INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
Manuel Carvajal
National Institute of Meteorology and Hydrology – INAMHI
Innaquito St. N36-14 and Korea St.
Quito – Ecuador
Telephone: (593-2) 397-1100
Telefax: (593-2) 2244-407
Web site: www.inamhi.gov.ec / inamhi@inamhi.gov.ec
e-mail: mcarvajal@inamhi.gov.ec
manocarv@yahoo.com
ABSTRACT
Introduction
Preliminary Inter comparison data between Conventional station and automatic station ("Logotronic"),
installed in a location at 3100 m. a.m.s.l. (Izobamba – Ecuador)
Rainfall data
Pluviograph registered a higher value than rainfall sensor. The differences keep certain condition in
rainfall quantity: with low values (less than 1.0 mm) is -0.08 mm; between 1.1 and 5.0 mm is -0.22;
from 5.1 to 10.0 mm is 0.57 and over 10.1 mm is -1.07 mm.
Extreme temperatures
Maximum Temperature Data; Maximum thermometer registered superior values than temperature sensor.
In 69% of registered data the differences are more than 0.5 ºC
Minimum Temperature Data; Minimum thermometer registered lower values than temperature sensor. In
40 % of registerd data the differences are more than 0.5 ºC.
Relative Humidity Data
Sometimes is lower and sometimes is higher between conventional instrument and automatic sensor. In
42% of registered data the differences fluctuate among - 5 to - 15%, but in the 58% of data is lower
than 5%.
INTERCOMPARISON DATA BETWEEN AUTOMATIC STATION AND CONVENTIONAL
(IZOBAMBA-2009)
Introduction
In July 2009 inside Izobamba station was settle an automatic station (“Logotronic), so it was necessary
to analyze of data given by both stations.
Parameters and period of analysis
The meteorological data compared were: rainfall, temperature and relative humidity from 10 th July to 31st
December/2009. The automatic station was set up to register rainfall every 5 minutes and the other
parameters every 10 minutes. The data from conventional weather station is registered five times per
day 12z, 15z, 18z, 21z and 24z.
Data Processing

To select data from automatic station in the same time that schedules of conventional station.

Total daily precipitation (automatic and conventional)

Temperature extreme values.

Relative humidity extreme values.

Temperature and Relative Humidity daily averages.

Graphs of: rainfall, extreme and averages temperatures and relative humidity.

Comparative table.

Conclusions and Recommendations
Rainfall inter comparison
Unfortunately the rainfall data was very low during the study, this could make that data have a low
difference from daily and total values, it would change if the rainfall was similar or over normal values.


13th August automatic station gave 2.4 mm and conventional station doesn’t show values, it was
testified by pluviograph register.
In December the most representative differences were similar or bigger than 1.0 mm (7th, 8th,
18th and 21st).
1

October, November and December the rainfall was more representative than the previous months,
many differences were detected 8.4, 5.0 and 5.3 mm respectively.
Inter comparison of maximum temperatures

The conventional station registered bigger values than automatic station with a variation between
0.1 and 1.9 ºC (November 24th).

From 174 data, 23.7 % the difference is less than 1.0 ºC, 45.3% is higher than 0.5º C but lower
than 1.0 ºC, and 31 % is similar or lower than 0.5 ºC.
Inter comparison of minimum temperature

The conventional station registered lower values than automatic station with a variation between
0.1 and 2.4 ºC (November 23rd).

From 174 data, 11.5 % the difference is more than 1.0 ºC, 28.7 % is higher than 0.5º C but
lower or similar than 1.0 ºC, and 59.8 % is lower than 0.5 ºC.
Inter comparison of mean temperature

The difference between mean temperature values is very low and has positive and negative
values.

Only 5.4 % the difference is bigger than ±.0.5 ºC, the most of data (94.6 %) variation is smaller
than 0.5ºC.
Inter comparison of mean relative humidity

The variations in every month are remarkable. November and December has positive and
negative differences. The values of relative humidity from conventional station are bigger than
given by automatic station.

A big variability between both stations, with negative (- 1 to -15 %) and positive (1 and 3 %),
when the difference is over the threshold of 5 % the values are not reliable.

The table Nº 1 shows values with low differences from October to December, the variation from
July to September is bigger than the maximum permissible.
JUL
AUG
SEP
OCT
NOV
DEC
Auto Conv Auto Conv Auto Conv Auto Conv Auto Conv Auto Conv
Max
Diff
Min
Diff
97
97
99
0
29
40
-11
30
Width
68
69
57
98
97
96
99
36
1
22
33
-11
33
75
66
1
-6
62
63
98
100
36
32
1
100
100
34
42
0
-3
0
-2
62
68
100
40
2
66
58
60
About rainfall
The table Nº 2 shows the total rainfall of every month, the total difference is 20.4 mm, is a great value if
we consider that difference in a place with scarce precipitation or inclusive in other with high values.
Month
July
August
September
October
November
December
Total




Automatic
(mm)
5.2
28.9
9.0
78.1
75.3
77.0
273.5
Conventional
(mm)
6.2
29.0
9.6
86.5
80.3
82.3
293.9
Difference
(mm)
1.0
0.1
0.6
8.4
5.0
5.3
20.4
Conventional station registered bigger values than the automatic one.
Differences vary among - 0.1 mm in August until - 5.3 mm in December. Total variation is equal
to 20.4 mm.
There is certain correspondence with the amount of rainfall: less than 1.0 mm the difference is 0.08; between 1.1 and 5.0 mm the difference is -0.22; when the rainfall reach values between
5.1 to 10.0 mm the variation is - 0.57 and rains over 10.1 mm the difference is - 1.07 mm.
Would be interesting to analyze rainfall when the values are similar to normal or will be better in
extreme events.
2
About




maximum temperatures:
Conventional station values are frequently superior than automatic.
The difference average is between - 0.72 and - 0.86 ºC.
69% of data has a difference bigger than 0.5 ºC.
The maximum variation is 1.9 º C (November 24th).
About minimum temperatures:



Minimum temperature data of conventional station is frequently lower than automatic station.
Difference average between two stations is + 0.26 to + 0.65 ºC.
In 40.2% of data the difference is bigger than + 0.5 ºC. The maximum difference was 2.4 ºC
(November 23rd).
About mean temperature
The mean values of temperature in both stations are very similar, with differences lower than 0.5 ºC in
94.6% of data. The bigger difference was 1.4 ºC (October 5 th).
About mean of relative humidity

From July to October the average values of relative humidity are bigger in conventional station
than automatic one.

In November and December the differences are positive and negative, its mean that in occasions
the average of relative humidity in conventional station is superior and sometimes inferior to
automatic station.

42 % of data the differences fluctuate among – 5 and -15%, in 58 % the variation is ± 5% it
would be considered as an acceptable difference.
Conclusions and recommendations




The tendency in both stations is similar.
Significant difference analyzed data by data
A bigger period of time would be convenient in order to find similar o different variations.
Set up automatic station to register every 5 minutes for rainfall and every hour for temperature
and relative humidity would help to improve the data treatment and comparison.
INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
3
Total Rainfall inter comparison
Rainfall Variation (mm)
mm
90
80
70
60
50
40
30
20
10
0
Auto
Conv
July
August
September
October
November December
month
Example Rainfall Comparative Graph (Conventional/Automatic)
INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
Inter comparison of maximum temperatures
4
T.Maximum Variation (% )
24
31
> 1 ºC
45
Between 0,6 a 1 ºC
< = 0,5 ºC
Example Maximum Temperature Comparative Graph (Conventional/Automatic)
INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
Inter comparison of minimum temperatures
5
T. Minimum Variation (% )
11
29
60
> 1 ºC
Between 0,6 a 1 ºC
< = 0,5 ºC
Example Minimum Temperature Comparative Graph (Conventional/Automatic)
INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
Inter comparison of average temperature
6
Mean Temperature Variation (% )
5
> 0,5 ºC
95
< = 0,5 ºC
Example Average Temperature Comparative Graph (Conventional/Automatic)
INTER COMPARISON DATA BETWEEN AUTOMATIC WEATHER STATION AND CONVENTIONAL STATIONECUADOR
Inter comparison of Relative Humidity
7
Relative Humidity Variation (% )
42
58
Between - 5 a - 15%
< = 5%
Example Average Relative Humidity Comparative Graph (Conventional/Automatic)
8