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Since the late 1960s, temperature measurements
have been made over extensive areas of the five Atlantic Provinces
(New Brunswick, Newfoundland, Nova Scotia, Prince Edward Island and
Quebec). Data from this program, collectively known as the Long Term
Temperature Monitoring Program (LTTM) have been collected by the Bedford
Institute of Oceanography, Institut Maurice Lamontagne and Northwest
Atlantic Fisheries Centre.
Instrumentation
The temperature recorders used to collect the data
have changed throughout the duration of this program. Throughout most of
the 1980s a mechanical strip chart recorder with an oil filled piston
temperature sensor (Ryan thermograph) was used. These instruments are
accurate to no better than 0.5°C. The data were manually
digitized and interpolated to a sampling frequency of four hours.
Digital instruments (Hugrun, Vemco, Hobo) with
accuracy in the range of 0.1 - 0.3°C were introduced in
the late 1980s and used exclusively by 1993. Sampling rates for these
instruments is typically 30 minutes to 2 hours.
Analysis
The NAFO fishing areas were used as a basis for
defining the statistical regions. All data were obtained from the
Coastal Time Series database (CTS) which is a publicly accessible
Internet database. (
http://www.mar.dfo-mpo.gc.ca/science/ocean/database/data_query.html).
CTS contains daily temperature statistics (daily mean, minimum and maximum)
for approximately 3500 time series from the program's inception to 2000.
Initially all of the time series within a NAFO area for a depth of <12
metres were combined to form a single daily time series. Individual
stations were examined to determine their suitability for inclusion in the
analysis since CTS contains series that are well offshore as well as in
rivers. Since the objective is to create a time series that represents the
nearshore conditions for the open coastline, offshore and river series were
removed. The remaining individual observations were averaged where more
than one series existed for the same day. The single daily series was
then averaged to form a monthly series over the entire observation period,
which in turn was averaged over all months to determine climatological
statistics for each month. All of this averaging can result in some confusion
over what the numbers actually represent. An explanation of how each number
was derived is given in the next section.
Individual series - The contents of CTS,
and the basis for this analysis, is a set of daily average temperatures
for each deployment of a thermograph. The average is based on between
6 and 48 individual observations, depending upon the sampling interval
of the instrument. Instruments in the early years of the program were
digitized at a sampling rate of 4 hours. Recent instrumentation typically
samples every 30 minutes to hourly.
Daily Series - The daily series consists of
the daily mean, minimum and maximum temperatures of all the individual
series within an area. The daily mean temperature is the average of all
mean values in the individual series. The daily maximum is the maximum
value of all the individual daily maximum values. The daily minimum is
calculated in the same manner.
Monthly Series - The monthly series consists
of the monthly mean and the minimum and maximum values of the daily series.
The monthly mean is the average of all the daily average temperatures from
the daily series within a given month. The monthly maximum is the maximum
value of all the individual daily mean values. There will be
individual (hour to four hour) observations outside of the minimum and
maximum values.
Annual Cycle - The annual cycle is the final
stage of the analysis and the one that is reported. The monthly mean
value is the average of all of the mean values for a particular month. In
many cases this would be based on 10 or more years where a particular month
had data. Each individual month is given the same weight in the average,
so that a monthly average based on many individual series will not dominate
a monthly average based on only one series.
Summary Statistics
Each area includes monthly climatological
statistics for;
- Minimum temperature - minimum daily average temperature from an
individual series
- Maximum temperature - maximum daily average temperature from an
individual series
- Mean temperature - mean value for a given month based on the
monthly mean values for an individual month
- Standard deviation - Standard deviation is a measure of how variable
the temperature is within a month. About two-thirds of the measurements
would lie within 1 standard deviation from the mean. The standard
deviation is based on the individual monthly values used to calculate
the mean.
- Years - number of years which had data for a given month.
- Total Observations - total number of "data days" from
individual series for a given month
Number of Observations in 2°C Ranges
The second table shows the distribution of daily
averages from individual series grouped within 2°C
ranges from -4°C to 24°C. This gives an indication
of how likely it is of getting an extreme value within a particular month.
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