Dealing with Daylight Saving Time

In flux data analysis, it is common to compare the local site data with data from other sites that are in regional or global flux networks (eg. AmeriFlux, FluxNet, AsiaFlux). The issue of timestamp is important for such comparisons, and using a time stamp that adjusts for Daylight Savings Time (DST) complicates the comparison because DST is not applied in all regions.

Therefore, the consensus in the community is to use standard time without adjusting for DST.

In many LI-COR gas analyzers and systems, an internal clock keeps time in a manner that is independent of the local time. The instruments then use Time Zone Database (http://en.wikipedia.org/wiki/Tz_database) to convert the internal clock to local time. This local time is used for display and is also appended in the data file names. In the software interface for these products, you can set the clock to local time by choosing a time zone or selecting an offset to UTC (see Table 1). The former typically includes both standard time and daylight saving time, so the offset to UTC will change as daylight saving time kicks off. When an offset to UTC is selected, the clock will always set to be our local standard time since the offset is not affected by daylight saving time. In addition, if daylight saving time is not adopted in your area (e.g., China), either choosing a time zone or selecting an offset to UTC will work fine.

Table 1. Offsets from UTC for some regions.

Location	Time Zone with DST	Time Zone without DST
New York City, NY USA	US/Eastern	Etc/GMT + 5
Chicago, IL USA	US/Central	Etc/GMT +6
Paris/France	Europe/Paris	Etc/GMT - 1
Tokyo, Japan	Asia/Tokyo	Etc/GMT-9
Sydney, Australia	Australia/Sydney	Etc/GMT-10