Climate Indices of Air Temperature
- Number of frost days and ice days
- Number of summer days and tropical nights
- Extreme temperature values during a specific period
- Exceeding specific limits (Percentile)
- Daily temperature range
- Heating degree day
- Warm and cold spell duration
- Growing season length
Number of frost days and ice days
The number of frost days (FD) is the annual count of days when TN (daily minimum temperature) < 0oC.
Let TNij be daily minimum temperature on day i in year j. Count the number of days where:
TNij < 0oC.
The Number of icing days (ID) is the annual count of days when TX (daily maximum temperature) < 0oC.
Let TXijbe daily maximum temperature on day i in year j. Count the number of days where:
TXij < 0oC.
Number of summerdays and tropical nights
The number of summer days (SU) is the annual count of days when TX (daily maximum temperature) > 25oC.
Let TXij be daily maximum temperature on day i in year j. Count the number of days where:
TXij > 25oC.
The number of tropical nights (TR) is the annual count of days when TN (daily minimum temperature) > 20oC.
Let TNijbe daily minimum temperature on day i in year j. Count the number of days where:
TNij > 20oC.
Extreme temperature values during a specific period
Extremevalues are here defined as maxima and minima values of the maximum and minimum temperature. The following four cases are defined:
Monthly maximum value of daily maximum temperature (TXx):
Let TXx be the daily maximum temperatures in month k, period j. The maximum daily maximum temperature each month is then:
TXxkj=max(TXxkj)
Monthly maximum value of daily minimum temperature (TNx):
Let TNx be the daily minimum temperatures in month k, period j. The maximum daily minimum temperature each month is then:
TNxkj=max(TNxkj)
Monthly minimum value of daily maximum temperature (TXn):
Let TXn be the daily maximum temperatures in month k, period j. The minimum daily maximum temperature each month is then:
TXnkj=min(TXnkj)
Monthly minimum value of daily minimum temperature (TNn):
Let TNn be the daily minimum temperatures in month k, period j. The minimum daily minimum temperature each month is then:
TNnkj=min(TNnkj)
Exceeding specific limits (Percentile)
To avoid possible inhomogeneity across the in-base and out-base periods, the calculation for the base period (1961-1990) requires the use of a bootstrap processure. Details are described in Zhang et al. (2004). The results include the percentage of days with
Percentage of days when minimumtemperature TN < 10th percentile (TN10p):
Let TNij be the daily minimum temperature on day i in period j and let TNin10 be the calendar day 10th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where:
TNij < TNin10.
Percentage of days when TN > 90th percentile (TN90p):
Let TNij be the daily minimum temperature on day i in period j and let TNin90 be the calendar day 90th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where:
TNij > TNin90.
Percentage of days when TX < 10th percentile (TX10p):
Let TXij be the daily maximum temperature on day i in period j and let TXin10 be the calendar day 10th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where:
TXij < TXin10
Percentage of days when TX > 90th percentile (TX90p):
Let TXij be the daily maximum temperature on day i in period j and let TXin90 be the calendar day 90th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where:
TXij > TXin90
Daily temperature range
The daily temperature range (DTR) is defined as monthly mean difference between maximum temperature TX and minimum temperature TN: Let TXij and TNij be the daily maximum and minimum temperature respectively on day i in period j. If I represents the number of days in j, then:
DTRj = ∑Ii(TXij - TNij) / I
Heating degree days
The so called heating degree days (HDD) are a measure for the energy needed for heating an days at which the temperature falls below a defined limit. A typical value for this limit is an ambient temperature of 17°C. The related heating degree days (HD17) are the temperature sum of 17°C minus temperature of day with Tmeparature
T < 17°C.
Warm and cold spell duration
Indices are defined for duration of cold and warm periods.
The warm spell duration index (WSDI) is defined as Annual count of days with at least 6 consecutive days when TX > 90th percentile.
Let TXij be the daily maximum temperature on day i in period j and let TXin90 be the calendar day 90th percentile centred on a 5-day window for the base period 1961-1990. Then the number of days per period is summed where, in intervals of at least 6 consecutive days: TXij > TXin90.
The cold spell duration index (CSDI) is defined as annual count of days with at least 6 consecutive days when TN < 10th percentile.
Let TNij be the daily maximum temperature on day i in period j and let TNin10 be the calendar day 10th percentile centred on a 5-day window for the base period 1961-1990. Then the number of days per period is summed where, in intervals of at least 6 consecutive days: TNij < TNin10
Growing season length
The Growing season length (GSL) is the annual (1st Jan to 31st Dec in Northern Hemisphere (NH), 1st July to 30th June in Southern Hemisphere (SH)) count between first span of at least 6 days with daily mean temperature TG>5oC and first span after July 1st (Jan 1st in SH) of 6 days with
TG < 5oC.
Let TGij be daily mean temperature on day i in year j. Count the number of days between the first occurrence of at least 6 consecutive days with: TGij > 5oC and the first occurrence after 1st July (1st January in SH) of at least 6 consecutive days with:
TGij < 5oC.
References
This information is taken from:
http://etccdi.pacificclimate.org/list_27_indices.shtml
The following references are given there:
- Karl, T.R., N. Nicholls, and A. Ghazi, 1999: CLIVAR/GCOS/WMO workshop on indices and indicators for climate extremes: Workshop summary. Climatic Change, 42, 3-7.
- Peterson, T.C., and Coauthors: Report on the Activities of the Working Group on Climate Change Detection and Related Rapporteurs 1998-2001. WMO, Rep. WCDMP-47, WMO-TD 1071, Geneve, Switzerland, 143pp. (pdf, not barrier-free)