Historical and Homogenized surface wind speeds for Canada
Update to December 2006
Background
A database of homogenized and long-term surface wind speeds (standard 10m level) has
been specifically designed for climate change analyses over Canada. The data consist of
hourly surface wind speeds after anemometer height adjustment and homogenized
monthly mean surface wind speeds for 117 stations across the country. Series start from
1953 or later and all the stations have at least 45 years of continuous observations. The
original data includes hourly surface wind speeds extracted from the National Climate
Data Archive of Environment Canada (element code is 076 at National Archives). There
is no joined station in this database. There are two steps used to homogenize surface wind
speeds. First, metadata and logarithmic wind profile are used to adjust hourly wind
speeds measured at non-standard height to the standard 10m level. Then, the monthly
mean wind speed series are derived from the anemometer height adjusted hourly wind
speeds and tested for homogeneity by a statistic inhomogeneity model based on
regression models (Wang, 2008), using homogeneous monthly mean geostrophic wind
speed series as reference series (which were derived from homogenized hourly sea level
pressure data recorded at Canadian and US stations). The methodology involves the
identification of imhomogeneities in the wind speed series, which are often non-climatic
steps due to station alterations including changes in anemometer height, in site exposure,
location, instrumentation, anemometer type, or a combination of the above. Monthly
adjustments were derived from the results of statistical tests/modeling, and the monthly
mean wind speeds were adjusted to the most recent segment (Wan et al., 2009). Hourly
data were only derived from the logarithmic wind profile and metadata for wind speeds
observed from non-standard height to standard 10m level. Whenever possible, the main
causes of the identified inhomogeneities from statistical tests were retrieved through
metadata database. For more information, please contact Judy Wan at Hui.Wan@ec.gc.ca.
Naming convention and file format for monthly homogenized surface wind speeds
Filenames are mws9999999.txt for monthly mean wind speeds and 9999999 represents
the 7-digits station identification number. These files are grouped together by province
and territories following the naming convention ws_mly_zz.zip where “zz” is the
abbreviation for the province or territory.
Within each file, the first line outlines the station characteristics (climate identification
number, name, province, element, unit, last update). The second line identifies the
content of each column (Year, Jan. to Dec., Annual means (Jan. to Dec.), seasonal means:
Winter (DJF), Spring (MAM), Summer (JJA), and Autumn (SON)). Each wind speed
value is followed by its respective flags. The record format is: i4,a1,17(f7.1,a1,a1,a1).
The data are in a comma-delimited format, which can easily be retrieved by packages
such as Excel. Missing values are identified as "-9999.9". The data flags are as follows:
"M" indicates a missing value, and "a" a value that has been adjusted due to homogeneity
assessment. The absence of a flag indicates an original, unaltered value.
Naming convention and file format for hourly adjusted wind speeds observed from
non-standard anemometer height to 10m level
Filenames are hws9999999.txt for hourly wind speeds and 9999999 represents the 7digits station identification number. These files are grouped together by province and
territories following the naming convention ws_hly_zz.zip where “zz” is the abbreviation
for the province or territory.
Within each file, the first line outlines the station characteristics (climate identification
number, name, province, element, unit, last update). The second line identifies the
content of each column with the data appear as year, month and day followed by 24
hourly values (the 24 entries represent the observations taken on the hours 00-23 at local
standard time) with their flags. The record format is i4,2(i4),24(f7.1,a1). Missing values
are identified by "-9999.9". The data flags are as follows: "M" indicates a missing value
and "a" a value that has been adjusted due to data observed from non-standard
anemometer height or has been set to missing value due to data failure of QC check . The
absence of a flag with any datum indicates an original and unaltered value.
REFERENCES
Wan, H., X. L. Wang, V. R. Swail, 2009: Homogenization and trend analysis of
Canadian near-surface wind speeds. To be submitted.
Wang, Xiaolan, 2008: Accounting for autocorrelation in detecting mean-shifts in climate
data series using the penalized maximal t or F test. J. Appl. Meteor. Climatol., 47
(No. 9), 2423-2444.