6.6. Standards for Calculating Hourly, Daily and Annual Means
INTERMAGNET requires that all mean values be calculated using the rules described in the next sections.
6.6.1. Hourly Mean Values
The hourly mean values must be produced following the IAGA rules:
Arithmetic average of the 1-minute data
Centered on the center of the hour (HH:29:30, HH=hour) using 1-minute data 00-59 of the hour
6.6.2. Daily Mean Values
The daily mean values must be produced using the following rules:
Arithmetic average of the 1-minute data
Centered on the center of the day (11:59:30) using 1-minute data 00:00-23:59 of the day
6.6.3. Annual Mean Values
The annual mean values must be produced using the following rules:
Arithmetic average of the 1-minute data
Centered on the center of the year (02 July 11:59:30 for a regular year, 01 July 23:59:30 for a leap year) using 1-minute data 01 January 00:00- 31 December 23:59 of the year
6.6.4. Rule for Missing 1-minute Values
When mean values are to be calculated the question of how to handle missing data arises. For a number of reasons it is difficult to devise a simple objective rule that can be applied to all cases. INTERMAGNET recommends a simple and pragmatic approach: mean or filtered values may be calculated when 90% or more of the values required for calculation are available. This can be interpreted as either 90% of the values or 90% of the weight of the filter. When fewer than 90% of the required values are available the value should be assigned the value used to flag missing data.