Heat sum

The heat sum is the sum of certain temperature values within a defined period of time . The opposite is the cold sum .

The variable is mainly used in the geosciences climatology , meteorology and ecology , as well as construction and energy engineering . There are numerous more specific definitions, possibly within a certain corridor of temperature values ​​that excludes extreme minima and maxima (cumulative heat differences, cumulative heat anomaly).

purpose

In general, the climate is better estimated using the total heat than using the daily mean temperature or the daily course of the outside temperature , as is typically entered in the climate diagram of a location. In particular, it is better suited for assessing a year, since it makes statements about the course of the annual course of daytime temperatures, and is also suitable for assessing the character of a season or the vegetation period .

In addition, it can also be used to assess the extent of individual heat waves or cold spells.

The value is used particularly in agro-climatology to carry out vegetation- oriented climate classifications and to make phenological predictions. It is a reference point for predicting the maturity of agricultural products.

It is also important for heating technology because it allows an accurate estimate of the heating energy requirement .

Definitions

In general, a temperature value in ° C (or K ) or Anglo-American ° F is calculated for each day and added up over the days. In addition, there are often certain correction factors.

${\displaystyle W=\sum _{d_{1}}^{d_{2}}\lambda _{\mathrm {i} }\cdot t_{\mathrm {i} }}$

often: ${\displaystyle t_{\mathrm {i} }=t_{\mathrm {1,i} }-t_{\mathrm {2,i} }}$

The dimension of the heat and cold sum is temperature × time , generally with the unit of measurement degree day (Kd or ° Fd - which is also used as a term for the heat sum itself).

The heat sums are calculated in different ways, depending on the context in which they are considered. This means that results differ so much that they can hardly be compared with one another.

Common definitions are:

• Addition of the daily mean temperatures above a threshold value
  • Usual threshold values: 0 ° C, 5 ° C, 6 ° C, 7 ° C, and 10 ° C (these are guide values ​​from which the metabolism of plants in general becomes active)
  • at 5 ° C (the limit value of a vegetation day customary in Central Europe ), the annual value in mid-latitudes is typically around 1000-3000 degree days
• The growing degree-day there are definitions of simple heat total, since the beginning, or the beginning of vegetation , up to special weights to geographic location ; Days with temperatures above +30 ° C are also often left out here
• For the grassland temperature sum (GTS), the winter months are calculated reduced (cumulative corrected GTS)
• In the Austrian soil estimate : The total heat is obtained by adding up all 2 p.m. temperatures over the entire year, provided that the daily minimum was not below 5 ° C and the daily maximum was not below 15 ° C (the 2 p.m. temperature is more closely related to assimilation than the daily mean temperature)
• Formation of the hourly temperature sums, about 5 ° C, from the beginning of vegetation
• In building air conditioning, the heating degree days (G, also the number of degree days G _t , divided by the time interval) are calculated between an indoor heating target of 20 ° C and the daily mean temperature outside, and only counts the days above a heating limit of 15 ° C (G ₁₅ e.g. German VDI 2067 / DIN 4108 T6, VDI 3807) or 12 ° C (G ₁₂ for Austria, Switzerland, Liechtenstein), or a local heating period . The cooling degree hours are calculated in the same way .
• In the Italian DPR 412, the total heat is referred to as the difference to 20 ° C, including the temperatures below
• In the US, NASA's NCDC uses 65 ° F (18.3 ° C) as a base

In addition, the temperature anomaly is calculated by calculating the total heat in relation to the daily values ​​of a suitable comparison year or the long-term mean, and then dividing by the period duration in days examined. This zoned according to several threshold values ​​forms the basis of many climate classifications .

A simple heat sum without a difference (in which positive and negative degree values ​​cancel each other out), divided by the days, is the mean temperature:

${\displaystyle M={\frac {1}{n}}\sum _{n}t_{\mathrm {i} }}$... arithmetic mean

• Examples (colors cannot be compared with each other)
• 

  Netherlands: Diagram of degree days (measurement unknown, values ​​around 3000 degree days)

• 

  Tuscany: total T _med −20 ° C (<1000 to ≥3000 degree days)

• 

  USA: cooling degree hours, base 65 ° F (18.3 ° C, values ​​500 to 4000 cooling degree hours)

• 

  2003 heat wave : anomaly year 2003 to 2001

• 

  Cold wave 2012 : anomaly 25.1. – 1.2. (Reference oA)

Web links

Commons : Maps of heat sums  - collection of images, videos and audio files

Individual evidence

1. ↑ the zero point of the scale drops out when a difference is formed
2. ↑ common in the application, compare sizes such as running meters (actually "length") or height meters ("height difference in meters")
3. ↑ according to Otmar Harlfinger, Gerd Knees: climatography . Part 1 of the Climate Manual of Austrian Soil Estimation; Climate Department of the Austrian Soil Estimation, Wagner University Press, Innsbruck, 1999; also Volume 58 of communications from the Austrian Soil Science Society , Verlag ÖBG, 1999; Information in climate table ( memento of the original from August 28, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , tirol.gv.at 
4. ↑ Art. 1 (z) DPR 26 agosto 1993, n.412 Regolamento recante norm per la progettazione, l'installazione, l'esercizio e la manutenzione degli impianti termici degli edifici ai fini del contenimento dei consumi di energia, in attuazione dell ' art. 4, comma 4, della legge 9 gennaio 1991 , n.10 (doc, clisun.casaccia.enea.it)
5. ↑ James Owenby, Richard Heim, Jr., Michael Burgin, Devoyd Ezell: Maps of Annual 1961-1990 Normal Temperature, Precipitation and Degree Days. Climatography of the US No. 81 - Supplement # 3 ( online article with maps ( memento of the original from August 1, 2012 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , lwf.ncdc.noaa.gov)