AGCD/AWRA time alignment #27
Description
From the AWRA v7 technical report (page 9):
The following notation is used for the climate forcing in the AWRA report:
- 𝑃𝑔 Daily gross precipitation to 9am local time (mm)
- 𝐾𝑑 Daily downwelling shortwave (solar) radiation midnight to midnight (MJ m–2 d–1),
- 𝑢2 Wind speed at a height of 2 m to 9am (m/s)
- 𝑝𝑒 Actual vapour pressure (Pa)
- 𝑇𝑚𝑖𝑛 Daily minimum air temperature to 9am local time (°C), and
- 𝑇𝑚𝑎𝑥 Daily maximum air temperature from 9am local time (°C)
AWRA-L calculates the water balance between 9 am of the day before to 9 am of its timestamp, predominantly to align with the observational (AGCD) period of rainfall. However, the (AGCD) minimum and maximum temperature of a given date corresponds to two differing 24-hour periods (the minimum value corresponds to the 24 hours before 9 am and the maximum temperature corresponds to the 24 hours after 9 am). Further, the solar measurements are the average values from midnight to midnight for a given date, with daylight predominantly aligning with the 24 hours ending 9am the following day. The actual vapour pressure is measured at 9 am and 3 pm, and we use a weighted average of these values to correspond to the day following 9am. As a result, when the AWRA system reads in the input data files times are shifted as follows to represent the 24 hours to 9am used to timestamp AWRA-L outputs:
• 𝑃𝑔 – as is (dated same as AWRA-L outputs)
• 𝐾𝑑 – shift forwards 1 day
• 𝑇𝑚𝑎𝑥 – shifted forwards 1 day
• 𝑇𝑚𝑖𝑛 – as is (dated same as AWRA-L outputs)
• 𝑢2 – as is (dated same as AWRA-L outputs)
• 𝑝𝑒 – shifted forwards 1 day
The shifting of 𝑇𝑚𝑎𝑥 and 𝐾𝑑 was implemented for the first time in AWRA-L v7 to fit with the 9 am to 9 am day.
UPSHOT: We should use these time shift when working with both AGCD and AWRA data files.