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HadISDH-marine is a global gridded monthly mean ocean surface humidity dataset. Hourly in situ dew point temperature and marine air temperature data from ships, moored buoys and ocean platforms are taken from ICOADS from 1973 to 2016. These are then converted to various humidity variables, quality controlled, bias adjusted and averaged over 5° by 5° degree gridboxes for each month. Monthly mean anomalies relative to the 1981-2010 climatology period are currently available. Actual values, climatology and climatological standard deviations will be available soon.
Gridded products are available for six humidity variables in addition to temperature - HadISDH-marine*.18.104.22.1686p:
LATEST VERSION: The current version of HadISDH-marine is 22.214.171.1246p and continues until December 2016. PLEASE NOTE THAT THIS IS A TEST PRODUCT AND HAS NOT YET PASSED THROUGH PEER REVIEW!!! Since 2011/2012 a distinct dry period is apparent (very clear in relative humidity) which is drier than in the similar in situ NOCSv2.0 product. This feature of HadISDH-marine may not be truly representative - a full investigation has not yet been completed. Please provide feedback on any issues and errors found to Kate Willett. Updates and full documentation will appear here in due course...
HadISDH-marine utilises simultaneous subdaily air temperature and dew point temperature data from ships, moored buoys and ocean platforms from ICOADS.3.0.0 and ICOADS.3.0.1 (Freeman et al., 2016) from January 1st 1973 to December 31st 2016. All humidity variables are calculated at hourly resolution.
Hourly humidity and temperature values are quality controlled to to remove gross random errors (bad locations, bad timings, climatological outliers, neighbourhood outliers).
Bias adjustments are also applied to the hourly data to account for increasing ship heights over time and changing proportions of poorly ventilated instruments.
The data are then averaged over 5° by 5° gridboxes centred on -177.5°W and -87.5°S to 177.5°E and 87.5°N for each month as anomalies and actual values. No interpolation is applied.
Data are available as monthly mean anomaly values relative to 1981 to 2010 climatology. Actual values, climatologies and a climatological standard deviation product will be available soon.
Uncertainty has been assessed at the observation level for measurement uncertainty, rounding uncertainty, height adjustment uncertainty and ventilation adjustment uncertainty. These will be made available at the gridbox monthly mean level at a later date along with spatio-temporal sampling uncertainty and coverage uncertainty.
Keep in touch
Follow us on twitter: @metofficeHadOBS for updates, news and announcements.
For more detailed information, follow our HadISDH blog. Here we describe bug fixes, routine updates and other exploratory analysis.
We have adapted our versioning system from CRUTEM4, and so the dataset numbering is of the form HadISDH.type.X.Y.Z.1234i. 'type' refers to the variable (e.g., landq=specific humidity). 'X' is for a major change and would be accompanied by a peer-reviewed paper or Met Office Technical Note. 'Y' is a more minor change, e.g., in one of the QC tests or homogenisation algorithms and would be described in a tech-note. 'Z' is a small change, for example addition or changes to data in the past. The last complete year of the dataset is given by '1234', and the final character shows if the dataset is f-final or p-preliminary. Therefore HadISDH.landq.126.96.36.1993p is the preliminary version of the dataset containing data up to the end of 2012.
The python code used was written by Kate Willett, John Kennedy and Robert Dunn. Some of it will be made available later here. We do not intend to provide in-depth support for this code. We do appreciate constructive feedback on this code.
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