Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

Liu, Y.; Wu, Wei; Jensen, Michael P.; Toto, Tami

doi:10.5194/acp-11-7155-2011

Cited by 53 publications

(58 citation statements)

References 68 publications

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“…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). Satellite retrievals of the CDR and EV have been used to extend the detailed knowledge gained from specific cloud campaign studies to the larger spatial and temporal scales that are relevant to climate (Liu et al, 2002(Liu et al, , 2011Bréon, 2006).…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

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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“…Numerous projects have been far studying different types of clouds [10][11][12][13] according to their origin and chemical constitution for global characteriza-tion of their basic properties such as optical thickness. However, although the debate on the accurate assessment of the atmospheric radiative budget is maintained by adequate consideration of clouds and aerosols in radiative models, it remains a fact that the lack of trustworthy input data contributes to maintain the already considerable differences about flux values obtained from different models [14]. Therefore, credible estimation of atmospheric radiative budget and hence the heating rate profile need local or regional data on cloud and aerosol microphysical and optical properties.…”

Section: Introductionmentioning

confidence: 99%

Shortwave Cloud and Aerosol Radiative Forcings and Their Effects on the Vertical Local Heating/Cooling Rates

Nguimdo¹,

Njomo²

2013

ACS

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An analysis of atmospheric SW-radiative forcing and local heating/cooling rate is made using a one year temporal and vertical profiles of aerosol and cloud over Yaoundé (11.51˚E, 3.83˚N). It appears that the direct influence of aerosols on the surface compared to the TOA can be 3 times larger. Annual mean value obtained at 559 mb altitude is +27.74 W/m 2 with range from 0 to +43 W/m 2 . At 904 mb, we obtained an annual mean of −46.22 W/m 2 with range from −65 to −9 W/m 2 . Frequency distribution indicates that more than 95% of ARF are between +10 and +70 W/m 2 at 559 mb (upper limit of UL), and more than 85% of ARF are between −70 and −10 W/m 2 at 904 mb (upper limit of PBL). This sign change is explained by the fact that the backscattering peaks at the upper limit of the aerosol PBL layer. The maximum CRF is noted at TOA where it reaches −600 W/m 2 based on the time interval and the structure of clouds. The highest values occur between 11.50 and 13.50 LST. Clouds lead to a general heating of the entire atmospheric column with a much greater effect near the surface. Aerosols effect on the heating rate profile show strong cooling during the day for the lower atmosphere, with slight heating at the upper atmosphere. This cooling contribution generally increases from the surface and peacks at the upper boundary of aerosol layer where reflectivity is the most important. Depending on the moment of the day, average heating effect of clouds peacks at surface or within the middle troposphere due to the absorption by clouds particles. Vertical profiles deeply evolve exhibiting differences that exceed −3 K/day according to altitude from one hour to another during a given mean solar day.

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“…Clouds play a dominant role within the Earth's radiation budget [1][2][3][4]. The warming effect induced by the increase of greenhouse gases might be modified by changes in the Earth's albedo on a regional or global scale.…”

Section: Introductionmentioning

confidence: 99%

“…For the Earth's albedo clouds play a quite important role, and the cloud albedo is frequently discussed within the scope of the planetary albedo and the cloud radiative forcing (e.g., [3]), as a consequence. However, the cloud albedo is a somehow theoretical quantity.…”

Section: Introductionmentioning

confidence: 99%

“…It is also not offered by the ESA Climate Change Initiative. Instead, large efforts went into the monitoring and analysis of specific cloud properties (e.g., [3,7,8] and references therein), where the cloud fraction, cloud optical depth (cloud liquid water path) and cloud top height have been essential variables of interest. However, data sets of cloud fraction, cloud optical depth and cloud top height which are derived from different satellites and with different retrieval methods reveal a wide dispersion of the respective variables (http://climserv.ipsl.polytechnique.fr/gewexca/) [9] This indicates that the generation of consistent data sets is still a challenge in science that can not easily be met.…”

Section: Introductionmentioning

confidence: 99%

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The Role of the Effective Cloud Albedo for Climate Monitoring and Analysis

et al. 2011

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Cloud properties and the Earth's radiation budget are defined as essential climate variables by the Global Climate Observing System (GCOS). The cloud albedo is a measure for the portion of solar radiation reflected back to space by clouds. This information is essential for the analysis and interpretation of the Earth's radiation budget and the solar surface irradiance. We present and discuss a method for the production of the effective cloud albedo and the solar surface irradiance based on the visible channel (0.45-1 µm) on-board of the Meteosat satellites. This method includes a newly developed self-calibration approach and has been used to generate a 23-year long continuous and validated climate data record of the effective cloud albedo and the solar surface irradiance. Using this climate data record we demonstrate the ability of the method to generate the two essential climate variables in high accuracy and homogeneity. Further on, we discuss the role of the cloud albedo within climate monitoring and analysis. We found trends with opposite sign in the observed effective cloud albedo resulting in positive trends in the solar surface irradiance over ocean and partly negative trends over land. Ground measurements are scarce over the ocean and thus satellite-derived effective cloud albedo and solar surface irradiance constitutes a unique observational data source. Within this scope it has to be considered that the ocean is the main energy reservoir of the Earth, which emphasises the role of Remote Sens. 2011, 3 2306 satellite-observed effective cloud albedo and derived solar surface irradiance as essential climate variables for climate monitoring and analysis.

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Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

Cited by 53 publications

References 68 publications

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

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

Shortwave Cloud and Aerosol Radiative Forcings and Their Effects on the Vertical Local Heating/Cooling Rates

The Role of the Effective Cloud Albedo for Climate Monitoring and Analysis

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