ICOADS Web information page (Wednesday, 11-May-2016 19:12:23 UTC):

Release 2.5 (Preliminary) sea level pressure (SLP) data continuity questions

Fig. 1 provides a 4-panel comparison plot between preliminary Release 2.5 data and Release 2.4 data (2° enhanced monthly summaries in both cases) for a selected 20-year focus period (for details on the 4-panel plot layout see icoads.noaa.gov/panels.html; note that a minimum of 1000 nobs are required per month, or all curves are omitted to ensure meaningful data patterns). The remaining plots explore some of the noteworthy data-difference patterns on a deck-by-deck basis for selected periods or subperiods.

Discussion
Note: "main" figure references are to the parent [Release 2.5 (Preliminary) Data Characteristics].

a. Fig. 1 shows generally positive SLP differences during 1910-29 (extending through 1930-33; ref. main Fig. 2f5), with the largest increases around 1915-19. The period around 1915-19 (see main Fig. 4b) is also when few new deck 762 ("Japanese Kobe Collection Data") were added (whereas many were for 1920-32). However, an important note is that Fig. 4b shows only overall increases or decreases in the numbers of reports per deck; it does not indicate when one version of a deck (as differentiated by a separate report field, source ID) has been replaced by another. For this update, we are fully replacing the Kobe Collection 1998 Edition with the 2003 Edition, and believe that the 1915-19 patterns result from SLP data improvements that Japan made in the 2003 Edition.
Proposed action:
None at this time.
b. Several other decks appear (see Fig. 2a) to have suspicious aggregate SLP distributions, but a number of these probably reflect geographic coverage (e.g., decks 187-188, 246, 736, 761, 897-899 are all likely to contain mostly high latitude, such as whaling and expeditionary, data). As a contrasting example however deck 701 ("US Maury Collection"), as has been reported in the past, appears to have pressures biased low (influencing early SLP patterns shown in Fig. 2b around 1850-60). No corrections for the US Maury SLP biases are known at present. However, Hendrik Wallbrink was studying these and other characteristics of the US Maury data in mid 2008, with a KNMI report anticipated in due course.
Proposed action:
None at this time (await KNMI report).


4-panel
Figure 1


Figure 2a. Bars show percentage frequency (left axis) of SLP values per deck (all ICOADS deck numbers are listed in Tables D6a-D6c). The line (right axis) indicates the total number of observations per deck during the period (note: log scale). Decks are ranked left to right from the lowest frequency to highest. Deck believed to contribute most heavily to anomaly changes: Deck 762 (Japanese Kobe Collection Data (keyed after decks 118-119)). Since total SLP values (not anomalies) are plotted here, anomalous patterns could result purely from geographic effects.


Figure 2b. Bars show percentage frequency (left axis) of SLP values per year. The line (right axis) indicates the total number of observations per year (note: log scale). Since total SLP values (not anomalies) are plotted here, anomalous patterns could result purely from geographic effects.

[Documentation and Software][Release 2.5 (Preliminary) Data Characteristics]


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Updated: May 11, 2016 19:12:23 UTC
http://icoads.noaa.gov/pre2.5slp.html