• Number of frost and ice days
• Number of summer days and tropical nights
• Extreme values during a specific period
  
• Exceeding specific limits (Percentile)
• Daily temperature range
• Heating degree day
• Warm and cold spell duration
• Growing season length

The number of frost days (FD) is the annual count of days when TN (daily minimum temperature) < 0^oC.

Let TN_ij be daily minimum temperature on day i in year j. Count the number of days where: TN_ij < 0^oC.

The Number of icing days (ID) is the annual count of days when TX (daily maximum temperature) < 0^oC.

Let TX_ijbe daily maximum temperature on day i in year j. Count the number of days where: TX_ij < 0^oC.

The number of summer days (SU) is the annual count of days when TX (daily maximum temperature) > 25^oC.

Let TX_ij be daily maximum temperature on day i in year j. Count the number of days where: TX_ij > 25^oC.

The number of tropical nights (TR) is the annual count of days when TN (daily minimum temperature) > 20^oC.

Let TN_ijbe daily minimum temperature on day i in year j. Count the number of days where: TN_ij > 20^oC.

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 TX_x be the daily maximum temperatures in month k, period j. The maximum daily maximum temperature each month is then: TX_xkj=max(TX_xkj)

Monthly maximum value of daily minimum temperature (TNx):

Let TN_x be the daily minimum temperatures in month k, period j. The maximum daily minimum temperature each month is then: TN_xkj=max(TN_xkj)

Monthly minimum value of daily maximum temperature (TXn):

Let TX_n be the daily maximum temperatures in month k, period j. The minimum daily maximum temperature each month is then: TX_nkj=min(TX_nkj)

Monthly minimum value of daily minimum temperature (TNn):

Let TN_n be the daily minimum temperatures in month k, period j. The minimum daily minimum temperature each month is then: TN_nkj=min(TN_nkj)

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 TN_ij be the daily minimum temperature on day i in period j and let TN_in10 be the calendar day 10^th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TN_ij < TN_in10.

Percentage of days when TN > 90th percentile (TN90p):

Let TN_ij be the daily minimum temperature on day i in period j and let TN_in90 be the calendar day 90^th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TN_ij > TN_in90.

Percentage of days when TX < 10th percentile (TX10p):

Let TX_ij be the daily maximum temperature on day i in period j and let TX_in10 be the calendar day 10^th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TX_ij < TX_in10

Percentage of days when TX > 90th percentile (TX90p):

Let TX_ij be the daily maximum temperature on day i in period j and let TX_in90 be the calendar day 90^th percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TX_ij > TX_in90

The daily temperature range (DTR) is defined as monthly mean difference between maximum temperature TX and minimum temperature TN: Let TX_ij and TN_ij be the daily maximum and minimum temperature respectively on day i in period j. If I represents the number of days in j, then:

DTR_j = ∑^I_i(TX_ij - TN_ij) / I

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.

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 > 90^th percentile.

Let TX_ij be the daily maximum temperature on day i in period j and let TX_in90 be the calendar day 90^th 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: TX_ij > TX_in90.

The cold spell duration index (CSDI) is defined as annual count of days with at least 6 consecutive days when TN < 10^th percentile.

Let TN_ij be the daily maximum temperature on day i in period j and let TN_in10 be the calendar day 10^th 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: TN_ij < TN_in10

The Growing season length (GSL) is the annual (1^st Jan to 31^st Dec in Northern Hemisphere (NH), 1^st July to 30^th June in Southern Hemisphere (SH)) count between first span of at least 6 days with daily mean temperature TG>5^oC and first span after July 1^st (Jan 1^st in SH) of 6 days with TG < 5^oC.

Let TG_ij 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: TG_ij > 5^oC and the first occurrence after 1^st July (1^st January in SH) of at least 6 consecutive days with: TG_ij < 5^oC.

• http://cccma.seos.uvic.ca/ETCCDI/list_27_indices.shtml

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