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Charts - Misc charts: Difference between revisions
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== Temperature Sum ==
This is a chart displaying a curve for every year with data from the first of January. So an incomplete first year of your series will not be displayed as data starting halfway a year have no meaning. This chart obeys the parameter [[Charts#MaxNrOfSeriesVisibileInGraph|MaxNrOfSeriesVisibileInGraph]]. The unit for the temperature sum is ''degree days''.
The graph represents the equation <math>\sum_{day=1}^{365} {(Average\ Temperature)}</math> for every <math>[(Average\ Temperature) > 0]</math>.
== Growing Degree Days ==
This is a chart displaying a curve for every year with data from the first of January. So an incomplete first year of your series will not be displayed as data starting halfway a year have no meaning. This chart obeys the parameter [[Charts#MaxNrOfSeriesVisibileInGraph|MaxNrOfSeriesVisibileInGraph]]. The unit for the temperature sum is ''degree days''.
There is a parameter [[Charts#GrowingDegreeDaysReferenceTemp|GrowingDegreeDaysReferenceTemp]] which represents the temperature at which plants start growing after winter rest. Then the graph represents the equation <math>\sum_{day=1}^{365} {(Average\ Temperature - GrowingDegreeDaysReferenceTemp)}</math>.
The reference temperature has a default of 5 °C which has it's origin in Finland and Sweden. You may adjust it to your own climatological and vegetal local situation.
See also this [https://en.wikipedia.org/wiki/Growing_degree-day wiki page], the paragraph below on ''Clash of Averages'' and beware the difference between a definition of an integral and an estimator for an average to use for calculation.
== Daily EVT (Evapotranspiration) ==
This chart only is valid when your weather station supports evapotranspiration. Currently that is only with the Davis stations with a solar sensor (optional). The calculation of the evapotranspiration is done by the station hourly ([https://www.davisinstruments.com/product_documents/weather/app_notes/AN_28-derived-weather-variables.pdf described here] - pdf) and the daily sum is reported by ''CumulusMX'' in [[Dayfile.txt|the Dayfile]] (field 24). This field is reported in this chart as a column chart. It also shows a moving average with a period as defined in [[Charts#PeriodMovingAverage|PeriodMovingAverage]].
The science around evapotranspiration is not only about weather variables, it is also much about the vegetation and the way plants use water. That may be very different in different climate zones as some plants are able to retain water by closing their stomata. Also forests have very different evaporation characteristics then open or half open fields. So in general, take care with this chart as it definitely has no absolute meaning nor heuristic that goes with it. It does however give a general view of the water condition and could be used as an heuristic itself to determine start of artificial raining (water gift)
== Monthly EVT (Evapotranspiration ==
This chart shows the evapotranspiration - see previous chart for explanation - per month for every year. The years have a different colour according to [[Charts#Colours|the colour scheme]]. The number of series directly visible is governed by the parameter [[Charts#MaxNrOfSeriesVisibileInGraph|MaxNrOfSeriesVisibleInGraphs]].
== Clash of Averages ==
At least two times there was a discussion on the forum about the way the daily average for temperature was or should be calculated (see [https://cumulus.hosiene.co.uk/viewtopic.php?p=138513#p138513 here] and [https://cumulus.hosiene.co.uk/viewtopic.php?p=152909#p152909 here]). CumulusMX uses and ''integration method'' which means it samples the temperature continuously at the sampling frequency and stores the average of those samples at the logging frequency. It creates the sum of the logged entries and at the end of day it divides them by the number of observations giving the arithmetic average of all values logged which acts as an estimator of the physical average.
Apparently the Meteorological Service of Britain does it still differently and does not use automatic measurement but takes manual readings twice a day and creates the daily average by <math>(Max+Min)/2</math> () and as argument it is that comparison with observations from before the computer era must be made. Note that the KNMI (the Dutch Meteorological Service) takes hourly measurements so there is no consistency between countries to start with.
As an argument in this discussion this chart was made to make the difference between the institutional method and the Cumulus Integral Method visible. What is shown is the Cumulus Method Daily Average Temperature: <math>(\sum_{minute=1}^{1440} {(Temp\ measurement)) \div 1440}</math>, the <math>(Max+Min)/2</math> and the difference between the two. It is clear that the first is the more accurate estimator than the two sample estimator (note they both are estimators for the statistic <math>average</math>).
The difference has a pretty even distributed noise around the zero line so comparison with current ''integral'' with observations from the past (for climatic studies) should be possible and a consolidation of past and current measurements has actually been executed by the KNMI (reference?).
[[Category:CumulusUtils]]
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