PARAFOG: a new decision support system for the airports to monitor and to predict radiation fog based on automatic LIDARceilometer

Transcription

1 PARAFOG: a new decision support system for the airports to monitor and to predict radiation fog based on automatic LIDARceilometer measurements Quentin Laffineur Royal Meteorological Institute of Belgium

2 Outline Introduction PARAFOG: description PARAFOG: fog case analysis PARAFOG: its uses in practice Conclusions 2

3 Outline Introduction PARAFOG: description PARAFOG: fog case analysis PARAFOG: its uses in practice Conclusions 3

4 Introduction From 20 th to 24 th December 2006: Thick fog event at Heathrow. Up to 1,000 cancelled flights. Up to 800,000 people impacted. Human and financial cost. Aeronautical authorities wish to minimize it by having reliable fog forecast. 4

5 Introduction Most airports are equipped with ALCs (CBH measurements) ALC have nominal optical overlap at very low range gate, Useful to analyse the ALC signal (backscatter) in the boundary layer ALC principle - Backscatter signal (β ) is the amount of light sent into the sky by the ALC that is backscattered by cloud, aerosol... - β is measured in function of the altitude by the ALC. Useful to monitor first formation stage of fog (hydroscopic growth) Potentially contains major information to predict fog formation or not. 5

6 Outline Introduction PARAFOG: description PARAFOG: fog case analysis PARAFOG: its uses in practice Conclusions 6

7 PARAFOG PARAFOG: uses backscatter signal to derive pre-fog formation coupled with the standard surface observations. PARAFOG: developed in collaboration with SIRTA/RMI in the framework of TOPROF (COST Action ES1303) activities. PARAFOG: supports the fog forecast in near-real time as a complement to the information predicted by NWP models. 7

8 PARAFOG: physical principle Water vapor liquid water increase in the OCS of scattering particles decrease in visibility (minutes to hours). The hydroscopic growth resulting from cooling can occur at the surface or aloft. Haeffelin et al RH Visibility (m) β can be used to track progressive hygroscopic growth of aerosols over a sufficiently deep vertical profile. 8

9 PARAFOG: methodology Hygroscopic function used by PARAFOG: f RH = Time (resolution 1min) Rate of change of hygroscopic growth used by PARAFOG: 9

10 PARAFOG: methodology Hygroscopic function used by PARAFOG: Strong correlation between f RH and the Hänel function demonstrates the influence of the hygroscopic growth on β Hänel function: f RH = SIRTA site: γ parameters ranging from 0.24 to

11 PARAFOG: alert levels Thresholds < f βatt t OR Threshold <β att PARAFOG activation Several threshold values define a level of fog warning Fog alert levels PARAFOG is activated only when RH > 85 % and the cloud cover fraction < 50 % during at least 10 min. 11

12 Outline Introduction PARAFOG: description PARAFOG: fog cases analysis PARAFOG: its uses in practice Conclusions 12

13 PARAFOG: fog cases analysis For sites close to each other and under the same synoptic conditions: PARAFOG highlighted difference in fog formation. Uccle (suburban) Diepenbeek (rural) The urban site is subject to higher turbulence near the surface due to surface heterogeneities more difficult to reach supersaturated conditions at the surface. 13

14 PARAFOG: fog cases analysis All fog alert levels occur generally lower than 100 m but not at the same height for each site (environmental conditions) SIRTA (~ 20km city center of Paris): Uccle (~ 5km city center of Brussels): Haeffelin et al Time before fog (min) Time before fog (min) 14

15 PARAFOG: fog cases analysis PARAFOG applied also on ALC datasets of airports (Zurich, Vienna, Munich, Roissy) Vienna Munich Shallow fog Deep fog Deep fog 15

16 PARAFOG: fog cases analysis The number of alert levels before fog occurrence is different between each sites (environmental conditions) Vienna: 23 fog cases Munich: 23 fog cases Lhuisset A Altitude (m) Altitude (m) Depending on type of radiation fog: thick or shallow fog 16

17 Outline Introduction PARAFOG: description PARAFOG: fog case studies PARAFOG: its uses in practice Conclusions 17

18 PARAFOG: its uses in practice Many fog alerts at any given height or time step more precision needed to get high hit rate and low false alarms fog alarm: N alerts occur in 30 min x 100 m time/height window How many fog alerts are necessary to define a fog alarm? 200 Vienna: 19 fog cases (N >30) Vienna: 19 fog cases (N >10) Thick fog 175 Lhuisset A h -2h30-2h -1h30-1h -30 min fog +30min Time Too restrictive 0-3h -2h30-2h -1h30-1h -30 min fog +30min Time False alarms less filtered 18

19 PARAFOG: its uses in practice How many fog alerts are necessary to define a fog alarm? Vienna: 19 fog cases (N >20) Lhuisset A. N=20: 100% of alert levels is reached when fog occurs also the case for the others airport sites. 19

20 Shallow fog PARAFOG: its uses in practice Number of alert levels in favor of fog depending on the altitude where the hydroscopic growth occurs Munich: 23 fog cases (N >10) Lhuisset A h -2h30-2h -1h30-1h -30 min fog +30min Time Hydroscopic growth close to the ground not properly detected by ceilometer: number of alert levels are more occasional 20

21 PARAFOG: its uses in practice Test in real-time of PARAFOG (SIRTA-ROISSY) in parallel with the usual fog prediction methods. Test in real-time of PARAFOG on the 4 CL51 of RMI in collaboration with its weather office. 21

22 Outline Introduction PARAFOG: description PARAFOG: fog case studies PARAFOG: its uses in practice Conclusions 22

23 Conclusions - β measured with ALC can be used as a proxy to track aerosol backscatter coefficient hygroscopic growth. - PARAFOG highlights the evolution of the vertical structure of fog formation depending on environmental conditions of site. - PARAFOG is a new decision support useful for the fog forecast in near-real time as a complement to other fog forecast methods. - Further analyses should be carried out to test and to improve the performance of PARAFOG Reference: Haeffelin et al.: Radiation fog formation alerts using attenuated backscatter power from automatic lidars and ceilometers, Atmos. Meas. Tech., 9, ,

24 Thank you We are grateful to the data providers from 4 airports (Meteo- France: Roissy; DWD: Munich; Meteoswiss: Zurich and Austro Control: Vienna)