1) How does the new version compare?
v4.5.1.2022f is virtually identical to v4.4.0.2021f over the 1973-2021 period for specific humidity (q) and relative humidity (RH). Each year there is usually a small change to the source station dataset as a few stations or subperiods of stations are added or lost from processing within the source dataset (NOAA NCEI's ISD). A bug fix also resulted in a few additional stations compared to last year's version. In terms of gridboxes with sufficient presence over the climatology period the new version v4.5.1.2022f actually results in 9 lost gridboxes and 13 (for q) and 11 (for RH) additional gridboxed (Figs. 1 and 2 panel a). but clearly these have made negligible difference to the regional mean timeseries.
The overall story of increasing specific humidity is concurrent in both versions with no change to long-term trends in v4.5.1.2022f that have an extra year of data other than the moistening in the tropics being 0.01 g kg -1 decade -1 smaller than for v4.4.0.2021f. (Figure 1 panels d to g). Across the globe (Figure 1 panel a) the vast majority of gridboxes show trends in the same direction (95% of gridboxes - Figure 1 panel b), with 85.6% of these both showing increasing q (Figure 1 panel b). Trends in opposite directions occur in 4.5 % of gridboxes and are mostly in the Southern Hemisphere, across South America and northern Australia.
The overall story of decreasing relative humidity (except over the tropics) is also still valid in both versions, with long-term negative RH trends in v4.5.1.2022f being -0.01 to -0.04 %rh decade -1 more negative than in v4.4.0.2021f (Figure 2 panels d to g). Across the globe (Figure 2 panel a), 87% of gridboxes have trends in the same direction in both versions which is a slightly smaller proportion compared to q (Figure 1 panel b). Overall, 58% of gridboxes agree on negative trends and 30% agree on positive RH trends.
2) What's New?
We use HadISD.3.3.0.2022f as the basis for HadISDH.land.v4.5.1.2022f which represents no technical changes from HadISD.3.2.0.2021f relevant to HadISDH other than an additional 12 months of data and any ISD level processing changes during the previous 12 months. These occasionally lead to removal or addition of a few stations or sub-periods of stations. In this case, and in addition to the bug fix noted below, this resulted in an almost 300 more stations initially but this reduced to only ~50 after HadISDH processing.
A second change is the formula for calculating wet bulb temperature from dewpoint temperature and air temperature. Errors were found when the air temperature was very high but dewpoint temperature very low, resulting in spuriously high wet bulb temperatures. The Stull (2011) formula is now used as this has a far wider range of applicability. See the blogpost for details.
This mostly affects the wet bulb temperature fields although differences are very small, and far less than 1 degree for the most part. Differences are larger over warm, dry air conditions. The calculated wet bulb temperature is used to decide whether to calculate vapour pressure with respect to ice or water and so this new formula can lead to very small changes in vapour pressure and variables that use vapour pressure in their calculation (specific humidity and relative humidity). Stull (2011) tends to give higher wet bulb temperatures overall which will result in fewer uses of the calculations with respect to ice and therefore fractionally higher vapour pressures and related values. As it is consistently used across the time period it should not impact long-term trends in anomalies.
A third change was a minor bug fix which prevented a few stations from completion of the HadISDH processing suite if they were removed by a completeness test relevant to the new HadISDH.extremes product (coming soon). This product is processed simultaneously with HadISDH.land. Correcting this resulted in 36 extra stations passing through to the final dataset but 9 stations being lost. The lost stations are removed during homogenisation. The new stations will have influenced the network of correlating neighbours which in turn increases the power of the homogenisation to detect and adjust/remove inhomogenious periods. Stations with periods removed may no longer pass the temporal completeness checks and so are removed.
3) Summary of changes by level of technicality.
MAJOR CHANGES (X):
- none
MINOR CHANGES (Y):
- Change of wet bulb temperature formula to Stull (2011) - see blogpost.
BUG FIXES AND HISTORICAL DATA UPDATES (Z):
- 9555 compared to 9278 initial selection stations last year
- use of HadISD.3.3.0.2022f as the basis which includes retrospective improvements (to correct data, add or remove data sections) to the historical data in NCEI's ISD archive are ongoing. These are not documented.
- bug fix to permit 36 new stations to pass through to the final dataset that were being removed when failing the new HadISDH.extremes completeness checks (product coming soon).
- the above bug fix resulted in 9 existing stations being removed during the homogenisation process.
4) Station Counts
| Version | Initial Stations | Selected Stations | Final Stations |
Final Stations RH |
|---|---|---|---|---|
| v4.5.1.2022f | 9555 | 5641 | 5396 | 5445 |
| v4.4.0.2021f | 9278 | 5581 | 5347 | 5393 |
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