sub-grid-scale retrieval case demonstrates that a higher resolution, e.g., 42 km × 42 km, can be used when inverting cloud droplet size distribution parameters from POLDER measurements.

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Global distribution of cloud droplet effective radius from POLDER polarization measurements

Cited by 41 publications

References 8 publications

Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene

Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene

A review of biomass burning emissions part II: intensive physical properties of biomass burning particles

Impact of cloud horizontal inhomogeneity and directional sampling on the retrieval of cloud droplet size by the POLDER instrument

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