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Meteorological day: Difference between revisions
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{{Version badge Mx}}{{Version badge 1}}This page applies to both the original Cumulus software and MX.[[Category:Terminology]]
=Traditionally=▼
The modern Cumulus user tends to forget that computerisation is a fairly recent change (in the last few decades) for weather recording, which has been taking place for at least a century in most nations.▼
Older people will remember how weather was traditionally recorded. Weather instruments were not directly connected to a computer. Observers would manually read the instruments at least once a day, traditionally at 9 a.m. (one hour later in daylight saving time). Some observers made measurements every hour, or more frequently at places like airports.▼
Certain instruments, like barographs and sun recorders, did record readings on a continuous process, but they still needed to be manually read and interpreted. For temperature, [[Temperature_(and_humidity)_measurement#James_Six_and_Diurnal_Variation_measurements|James Six]] invented an instrument that could store the highest and lowest temperatures between manual readings.▼
Measurements were manually logged onto a sheet, or into a notebook, as they were made. Subsequently, longer period derivatives could be calculated from the manual measurements and these might be either phoned to the main weather service, transmitted electronically (e.g. by telex), or entered into an electronic record.▼
=Modern era=▼
Towards the end of the 20th century, not only did computers become small enough to be located on a widespread basis, but electronic sensors that could record various weather parameters started to become cheap, reliable, and widely available.▼
Thus the concept of recording weather in real-time finally became available.▼
=Daily assignment=
The World Meteorological Office (WMO) allows individual nations some flexibility, and does not prescribe total international alignment. Thus the practice of UK Met Office, the Australian BOM, the Met organisations in New Zealand, Israel, Canada and the USA, each have differences that cannot be fully covered here (some get mentioned in forum posts, see [[#Read more]]).
Most weather organisations in the world still to some extent remain consistent with the traditional way of working. This means that they report by '''meteorological day'''.
Steve Loft created Cumulus software, back in 2003, because he owned a weather station and he could not find any software that allowed him to process measurements in the way he wanted. The first public release, allowing other people to use his software, was on 27th January 2004. Most weather software can only report daily measurments on a calendar day basis (since midnight). Steve Loft did make a simplifying assumption that does not align with the practice of most Meteorological Offices, as the table also indicates, he decided to design Cumulus software so it would report all daily derivatives based on a day that started at 9 a.m., he later added reporting since midnight for rain. MX development by Mark Crossley has added reporting rainfall maximums in any 24 hour period and reporting maximum and minimum temperature since midnight.
The legacy Cumulus made the swap to 10 a.m. in Daylight Saving time optional, and also permits the use of a midnight rollover as another option.
The following table tries to illustrate the divergence if you choose a rollover time other than midnight:
|-
! scope="row"| Rainfall
| Some nations report the daily rainfall for the 24 hours prior to the
| Cumulus checks the current reading from a "count" supplied by weather station, it subtracts
|-
! scope="row"| Sunshine Hours
| Always reported by calendar day (
| Regardless of which rollover time is selected, Cumulus always reports sunshine hours from one minute past midnight until exactly midnight for any day. Note, MX does this efficiently, by using [[yesterday.ini]] if necessary to store total at midnight; the legacy Cumulus 1 was dependent on internally (RAM) held counts, so
|-
! scope="row"| Snowfall
| Reported for day starting at selected rollover time
|-
! scope="row|
| Highest wind speed is reported, based on measurements involving averaging over 10 minutes, for day starting at 9 a.m. Gusts are highest speed reported in a 10-minute sample. [[Gale Days]] are reported for any day when for at least 10 minutes starting at midnight the sustained wind speed exceeds 39 mph (62 km/h, 34 kts) or more, equivalent to Beaufort F8 or above.
| Reported for day starting at selected rollover time
|}
==Choice of rollover time==
It has been mentioned that Cumulus allows for 3 rollover time choices:
# 9 a.m. throughout year (if timezone does not include daylight saving period, all days will be 24 hours long; otherwise there will be issues when clocks change to/from DST)
# 9 a.m. in winter, 10 a.m. when/if Daylight Saving Time applies (all days will be 24 hours long, throughout year; still will be issues when clocks change to/from DST)
# Midnight throughout year (if timezone does not include daylight saving period, all days will be 24 hours long; otherwise there will be issues when clocks change to/from DST)
Once you have made the choice of one of these rollover time settings, you will stick to that. If you make a change, then it is best to start with a new set of files in the [[data folder]] because the only unaffected file is '''all-time.ini'''.
Steve Loft did not ever share the code for Cumulus 1, but he did make some observations concerning his code. It appears some (but apparently not all) of his legacy code used a special time zone with a 9 a.m. rollover recording as if it was midnight on the date in question, i.e. the internal Cumulus clock was subtracting 9 hours from the computer clock; e.g. when a clock showed 3 p.m. the time stored by Cumulus (and this could be seen in certain tags that by default only showed date) was 06:00 on the date in question (not 15:00).
Cumulus MX consistently uses the clock time reported by whatever device is running the software; if that time is wrong for any reason, every action by MX will be recorded against wrong time, and possibly wrong date.
▲=Traditionally=
▲The modern Cumulus user tends to forget that computerisation is a fairly recent
▲Older people will remember how weather was traditionally recorded because there were a lot of local measuring stations, often located in places where they could be seen, like parks within settlements, roofs of public buildings, near public viewing points at airfields, or in fields on edges of smaller settlements.
▲
▲
▲=Modern era=
▲Towards the end of the 20th century, not only did computers become small enough to be located on a widespread basis, but electronic sensors that could record various weather parameters started to become cheap, reliable, and widely available. Also the invention of the teleprinter, and later of internet, provided ways of electronically sharing in near enough real-time.
▲Thus the concept of recording/sharing weather data in real-time finally became available.
Subsequently labour costs mean that in most nations, few physical weather stations remain, generally maintained only for two purposes. The first purpose is to serve the needs of pilots, most airfields continue to have local recording sensors, fully automatic at some airports, supplemented by manual observations at airports prone to fog or other issues of concern, and still manually operated at smaller airfields that have not invested in computerised kit. The second purpose is to provide consistency with past measurements where still used to inform climatological models based on measurements over 1 to 3 decades, this has preserved a few physical representational sites in each nation.
For all other locations, there is a reliance on satellites to sense the weather. National meteorological services use mathematical models to interpolate those widely spaced sensings to produce estimates of readings, and to make forecasts, for a more local grid based network of locations.
=Read more=
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