Póster presentado en: 27th ALADIN Workshop & HIRLAM All-Staff Meeting celebrado del 3 al 7 de abril del 2017 en Helsinki, Finlandia

Martín Pérez, Daniel

Morales Martín, Gema

English

Agencia Estatal de Meteorología

Use of Ceilometer Data for Cloud ValidationDaniel Martin & Gema MoralesCeilometer Data             Cloud Base Height: The ceilometers give the instantaneous base height of up to 3 cloud layers. Maximum height: 6000 mAEMET Ceilometer NetworkAEMET Ceilometer Network• Type of Ceilometers: Vaisala CL31 (Wavelength: 910 nm)• Number of airports: 11 (Iberian Peninsula and Balearic Islands)• The ceilometers send data every 10 minutes to the AEMET headquarters• Main purpose is the aerosol detection• In collaboration with EUMETNET E-PROFILE programCLOUD ALGORITHM (applied to ceilometer data)Distribution of ceilometers in the network on the Iberian Peninsula and the Balearic IslandsLeft: Quick look of backscatter profile for a 12 hour periodRight: Instantaneous height of the 2 lower cloud layers measured by the ceilometer compared with model output.Cloud cover algorithmIn order to compare the model with the ceilometer data, it is needed to obtain the cloud cover and the cloud base height from them.  • Cloud cover calculation based on algorithm reported by Larsson and Esbjörn (1995) and Wauben• Uses cloud base height of the three layers (C1, C2, C3) and visibility (VV) of the last 30 min• Give data of last 10 minutes double weight• Parameter valid only if 75% of data is available• The total weight of clouds of the lower cloud layer given by the ceilometer (C1) determines the total cloud coverBackscatter profile: The signal returned from the atmosphere due to Rayleigh scattering or to the aerosol and cloud dropletsVertical Visibility: In case of precipitation or fog the ceilometer reports the vertical visibilityBackscatter from model             Backscatter profile from model data.The two main contributions to thebackscatter profile, apart from thesolid particle aerosol:• The Rayleigh scattering obtainedfrom the temperature and pressureprofiles.• The scattering by the cloud droplets.The liquid water content is used for it.Comparison of backscatter profiles, in red the one of the ceilometer and in blue the one obtained from model data. Difference in BL are due to aerosol.Cloud base heightThe model and the METAR consider the cloud base height as that of the lower layer covering more than 4 octas of the sky. The algorithm characteristics are:• Up to 4 layers can be obtained• In order to distinguish between two layers, the distance between them is fixed to be 250 m or 20 percent of the cloud base height.• The cloud base will be the one of the lower layer with more than 4 octas coverage.Biblio: Wauben, W.M.F., KNMI, Automatation of visual observations at KNMILarsson, B. and Esbjörn, E., 1995, SMHI, Cloud Cover Algorithm.CLOUD COVER. (Ceilometer vs. METAR)COMPARISON RESULTS (ceilometer vs. METAR)Comparison of the calculatedcloud cover from ceilometerdata with cloud cover fromMETAR.For cloud cover METARmessages only report:• FEW: 1 to 2 octas• SCT: 3 to 4 octas• BKN: 5 to 7 octas• OVC: 8 octas•Model verification of the cloud cover against the ceilometer and the METAR observations.•Period: 1 month. Dec 2016.•Model Cycle 40h11.•Number of stations:7•Monitor softwareCloud cover. Time plot comparison for the airports of Ibiza (LEIB) and Alicante (LEAL) for a 7 days period.CLOUD BASE HEIGHTTime plot comparing model (AIB) against METAR, SYNOP and Ceilometer observations.CLOUD COVER• The cloud base height calculated from the ceilometers has been used for model verification• Number of ceilometers considered:8• Model cycle: 40h11b5•Period of time: Dec 2016The algorithm seems to overestimate the cloud cover mainly for high coverage. HARMONIE VERIFICATIONDespite the lower bias for the ceilometerobservations, the stdv is higher than the stdvfor the METAR.Cloud base height. Similar results are obtained (METAR messages often take the height from ceilometer observation).The table on the right and the plots bellow show this agreement.Table showing the comparison of cloudcover observed by METAR andCeilometer for Dec 2016 and 9 airports.CLOUD BASE HEIGHT. (Ceilometer vs. METAR)Cloud base height. Time plot comparison (Ceilometer vs. METAR) for the airports of Ibiza (LEIB) and Alicante (LEAL) for a 7 days period.Cloud base height. Time plot Model-Ceilometer comparison for the airports of Ibiza (LEIB) and Alicante (LEAL) for a 7 days period.•For the cloud base height the model has a positive bias for every forecast length.•For heights over 1200 m. the bias becomes negative.•There is little dependence of the stdv with height.In general, the coastal locations have higher stdv and bias than the interior locations.CEILOMETROSMETARThe time plot shows that the modelseems to follow the cloud covergiven by the ceilometers closerthan the one obtained from METARmessages.CEILOMETERSOBS <50 <100 <200 <300 <600 <1000 <1500 <2000 <2500 >2500 TOTALMETAR<50 2 2 0 0 0 0 0 0 0 1 5<100 1 7 1 0 0 0 0 0 0 0 9<200 0 0 2 0 0 0 0 0 0 0 2<300 0 0 3 7 1 0 1 0 0 0 12<600 0 0 0 10 36 2 1 0 0 0 49<1000 0 0 0 10 24 66 3 3 1 2 109<1500 0 0 0 0 8 36 81 7 8 2 142<2000 0 0 0 1 3 3 18 14 2 0 41<2500 0 0 0 0 0 0 0 0 2 1 3>2500 0 0 0 0 0 0 0 0 0 0 0TOTAL 3 9 6 28 72 107 104 24 13 6 372CEILOMETERSMETAROBS 0 1 2 3 4 5 6 7 8 TOTAL0 0 0 0 0 0 0 0 0 01 0 76 0 0 28 0 36 0 37 1772 0 0 0 0 0 0 0 0 03 0 0 0 0 0 0 0 0 04 0 35 0 0 28 0 64 0 61 1885 0 0 0 0 0 0 0 0 06 0 2 0 0 9 101 0 198 3107 0 0 0 0 0 0 0 0 08 0 0 0 0 0 5 0 68 73TOTAL 0 113 0 0 65 0 206 0 364 748Use of ceilometer data for cloud validation27th ALADIN Workshop & HIRLAM All-Staff Meeting 2017Vertical VisibilityThe vertical visibility given by the ceilometers has been compared with the visibility given by the model and the one of the METAR for a single case.Fog at the airport of Huesca from Dec 10th until Dec 14th.Low clouds VisibilityThe time plot shows:•Vertical visibility from ceilometer is comparable with the METAR visibility•The visibility given by the model seems to be lower in most cases.CONCLUSIONS• The ceilometers are valid instruments for cloud verification due to the continuous operation, the distribution of the instruments and reliability of the measurements.• The basic ideas of the cloud cover algorithm applied to the ceilometer data seems to be appropriate, although some study is needed in order to correct the cases of overestimation.• The cloud base height verification of the model shows a positive bias in most of the cases, mainly on islands and coastal areas• The vertical visibility given by the ceilometers seems to be comparable to the one obtained with other instrumentation.• The visibility given by the model seems to be lower in most cases.• It must be taken into account that only one month verification has been done.

Use of ceilometer data for cloud validation

https://repositorio.aemet.es/bitstream/20.500.11765/7696/1/Poster_ASM2017_ceilometros.pdf

Use of ceilometer data for cloud validation

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