ICOADS Web information page (Wednesday, 11-May-2016 19:09:54 UTC):

Release 2.5 (Preliminary) Data Characteristics

1. Introduction

This webpage provides temporal and spatial comparisons between preliminary Release 2.5 and Release 2.4 data for 1662-1969, links to additional webpages exploring in detail noteworthy homogeneity questions in the preliminary data, and plots illustrating duplicate elimination (dupelim) performance and quality control results (note: characteristics of final 1662-1969 Release 2.5 data are described on this webpage).

Figure 1. The time periods of major new or improved data sources being blended into Release 2.5 are spanned by horizontal green lines. Each dataset name is appended with the date range and approximate number of reports. The solid blue curve is the number of Release 2.4 reports; the solid red curve is the number of preliminary Release 2.5 reports through 1969.

2. Release 2.5 (preliminary) 4-panel plots

Figures 2a1 through 2i6 provide 4-panel comparison plots between preliminary Release 2.5 data and Release 2.4 data (2° enhanced monthly summaries in both cases) for 20-year periods (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 humidity plots are omitted for the earliest three periods due to general data sparsity.

2° ENH 1850-1869 1870-1889 1890-1909 1910-1929 1930-1949 1950-1969
Sea Surface Temperature Figure 2a1 Figure 2a2 Figure 2a3 Figure 2a4 Figure 2a5 Figure 2a6
Air Temperature Figure 2b1 Figure 2b2 Figure 2b3 Figure 2b4 Figure 2b5 Figure 2b6
Scalar Wind Figure 2c1 Figure 2c2 Figure 2c3 Figure 2c4 Figure 2c5 Figure 2c6
U Wind Component Figure 2d1 Figure 2d2 Figure 2d3 Figure 2d4 Figure 2d5 Figure 2d6
V Wind Component Figure 2e1 Figure 2e2 Figure 2e3 Figure 2e4 Figure 2e5 Figure 2e6
Sea Level Pressure Figure 2f1 Figure 2f2 Figure 2f3 Figure 2f4 Figure 2f5 Figure 2f6
Total Cloudiness Figure 2g1 Figure 2g2 Figure 2g3 Figure 2g4 Figure 2g5 Figure 2g6
Specific Humidity       Figure 2h4 Figure 2h5 Figure 2h6
Relative Humidity       Figure 2i4 Figure 2i5 Figure 2i6


3. Release 2.5 (preliminary) map comparisons

Figure 3. Decadal (1880-89) totals of sea level pressure (SLP) observations (upper) illustrating data additions between Releases 1, 2.0, and preliminary 2.5 data. The colors show the number of observations in a 2° box per decade. Grey indicates 1-10; red indicates 11-100; orange indicates 101-400; yellow indicates 401 or more. (Middle and Lower) As for (upper) except for sea surface temperature (SST) and relative humidity (RHUM). Note: More map comparison figures are planned for addition at a later date, to document coverage changes in final Release 2.5 data.

Figures 3e1 through 3g3 show decadal differences (preliminary Release 2.5 minus Release 2.4) of numbers of reports. The matrix of plots is organized by columns for each century, versus rows for each decade within the centuries. No data were added to Release 2.5 for the 1700s through 1730s, and the amounts of data added back to 1662 were very small, so plots for those decades have been omitted (note: Release 2.4 data began in 1784).

  1700s 1800s 1900s
00s   Figure 3a2 Figure 3a3
10s   Figure 3b2 Figure 3b3
20s   Figure 3c2 Figure 3c3
30s   Figure 3d2 Figure 3d3
40s Figure 3e1 Figure 3e2 Figure 3e3
50s Figure 3f1 Figure 3f2 Figure 3f3
60s Figure 3g1 Figure 3g2 Figure 3g3
70s Figure 3h1 Figure 3h2  
80s Figure 3i1 Figure 3i2  
90s Figure 3j1 Figure 3j2  


4. Release 2.5 (preliminary) data continuity questions

The following three webpages explore some noteworthy data-difference patterns (between preliminary Release 2.5 data and Release 2.4 data) for three variables:
Sea surface temperature (SST)
Sea level pressure (SLP)
Wind speed (W)
5. Release 2.5 (preliminary) dupelim results


Figure 4a. Numbers of reports added to, or deleted from, the output preliminary Release 2.5 data during dupelim, separately by deck, covering 1792-1877. The deck 156 reports deleted around 1860, without corresponding additions from other decks, were previously undetected duplicates (i.e., they matched other reports already in ICOADS).


Figure 4b. As for Figure 4a, but covering 1878-1949.


Figure 4c. As for Figure 4a, but covering 1950-69.


Figure 5. The larger plot shows total numbers of reports output in the preliminary Release 2.5 data, stratified by deck, for 1830-1969 (Tables D6a-D6c). The smaller plot shows patterns for the period prior to 1830, which is almost exclusively composed of data from decks 730 (CLIWOC) and 701 (US Maury).

6. Release 2.5 (preliminary) quality control results

In Figures 7a through 7f, bars show the percentage frequency (left axis) of observation (a1) trimming flag value. Specifically, where a1 is the individual observation under scrutiny, g is the smoothed median, and s1 and s5 are the smoothed lower and upper median deviation:
E = data unusable (SF, AF, and PF, only)
C = limits missing (ocean/coastal box)
7 = greater than 4.5 sigma upper limit (a1 > g + 4.5*s5)
6 = less than 4.5 sigma lower limit (a1 < g - 4.5*s1)
5 = greater than 3.5 sigma upper limit (g + 3.5*s5 < a1 <= g + 4.5*s5)
4 = less than 3.5 sigma lower limit (g - 4.5*s1 <= a1 < g - 3.5*s1)
3 = greater than 2.8 sigma upper limit (g + 2.8*s5 < a1 <= g + 3.5*s5)
2 = less than 2.8 sigma lower limit (g - 3.5*s1 <= a1 < g - 2.8*s1)
1 = within 2.8 sigma limits (g - 2.8*s1 <= a1 <= g + 2.8*s5)
The line (right axis) indicates the total number of extant observations per deck during the period (note: log scale). Landlocked 2° boxes (LZ=1) were removed in a final Release 2.5 IMMA processing step (Figure 6), or during processing of earlier ICOADS Releases (for previously available data sources). Decks containing no extant data for a given variable were not plotted (e.g., deck 736 "Byrd Antarctic Expedition" includes only SLP). As an important modification to the trimming procedure for Release 2.5, the 1910-49 trimming limits for RH were used for flagging all RH data within the 1662-1909 period. This approach was used because the original 1854-1909 trimming limits for RH generally were missing (see Figs. 1-4 on this webpage, which also reveal smaller gaps in the earlier trimming limits for other variables including SLP and SST). In Fig. 7a, more than 20% of the SST observations for deck 246 (Antarctic Expeditions) were flagged E as unusable; this unexplained problem was resolved in the final Release 2.5 data (compare Fig. 7a there) by reacquiring the data from the UK.

sea surf. temp. (SF)air temp. (AF)u comp. wind (UF)v comp. wind (VF)sea level press. (PF)rel. hum. (RF)
Figure 7a Figure 7b Figure 7c Figure 7d Figure 7e Figure 7f

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