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Marine Data Temporal ConceptsContents |
Background
Time Recording & Notation
This is covered elsewhere, in the article Date and Time Standards for Marine Data.
Synoptic Marine Data & Products
- The term "synoptic" is defined by Wikipedia (see below) as referring to "observations that give a broad view of a subject at a particular time." This concept seems quite simple, but due to the impracticality of actually making enough measurements of the whole earth, an ocean, or even a particular basin, simultaneously, to claim that a "broad view" has been obtained, necessary compromises are almost always made when using the term in the marine sciences.
- In meteorology, the term "synoptic scale...(also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometres" (see below). This pins down the size of the area under consideration, but retains the notion of simultaneous observations. Meteorologists achieve quasi-synoptic (meaning nearly synoptic) analysis on a global scale through the use of rapid data transmissions through dedicated systems, such as the Global Telecommunications System
- Satellite observations of the ocean surface (and indirectly its interior), where polar-orbiting satellites yield multiple "swaths" over the earth surface in a single day, provide very nearly synoptic views of many variables over a period of one to a few days. Instruments that are only nadir-looking (i.e. provide along-track measurements directly below the satellite) take longer to provide the "broad view", but the term quasi-synoptic is often applied just the same.
- The vast system of at-sea observations of the Global Ocean Observing System (GOOS), especially including the Argo profiling floats, is beginning to provide a quasi-synoptic, direct view of the ocean's interior.
- Of course, depending on the size of the area of interest, observational coverage for any parameter might indeed be "synoptic" at any given time depending on satellite orbits, ship and buoy presence, etc. We prefer to reserve the term for normal conditions and length scales approaching the meteorological community's definition.
Climatological Marine Data & Products
- Wikipedia defines "climatology" as "...the study of climate, scientifically defined as weather conditions averaged over a period of time" (see below), but then goes on to state incorrectly that it "is a branch of the atmospheric sciences." This definition is too limited to be of any practical value.
- Climatologies can portray both atmospheric and hydrospheric conditions, recorded by objective data (not simply narratives) and presented as averages, cumulative amounts or extrema, over time periods that are substantially longer than the best currently prevailing "synoptic" time scales. These longer times scales are quite specifically relevant to social, economic or operational activities.
- Average means either simple arithmetic averaging or perhaps more complex, weighted measures applied to intensive variables.
- Cumulative amount means the total measure of an extensive variable, such as rainfall or streamflow, over a stated time period.
- Extreme means the maximum or minimum value of an intensive variable, such as the highest temperature during the day.
- For meteorological climatologies, where the entire earth is usually analyzed synoptically every 6 hours, climatological measures over periods of a day, and all longer periods, would be considered climatologies. In fact there are weather climatologies based on year-days.
- For ocean climatologies, where the data gathering and synthesis currently requires days to weeks, climatological measures over periods of weeks to months, and all longer periods, would be considered climatologies. In fact there are some satellite oceanographic climatologies based on 8-day periods, but the shortest period in-situ data climatologies are based on months.
Types of Climatologies
There are two types of climatologies found in the literature and in online sources, but no formal nomenclature that we can find addresses the differences between them. We offer here a benign set of terms to meet the need, but request any reader who knows more information about them to set us straight.
- Long Term Measures - These are climatological measures of the data, accumulated in time bins of stated length (but not necessarily "long"), where all the bins are recurring, same-named periods. For example:
- Average of all January data, all years. Called a monthly climatology.
- Average total stream flow in January, all years.
- Average of all "spring months" (defined appropriately), all years. Called a seasonal climatology.
- Average of all July 4 data, all years. A rare example of a daily climatology, which only the weather services could accomplish.
- Maximum rainfall on July 4, all years.
- Running Measures - These are climatological measures of the data, accumulated in sequential time bins of stated length. For example:
- Average of all January 2007 data; average of all February 2007 data; average of all March 2007 data, and so on. Sometimes also called, improperly, a monthly climatology.
- Gulf Stream integrated volumetric flow in June 2009; GS flow in July 2009; GS flow in August 2009; etc.
- The "Summary of Day" data for every calendar day, chronicled by the World Data Center for Climate, Ashville, North Carolina.
Additional Resources
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Information about this article
Short title: Temporal Concepts
Description: This section of OceanTeacher covers the ways that time (year, season, month, day, etc.) is recorded in marine data, and the various types of time-anchored data products, ranging range from instaneous views to long-term averages
Expertise level: beginner
Author: Murray.Brown
Approval status: approved
Approved by: Murray.Brown
Last change: 2010-4-2
Subsection of: Marine Data Infrastructure
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