Abstract
The small-scale variability of fog over Paris-CdG airport was explored by using the twelve visibility measurements installed on runways. The variability inside this sub-kilometre area is significant for fog, whatever the studied fog characteristics. These results confirm that about 50% of fog is thin and heterogeneous at the airport scale. This study indicated that one point of measurement may be far from the representativeness of sub-kilometre scale area and can create problems when used for verifying numerical models. The fog characteristics cannot be captured by a local measurement of visibility, and it is not possible to deduce fog extension at the local scale from a local measurement, even for low visibility such as for LVP cases (Low Visibility Procedures). This work demonstrated with a perfect forecast framework that a large dispersion of forecast scores could be obtained when using one observation at the local-scale due to representativeness errors of visibility measurements. This dispersion has the same order of magnitude as the current NWP forecast quality of fog. An attempt to quantify the scale heterogeneity of fog was made using the Gini index. This index has allowed highlighting the appearance of waves during the dissipation phase of fog.
Highlights
Fog is a high-impact weather phenomenon affecting human activity and more air transportation
The criterion used to select fog events, i.e., at least one measurement unit of ParisCdG is under the low visibility threshold-LVT-(600 m), has detected a large amount of contiguous low visibility events; only 23% last for more than 10 min, 8.7% more than 30 min and 5% for more than an hour
The twelve visibility measurements installed at Paris-CdG allowed the estimation of spatial variability of visibility at sub-kilometre horizontal scale
Summary
Fog is a high-impact weather phenomenon affecting human activity and more air transportation. A reduction in visibility close to the ground is the most prominent feature of fog. Airport operations rely critically on sufficient visibility on the runways to maximize capacity in the air space. The disruption of airport transportation is extensive and very costly. Delays and landing diversions to other airports are caused by foggy conditions at airports. This implies substantial costs to companies and airports, comparable to the cost related to damage by tornadoes ([1]). In terms of passenger transportation, Paris Charles de Gaulle airport (Paris-CdG) is the biggest in France and the second biggest in Europe. At Paris-CdG, takeoffs and landings are reduced by a factor of two when visibility is below 600 m LVP condition (Low Visibility Procedures, for details see [3])
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