Radiation fog formation alerts using attenuated backscatter power from automatic lidars and ceilometers
Radiation fog occurs over many locations around the world in stable atmospheric conditions. Air traffic at busy airports can be significantly disrupted because low visibility at the ground makes it unsafe to take off, land and taxi on the ground. Current numerical weather prediction forecasts ar...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/9/5347/2016/amt-9-5347-2016.pdf |
| Summary: | Radiation fog occurs over many locations around the world in stable
atmospheric conditions. Air traffic at busy airports can be significantly
disrupted because low visibility at the ground makes it unsafe to take off,
land and taxi on the ground. Current numerical weather prediction forecasts
are able to predict general conditions favorable for fog formation, but not
the exact time or location of fog occurrence. A selected set of observations
available in near-real time at strategic locations could also be useful to
track the evolution of key processes and key parameters that drive fog
formation. Such observations could complement the information predicted by
numerical weather prediction (NWP) models that is made available to airport forecasters in support of their
fog forecast. This paper presents an experimental setup based on collocated
automatic lidar and ceilometer measurements, relative humidity measurements
and horizontal visibility measurements to study hygroscopic growth of fog
condensation nuclei. This process can take several minutes to hours, and can
be tracked using lidar- or ceilometer-attenuated backscatter profiles. Based
on hygroscopic growth laws we derive a set of parameters that can be used to
provide alerts minutes to hours prior to formation of radiation fog. We
present an algorithm that uses the temporal evolution of attenuated
backscatter measurements to derive pre-fog formation alerts. The performance
of the algorithm is tested on 45 independent pre-fog situations at two
locations (near Paris, France, and Brussels, Belgium). We find that an alert
for pre-fog conditions predominantly occurs 10–50 min prior to fog formation
at an altitude ranging 0 to 100 m above ground. In a few cases, alerts can
occur up to 100 min prior to fog formation. Alert durations are found to be
sensitive to the relative humidity conditions found a few hours prior to the
fog. |
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| ISSN: | 1867-1381 1867-8548 |