Statistical retrieval of thin liquid cloud microphysical properties using ground‐based infrared and microwave observations

Marke, Tobias; Ebell, Kerstin; Löhnert, Ulrich; Turner, David D.

doi:10.1002/2016jd025667

Cited by 22 publications

(22 citation statements)

References 41 publications

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“…The uncertainty of the LWP product is ±20 g/m 2 according to the manufacturer, but for relatively small LWP (<40 g/m 2 ) investigations indicate that the uncertainty is only ±5–10 g/m 2 , at least when the fog forms in clear sky so that a possible time‐independent bias can be corrected for (Marke et al . ; Wærsted et al . ).…”

Section: Observations Of Fog At the Sirta Observatorymentioning

confidence: 99%

Understanding the dissipation of continental fog by analysing the LWP budget using idealized LES and in situ observations

Wærsted

Haeffelin

Steeneveld

et al. 2019

Quart J Royal Meteoro Soc

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Funding informationDirection Générale de l'Armement (France), Meteomodem and the Netherlands Organization for Scientific Research (contract 863.10.010 and project number SH-312-15), Physical processes relevant for the dissipation of thick, continental fog after sunrise are studied through observations from the SIRTA observatory and idealized sensitivity studies with the large-eddy simulation model DALES. Observations of 250 fog events over 7 years show that more than half of the fog dissipations after sunrise are transitions to stratus lasting 2 hr or more. From the simulations, we quantify the contribution of each process to the liquid water path (LWP) budget of the fog. Radiative cooling is the main source of LWP, while surface turbulent heat fluxes are the most important process contributing to loss of LWP, followed by the absorption of solar radiation, the mixing with unsaturated air at the fog top and the deposition of cloud droplets. The loss of LWP by surface heat fluxes is very sensitive to the Bowen ratio, which is importantly affected by the availability of liquid water on the surface; in a run without liquid on the surface, fog dissipation occurred 85 min earlier than in the Baseline simulation. The variability of stratification and humidity above fog top is documented by 47 radiosondes and cloud radar. Using DALES, we find that the variability in stratification has an important impact on the entrainment velocity; a three times more rapid fog-top entrainment enables the cloud base to lift from the ground 90 min earlier in weak stratification than in strong stratification in the model. With relatively dry overlying air, the fog evaporates faster than if the air is near saturation, leading to 70 min earlier dissipation in our simulations. Continuous observations of the temperature and humidity profiles of the layer overlying the fog could therefore be useful for understanding and anticipating fog dissipation.

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Section: Observations Of Fog At the Sirta Observatorymentioning

confidence: 99%

Understanding the dissipation of continental fog by analysing the LWP budget using idealized LES and in situ observations

Wærsted

Haeffelin

Steeneveld

et al. 2019

Quart J Royal Meteoro Soc

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“…The two-way uncertainty of the gas attenuation estimated by Hogan and O'Connor (2004) is about 10 %. The uncertainty of 25 g m −2 in LWP from MWR causes about ±0.2 dB uncertainty in the two-way attenuation at the W-band (Matrosov, 2009).…”

Section: Ghz Radarmentioning

confidence: 99%

Statistics on clouds and their relation to thermodynamic conditions at Ny-Ålesund using ground-based sensor synergy

et al. 2019

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Abstract. The French–German Arctic research base AWIPEV (the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research – AWI – and the French Polar Institute Paul Emile Victor – PEV) at Ny-Ålesund, Svalbard, is a unique station for monitoring cloud-related processes in the Arctic. For the first time, data from a set of ground-based instruments at the AWIPEV observatory are analyzed to characterize the vertical structure of clouds. For this study, a 14-month dataset from Cloudnet combining observations from a ceilometer, a 94 GHz cloud radar, and a microwave radiometer is used. A total cloud occurrence of ∼81 %, with 44.8 % multilayer and 36 % single-layer clouds, was found. Among single-layer clouds the occurrence of liquid, ice, and mixed-phase clouds was 6.4 %, 9 %, and 20.6 %, respectively. It was found that more than 90 % of single-layer liquid and mixed-phase clouds have liquid water path (LWP) values lower than 100 and 200 g m−2, respectively. Mean values of ice water path (IWP) for ice and mixed-phase clouds were found to be 273 and 164 g m−2, respectively. The different types of single-layer clouds are also related to in-cloud temperature and the relative humidity under which they occur. Statistics based on observations are compared to ICOsahedral Non-hydrostatic (ICON) model output. Distinct differences in liquid-phase occurrence in observations and the model at different environmental temperatures lead to higher occurrence of pure ice clouds. A lower occurrence of mixed-phase clouds in the model at temperatures between −20 and −5 ∘C becomes evident. The analyzed dataset is useful for satellite validation and model evaluation.

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“…The integrated water vapour (IWV) is more reliable with an uncertainty of ±0.2 kg m −2 , while the estimate of LWP in general has an uncertainty of ±20 g m −2 , according to the manufacturer. However, for small LWP (< 50 g m −2 ), investigations by Marke et al (2016) indicate that the absolute uncertainties are smaller, with a root mean square (rms) error of 6.5 g m −2 . Moreover, much of the uncertainty in retrieving LWP is due to uncertainties in atmospheric conditions, such as cloud temperature and humidity profile (e.g.…”

Section: Observational Site and Instrumentationmentioning

confidence: 99%

Radiation in fog: quantification of the impact on fog liquid water based on ground-based remote sensing

Wærsted¹,

Haeffelin

Dupont

et al. 2017

Atmos. Chem. Phys.

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Abstract. Radiative cooling and heating impact the liquid water balance of fog and therefore play an important role in determining their persistence or dissipation. We demonstrate that a quantitative analysis of the radiation-driven condensation and evaporation is possible in real time using groundbased remote sensing observations (cloud radar, ceilometer, microwave radiometer). Seven continental fog events in midlatitude winter are studied, and the radiative processes are further explored through sensitivity studies. The longwave (LW) radiative cooling of the fog is able to produce 40-70 g m −2 h −1 of liquid water by condensation when the fog liquid water path exceeds 30 g m −2 and there are no clouds above the fog, which corresponds to renewing the fog water in 0.5-2 h. The variability is related to fog temperature and atmospheric humidity, with warmer fog below a drier atmosphere producing more liquid water. The appearance of a cloud layer above the fog strongly reduces the LW cooling relative to a situation with no cloud above; the effect is strongest for a low cloud, when the reduction can reach 100 %. Consequently, the appearance of clouds above will perturb the liquid water balance in the fog and may therefore induce fog dissipation. Shortwave (SW) radiative heating by absorption by fog droplets is smaller than the LW cooling, but it can contribute significantly, inducing 10-15 g m −2 h −1 of evaporation in thick fog at (winter) midday. The absorption of SW radiation by unactivated aerosols inside the fog is likely less than 30 % of the SW absorption by the water droplets, in most cases. However, the aerosols may contribute more significantly if the air mass contains a high concentration of absorbing aerosols. The absorbed radiation at the surface can reach 40-120 W m −2 during the daytime depending on the fog thickness. As in situ measurements indicate that 20-40 % of this energy is transferred to the fog as sensible heat, this surface absorption can contribute significantly to heating and evaporation of the fog, up to 30 g m −2 h −1 for thin fog, even without correcting for the typical underestimation of turbulent heat fluxes by the eddy covariance method. Since the radiative processes depend mainly on the profiles of temperature, humidity and clouds, the results of this paper are not site specific and can be generalised to fog under different dynamic conditions and formation mechanisms, and the methodology should be applicable to warmer and moister climates as well. The retrieval of approximate emissivity of clouds above fog from cloud radar should be further developed.

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Statistical retrieval of thin liquid cloud microphysical properties using ground‐based infrared and microwave observations

Cited by 22 publications

References 41 publications

Understanding the dissipation of continental fog by analysing the LWP budget using idealized LES and in situ observations

Understanding the dissipation of continental fog by analysing the LWP budget using idealized LES and in situ observations

Statistics on clouds and their relation to thermodynamic conditions at Ny-Ålesund using ground-based sensor synergy

Radiation in fog: quantification of the impact on fog liquid water based on ground-based remote sensing

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