ITALIAN AIR FORCE METEOROLOGICAL SERVICE
AND
MÉTÉO FRANCE
UPDATING AND DEVELOPMENT OF METHODS FOR
WORLDWIDE ACCURATE MEASUREMENTS OF SUNSHINE
DURATION
WMO TECO, Brussels, Belgium, 16-18 October 2012
Vuerich Emanuele (IMS)
1
Objective
To provide the scientific community with the results of an all-seasons
bilateral inter-comparison on sunshine duration (SD) measurement
methods that has been recently conducted by the Italian
Meteorological Service (IMS-AF) and Météo France (MF) during
the period 2010-2012
Contents




Motivation and purpose
Procedures and methods
Data analysis and results
Conclusions
2
Motivation and purpose
1. Motivation
Need for cost-effective solutions with suitable accuracy for
the climatology and solar energy applications;
a transition from no-more-recommended SD methods to
methods with improved achievable accuracy;
a standardized calibration method for SD measurements is
not yet available and agreed in the community
need to verify the applicability of the CIMO Guide
requirements:
CIMO Guide
being SDPERIOD [h day-1] =ΣSDSUB-PERIODS if I ≥ ITHR = 120 W m-2 , than:
1.
2.
3.
a “threshold accuracy” of 20% is admitted ( I Є [96;144] W m-2 );
SD uncertainty should be ±0.1 h day-1
SD resolution should be 0.1 h
Are such requirements applicable?
3
Motivation and purpose
2. Intercomparison objectives
IMS and MF started a bilateral intercomparison that has been
carried out in two different climatological locations (Vigna
di Valle, Italy and Carpentras, France) to achieve the
following objectives:
• Primary. Evaluation of the daily achievable uncertainty of SD
measurements: pyranometric methods (global irradiance),1-minaveraged direct solar irradiance and network detectors.
• Secondary. Global use of a pyranometric method for SD by using
BSRN (Baseline Surface Radiation Network) data
(for time reason this secondary argument is not treated here: see Vuerich et al. –
TECO2012 and Morel et al. - BSRN meeting, Postdam, 1-3 August 2012)
4
Procedures and methods
1. Intercomparison references and instruments
Carpentras, France (2011)
Messrs Morel and Mevel at work
Reference:
Reference:
Pyrheliometer: Epply NIP
Instruments:
Pyranometer: K&Z CM11
Network SD sensor: C&S
recorder (burn method)
Pyrheliometer: K&Z CH1
Instruments:
Pyranometer: K&Z CM11
Network SD sensor: CE181
(scanning by optical fiber)
Primary reference: absolute TMI pyrheliometer (RRC Carpentras) 5
Procedures and methods
2. SD measurements methods (1/3)
Reference method (SDREF ): pyrheliometric method based on 1
second direct irradiance (I) measurements (to reduce the
uncertainty due to questionable sunshine minutes in case of using
1 minute averages of I)
SD using 1 min avg of I and applying the “threshold accuracy”
Three SD measurements by the pyrheliometer:
(1) SDpyrh 1m, minutes of SD if the 1 min average of I ≥ 120 W m-2;
(2) SDthr 96, seconds of SD if I ≥ 96 W m-2;
(3) SDthr 144, seconds of SD if I ≥ 144 W m-2;
Pyranometric methods by using global irradiance, G:
 Step Algorithm (SA): minutes of SD using 1-min averaged G compared
with a “rough” threshold (GTHR = 0.4 Go, with Go = I0 sin(h) ).
If G ≥ GTHR then SDSA = 1 minute,
otherwise SDSA = 0 minute
6
Procedures and methods
2. SD measurements methods (2/3)
 Carpentras method (Olivieri,1998) or Météo-France Algorithm (MFA):
minutes of SD through the measurement of 1-min averaged global
irradiance (G) compared with an accurate threshold value.
If G ≥ GSeuil then SDMFA = 1 minute,
otherwise SDMFA = 0 minute
where:
- GSeuil = Fc 1080 (sin(h))1.25 (model)
- h ≥ 3° (data filtering)
-Fc = A + Bcos(2πd/365)
with:
- Fc representing a fraction of global irradiance in clear
sky in mean conditions of atmospheric turbidity;
- h being the elevation angle of the sun in degrees;
- d being the day number of the annual sequence;
Carpentras, France (2009)
Messers Morel, Olivieri, Didier, Vuerich
Fc factor depends on the climatic conditions of the location and A,B coefficients can be
empirically calculated through a long term comparison with SD measurements by
means of a pyrheliometer. For Vigna di Valle and Carpentras: A=0.73 and B=0.06
7
Procedures and methods
2. SD measurements methods (3/3)
 Slob and Monna Algorithm (SM): algorithm to calculate daily SD
from the sum of 10 minutes SD which implies the use of 10 minutes
average of G and the use of its maximum and minimum values
during the 10 min interval. The procedure to apply the algorithm is
documented in the Annex of Chapter 8 of the CIMO Guide (WMO,
2008) and by Hinssen and Knap (2007).
 SD network detectors: SD sensors respectively operated by
the Italian Met Service (IMS) and Météo-France (MF)
radiation networks.
8
Data analysis and results
The data have been analyzed by:
- scatter plots of SDx versus
SDREF (where x is the measuring
principle used) with linear fits,
- dispersion plots of SD daily
differences (SDx – SDREF) with
normal distribution fits,
and by determing pertinent
parameters for estimating the
daily achievable uncertainty of
each method and the
applicability of CIMO guide
requirements
BIAS (trueness)
St.dev (precision, repeat)
R2 (goodness of fitting)
R2 (goodness of fitting)
Skewness (symmetry)
9
SDpyrh 1m
versus
SDREF
(SDpyrh 1s )
10
SDtrh96 and SDtrh144
versus
SDREF
(SDpyrh 1s )
11
SDSENSOR
CE181
(MF)
SDSENSOR
C&S
(IMS)
12
SDSM
versus
SDREF
(SDpyrh 1s )
13
SDSA
versus
SDREF
(SDpyrh 1s )
14
SDMFA
versus
SDREF
(SDpyrh 1s )
15
RESULTS (Carpentras)
CIMO Guide
target uncertainty
METHOD
SDREF (1s)
Uncertainty* [hday-1]
± 0.06
Npts [%] in range {-0,1 ; +0,1} [h/d]
/
SD pyrh1 min
± 0.27
76.9%
Threshold accuracy
± 0.42
Not applicable
CE181 sensor
MFA
(best G method)
SA
Slob&Monna
(Worse G method)
± 0.23
84.6%
± 0.73
37.5%
[-1.37; +1.71]
21.5%
[-1.41; +2.07]
17,4%
* Calculated at 95% of confidence level (normal distribution) , otherwise the
interval with the 95% of samples
16
RESULTS (Vigna di Valle)
CIMO Guide
target uncertainty
METHOD
SDREF (1s)
Uncertainty* [hday-1]
± 0.06
Npts [%] in range {-0,1 ; +0,1} [h/d]
/
SD pyrh1 min
± 0.29
74.8%
Threshold accuracy
± 0.45
Not applicable
C&S recorder
MFA
(Best G method)
SA
Slob&Monna
(Worse G method)
[-2.35; +1.69]
15.5%
± 0.88
31.7%
[-1.36; +1.68]
18.2%
[-1.45; +2.43]
13,8%
* Calculated at 95% of confidence level (normal distribution) , otherwise the
interval with the 95% of samples
17
Summary and conclusions
The SDREF must be calculated by 1s I instead of 1-min averaged I;
The achievable uncertainties of pyranometric methods are not
comparable with the CIMO Guide target uncertainty and the threshold
tolerance must be reviewed;
The CIMO Guide requirement is not an appropriate target for
routine operational measurements and should be reviewed;
The CIMO Guide should be reviewed for taking into account
additional algorithms for estimating SD (such as MFA) and for
updating the typical achievable uncertainty of those methods;
An IOM report on this bilateral intercomparison is expected very
soon for extensively providing the results and the achievements.
ET on II is investigating the possibility to organize a large and allseasons intercomparison for all classes of radiation instruments
in Europe with the cooperation of PMOD/WRC and sponsorship of
interested countries. Is the time to seriously think about that?
18
… any successful enterprise starts with a group photo and around table!
Italy and France
Contacts:
vuerich@meteoam.it
jean-philippe.morel@meteo.fr
19
Extra data analysis and results
Improvement and global use of MFA by BSRN data:
- Concept: MFA algorithm was also extended to nine BSRN stations by
using 1-min average global and direct irradiances for at least 4
consecutive years.
- Purpose: determination of the best set of A and B coefficient that
minimize the total relative error of SD over a long period of time
(years) and a method for an universal application of the MFA for
estimating SD from global irradiance at all latitudes.
- Technique: consists in an empirical method that permits to select the
A,B from the plot of the cumulative difference between the SD from
MFA and SD from 1 min average of direct irradiance (assumed as
reference because available from BSRN data).
- Results: recently presented at the BSRN meeting in Postdam, 1-3
August 2012.
20
C AB AU W (N L)
C U MU LATED (SD -Sdref)
2006-2009
A=0.77 B =0.05 and 0.06
24
20
16
12
hours
8
4
0
-4
-8
-12
-16
-20
BSRN STATION Latitude
B=0,05
B=0,06
MOMOTE
TAMANRASSET
-24
0
2006
365
2007
730
2008
1095
2009
years
1460
2010
TATENO
BOULDER
C AR PEN TR AS (France)
C U MU LATED (SD -Sdref)
2007-2010
A=0.77
B =0.05
CARPENTRAS
PAYERNE
24
PALAISEAU
20
CABAUW
16
TORAVERE
12
A
B
Err %
-2
22
36
40
44
47
48
0,67
0,77
0,73
0,67
0,71
0,75
0,75
0
0
0,05
0,06
0,05
0,06
0,04
-0,1
-0,2
-0,2
0,1
0,1
0,4
0,2
52
58
0,77
0,74
0,06
0,06
0,2
0,4
hours
8
4
0
-4
-8
-12
-16
-20
-24
0
2007
365
2008
730
2009
1095
2010
years
1460
2011
21