The clear‐sky index to separate clear‐sky from cloudy‐sky situations in climate research

Marty, Christoph; Philipona, Rolf

doi:10.1029/2000gl011743

Cited by 96 publications

(92 citation statements)

References 7 publications

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“…The attraction of this measure is that LDR is relatively insensi- tive to the solar position, and so should be independent of the other factors influencing J (O 1 D). An attempt at using LDR has been made using half-hourly long-wave radiation averaged values measured at Cape Grim (Wilson and Shinkfield, 2007) to derive the clear-sky index (Marty and Philipona, 2000). In this case it was possible to produce a fit extending Eq.…”

Section: Cloud Impactmentioning

confidence: 99%

“…While sun photometers make measurements during this period, they do not make measurements of cloud optical depth as has been used elsewhere (Anton et al, 2012). Long-wave downward radiation (LDR) measurements have been used to estimate cloudiness (Marty and Philipona, 2000;Dürr and Philipona, 2004). The attraction of this measure is that LDR is relatively insensi- tive to the solar position, and so should be independent of the other factors influencing J (O 1 D).…”

Section: Cloud Impactmentioning

confidence: 99%

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Characterisation of J(O1D) at Cape Grim 2000–2005

Wilson

2015

Atmos. Chem. Phys.

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Abstract.Estimates of the rate of production of excited oxygen atoms due to the photolysis of ozone (J (O 1 D)) have been derived from radiation measurements carried out at Cape Grim, Tasmania (40.6 • S, 144.7 • E). The individual measurements have a total uncertainty of 16 % (1σ ). These estimates agree well with model estimates of clear-sky photolysis rates. Observations spanning 2000-2005 have been used to quantify the impact of season, clouds and ozone column amount. The annual cycle of J (O 1 D) has been investigated via monthly means. These means show an interannual variation (monthly standard deviation) of 9 %, but in midsummer and midwinter this reduces to 3-5 %. Variations in solar zenith angle and total column ozone explain 86 % of the observed variability in the measured photolysis rates. The impact of total column ozone, expressed as a radiation amplification factor (RAF), is found to be ∼ 1.53, in agreement with model estimates. This ozone dependence explains 20 % of the variation observed at medium solar zenith angles (30-50 • ). The impact of clouds results in a median reduction of 30 % in J (O 1 D) for the same solar zenith angle range. Including estimates of cloudiness derived from long-wave radiation measurements resulted in a statistically significant fit to observations, but the quality of the fit did not increase significantly as measured by the adjusted R 2 .

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Section: Cloud Impactmentioning

confidence: 99%

Section: Cloud Impactmentioning

confidence: 99%

Characterisation of J(O1D) at Cape Grim 2000–2005

Wilson

2015

Atmos. Chem. Phys.

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“…Long and Ackerman (2000) present a method to estimate cloud fraction (N ) using global and diffuse solar radiation measurements, which limits the application to daytime periods, and to locations where diffuse shortwave radiation is measured. Marty and Philipona (2000) present the Clear-Sky Index to separate clear and cloudy skies using longwave radiation measurements, the derivation of which is based, to a large extent, on Konzelmann et al (1994). Dürr and Philipona (2004) extend the Clear-Sky Index to an algorithm that retrieves N from downwelling longwave measurements.…”

Section: Introductionmentioning

confidence: 99%

Assessing the retrieval of cloud properties from radiation measurements over snow and ice

Munneke

Reijmer

Broeke

2011

Intl Journal of Climatology

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ABSTRACT:We critically review and improve a simple method to extract year-round records of cloud optical thickness from radiation measurements made by automatic weather stations (AWSs) over snow and ice surfaces. A 'longwaveequivalent cloudiness', N ε , obtained from longwave radiation measurements, is combined with the effective cloud optical thickness, τ , from shortwave data, to obtain consistent, year-round information on cloud properties. The method is applied to radiation data from six AWSs in Dronning Maud Land, Antarctica, and the ablation area of the West-Greenland ice sheet. The good correlation between daily-mean N ε and τ for all locations (0.77 < r < 0.94) shows that shortwave radiative properties of clouds can be inferred using longwave radiation even in the absence of solar radiation itself. An error analysis shows that retrievals of τ are sensitive to the quality of the input data, but accurate to about 21% for hourly values, 11% for daily means, and about 6% for monthly means. As three applications of the method presented above, we discuss the influence of clouds on the radiation budget (Application I), the relation between cloud cover and broadband albedo (Application II) at the six AWS locations, and we demonstrate the possibility to detect trends in τ in longer data series (Application III). About one-third of the attenuation of solar radiation by clouds is compensated by multiple reflections between the high-albedo surface and the cloud base (Application I). Cloudy-sky surface albedo is higher than the clear-sky albedo for snow surfaces but not for ice (Application II): over snow surfaces, clouds deplete near-infrared (IR) radiation and thus increase the broadband albedo. Ice surfaces have a much lower albedo for visible radiation, weakening this enrichment of visible radiation and thus the increase of broadband albedo. The method is used to detect a trend in τ of −0.40 ± 0.15 y −1 in the 1995-2004 time series from Neumayer, Antarctica (Application III).

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“…In correlation experiments of the nighttime offsets with the longwave net flux, a rather low coefficient of determination of 0.31 was found and even multiple correlations, including additionally e.g., the air temperature, wind speed, case temperatures or the clear-sky index (Marty and Philipona, 2000), the latter related to cloud cover, could only increase r 2 towards 0.56. We attribute this rather poor performance to the stepwise signals of the nighttime offsets induced by our DAQ resolution as correlations found in most other studies are significantly higher.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, irradiance solar position (azimuth and zenith) and the clear-sky index (Marty and Philipona, 2000) are stored in this database table. The clear-sky index is used to separate clear-sky from cloudy days in further analysis.…”

Section: Automated Quality Controlmentioning

confidence: 99%

The Austrian radiation monitoring network ARAD – best practice and added value

et al. 2016

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Abstract. The Austrian RADiation monitoring network (ARAD) has been established to advance the national climate monitoring and to support satellite retrieval, atmospheric modeling and the development of solar energy techniques. Measurements cover the downward solar and thermal infrared radiation using instruments according to Baseline Surface Radiation Network (BSRN) standards. A unique feature of ARAD is its vertical dimension of five stations, covering an altitude range between about 200 m a.s.l (Vienna) and 3100 m a.s.l. (BSRN site Sonnblick). The paper outlines the aims and scopes of ARAD, its measurement and calibration standards, methods, strategies and station locations. ARAD network operation uses innovative data processing for quality assurance and quality control, utilizing manual and automated control algorithms. A combined uncertainty estimate for the broadband shortwave radiation fluxes at all five ARAD stations, using the methodology specified by the Guide to the Expression of Uncertainty in Measurement indicates that relative accuracies range from 1.5 to 2.9 % for large signals (global, direct: 1000 W m −2 , diffuse: 500 W m −2 ) and from 1.7 to 23 % (or 0.9 to 11.5 W m −2 ) for small signals (50 W m −2 ) (expanded uncertainties corresponding to the 95 % confidence level). If the directional response error of the pyranometers and the temperature response of the instruments and the data acquisition system (DAQ) are corrected, this expanded uncertainty reduces to 1.4 to 2.8 % for large signals and to 1.7 to 5.2 % (or 0.9-2.6 W m −2 ) for small signals. Thus, for large signals of global and diffuse radiation, BSRN target accuracies are met or nearly met (missed by less than 0.2 percentage points, pps) for 70 % of the ARAD measurements after this correction. For small signals of direct radiation, BSRN targets are achieved at two sites and nearly met (also missed by less than 0.2 pps) at the other sites. For small signals of global and diffuse radiation, targets are achieved at all stations. Additional accuracy gains can be achieved in the future through additional measurements, corrections and a further upgrade of the DAQ. However, to improve the accuracy of measurements of direct solar radiation, improved instrument accuracy is needed. ARAD could serve as a useful example for establishing state-of-the-art radiation monitoring at the national level with a multiple-purpose approach. Instrumentation, guidelines and tools (such as the data quality control) developed within ARAD are intended to increase monitoring capabilities of global radiation and thus designed to allow straightforward adoption in other regions, without high development costs.

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The clear‐sky index to separate clear‐sky from cloudy‐sky situations in climate research

Cited by 96 publications

References 7 publications

Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

Assessing the retrieval of cloud properties from radiation measurements over snow and ice

The Austrian radiation monitoring network ARAD – best practice and added value

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The clear‐sky index to separate clear‐sky from cloudy‐sky situations in climate research

Cited by 96 publications

References 7 publications

Characterisation of &lt;i&gt;J&lt;/i&gt;(O&lt;sup&gt;1&lt;/sup&gt;D) at Cape Grim 2000–2005

Characterisation of &lt;i&gt;J&lt;/i&gt;(O&lt;sup&gt;1&lt;/sup&gt;D) at Cape Grim 2000–2005

Assessing the retrieval of cloud properties from radiation measurements over snow and ice

The Austrian radiation monitoring network ARAD – best practice and added value

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Product

Resources

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Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005

Characterisation of <i>J</i>(O<sup>1</sup>D) at Cape Grim 2000–2005