Steps Towards a Homogenized Sub-Monthly Temperature Monitoring Tool

Land surface air temperature products have been essential for monitoring the evolution of the climate system. Before a temperature dataset is included in such reports, it is important that non-climatic influences be removed or changed so the dataset is considered homogenous. These inhomogeneities include changes in station location, instrumentation and observing practices. Very few datasets are free of these influences and therefore require homogenization schemes. While many homogenized products exist on the monthly time scale, few daily products exist, due to the complication of removing break points that are truly inhomogeneous rather than solely by chance (for example, sharp changes due to synoptic conditions). Since there is a high demand for sub-monthly monitoring tools, there is a need to address these issues.

The Global Historical Climatology Network – Daily dataset provides a strong foundation of the Earth's climate on the daily scale, and is the official archive of daily data in the United States. While the dataset adheres to a strict set of quality assurance, no daily adjustments are applied. However, this dataset lays the groundwork for other products distributed at NCEI-Asheville, including the climate divisional dataset (nClimDiv), the North American monthly homogenized product (Northam) and the 1981-2010 Normals. Since these downstream products already provide homogenization and base period schemes, it makes sense to combine these datasets to provide a sub-monthly monitoring tool for the United States.

Using these datasets already in existence, monthly adjustments are applied to daily data, and then anomalies are created using a base climatology defined by the 1981-2010 Normals. Station data is then aggregated to the state level and then regions defined by the National Climate Assessment. Ranks are then created to provide informational monitoring tools that could be of use for public dissemination. This presentation goes over the product, including methodology, latest results, validation schemes, sources of uncertainty, and addressing future steps. It also provides an assessment of selected notable recent extreme events.