The performance of a new historical reanalysis, the NOAA–CIRES–DOE Twentieth Century Reanalysis version 3 (20CRv3), is evaluated via comparisons with other reanalyses and independent observations. ...This dataset provides global, 3-hourly estimates of the atmosphere from 1806 to 2015 by assimilating only surface pressure observations and prescribing sea surface temperature, sea ice concentration, and radiative forcings. Comparisons with independent observations, other reanalyses, and satellite products suggest that 20CRv3 can reliably produce atmospheric estimates on scales ranging from weather events to long-term climatic trends. Not only does 20CRv3 recreate a ‘‘best estimate’’ of the weather, including extreme events, it also provides an estimate of its confidence through the use of an ensemble. Surface pressure statistics suggest that these confidence estimates are reliable. Comparisons with independent upper-air observations in the Northern Hemisphere demonstrate that 20CRv3 has skill throughout the twentieth century. Upper-air fields from 20CRv3 in the late twentieth century and early twenty-first century correlate well with full-input reanalyses, and the correlation is predicted by the confidence fields from 20CRv3. The skill of analyzed 500-hPa geopotential heights from 20CRv3 for 1979–2015 is comparable to that of modern operational 3–4-day forecasts. Finally, 20CRv3 performs well on climate time scales. Long time series and multidecadal averages of mass, circulation, and precipitation fields agree well with modern reanalyses and station- and satellite-based products. 20CRv3 is also able to capture trends in tropospheric-layer temperatures that correlate well with independent products in the twentieth century, placing recent trends in a longer historical context.
ABSTRACT
We examine secular changes and multidecadal climate variability on a seasonal scale in northern France over the last 500 years and examine the extent to which they are driven by large‐scale ...atmospheric variability. Multiscale trend analysis and segmentation procedures show statistically significant increases of winter and spring precipitation amounts in Paris since the end of the 19th century. This changes the seasonal precipitation distribution from one with a pronounced summer peak at the end of the Little Ice Age to an almost uniform distribution in the 20th century. This switch is linked to an early warming trend in winter temperature. Changes in spring precipitation are also correlated with winter precipitation for time scales greater than 50 years, which suggests a seasonal persistence. Hydrological modelling results show similar rising trends in river flow for the Seine at Paris. However, such secular trends in the seasonal climatic conditions over northern France are substantially modulated by irregular multidecadal (50–80 years) fluctuations. Furthermore, since the end of the 19th century, we find an increasing variance in multidecadal hydroclimatic winter and spring, and this coincides with an increase in the multidecadal North Atlantic Oscillation (NAO) variability, suggesting a significant influence of large‐scale atmospheric circulation patterns. However, multidecadal NAO variability has decreased in summer. Using Empirical Orthogonal Function analysis, we detect multidecadal North Atlantic sea‐level pressure anomalies, which are significantly linked to the NAO during the Modern period. In particular, a south‐eastward (south‐westward) shift of the Icelandic Low (Azores High) drives substantial multidecadal changes in spring. Wetter springs are likely to be driven by potential changes in moisture advection from the Atlantic, in response to northward shifts of North Atlantic storm tracks over European regions, linked to periods of positive NAO. Similar, but smaller, changes in rainfall are observed in winter.
Observations are the foundation for understanding the climate system. Yet, currently available land meteorological data are highly fractured into various global, regional, and national holdings for ...different variables and time scales, from a variety of sources, and in a mixture of formats. Added to this, many data are still inaccessible for analysis and usage. To meet modern scientific and societal demands as well as emerging needs such as the provision of climate services, it is essential that we improve the management and curation of available land-based meteorological holdings. We need a comprehensive global set of data holdings, of known provenance, that is truly integrated both across essential climate variables (ECVs) and across time scales to meet the broad range of stakeholder needs. These holdings must be easily discoverable, made available in accessible formats, and backed up by multitiered user support. The present paper provides a high-level overview, based upon broad community input, of the steps that are required to bring about this integration. The significant challenge is to find a sustained means to realize this vision. This requires a long-term international program. The database that results will transform our collective ability to provide societally relevant research, analysis, and predictions in many weather and climate-related application areas across much of the globe.
The development of a daily historical European–North Atlantic mean sea level pressure dataset (EMSLP) for 1850–2003 on a 5° latitude by longitude grid is described. This product was produced using 86 ...continental and island stations distributed over the region 25°–70°N, 70°W–50°E blended with marine data from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS). The EMSLP fields for 1850–80 are based purely on the land station data and ship observations. From 1881, the blended land and marine fields are combined with already available daily Northern Hemisphere fields. Complete coverage is obtained by employing reduced space optimal interpolation. Squared correlations (r²) indicate that EMSLP generally captures 80%–90% of daily variability represented in an existing historical mean sea level pressure product and over 90% in modern 40-yr European Centre for Medium-Range Weather Forecasts Re-Analyses (ERA-40) over most of the region. A lack of sufficient observations over Greenland and the Middle East, however, has resulted in poorer reconstructions there. Error estimates, produced as part of the reconstruction technique, flag these as regions of low confidence. It is shown that the EMSLP daily fields and associated error estimates provide a unique opportunity to examine the circulation patterns associated with extreme events across the European–North Atlantic region, such as the 2003 heat wave, in the context of historical events.
The influence of zonal and meridional flow on surface temperature in the North Atlantic/European region is investigated. The degree to which the North Atlantic Oscillation (NAO) index reflects these ...two different flow types is considered, as is the relationship between the NAO index and surface temperature. Zonal and meridional circulation indices extending back to the early nineteenth or eighteenth centuries are based on surface pressure observations from the North Atlantic and Europe and on an empirical orthogonal function (EOF) analysis of European surface pressure from 1845-1995. The NAO index appears to integrate aspects of both zonal and meridional flow types. The pattern associated with the NAO index is composed of a quadrupole correlation pattern with surface temperature, showing positive correlations over Europe and the Sargasso Sea and negative correlations over northwest Africa and the Greenland/Labrador Sea region. Analysis indicates that the relationship between the NAO index and temperatures downstream of the Atlantic is associated with zonal flow, whereas the influence of the NAO on temperatures upstream is more closely linked to meridional flow patterns. Running correlations indicate that while there is no obvious link between the NAO index and the secular temperature trend, the second principal component of temperature is closely linked to atmospheric circulation, with a relationship which in winter has remained fairly steady through the twentieth century. Notwithstanding this, there have been changes in the strength of the correlation between temperature and circulation. These fluctuations in climate-circulation relationships should be further investigated and addressed in studies of climate change, especially in the calibration of paleoclimatic time series and downscaling models.PUBLICATION ABSTRACT
The quality of 51 series of surface pressure (extending back to between 1780 and 1871) over Europe is assessed using three different homogenization techniques. A new technique introduced here based ...on an iteration of multiple qualitative comparisons and adjustments (MCAs), and the Caussinus and Mestre technique, based on multiple decision rules and Bayesian statistics, are two methods that do not require a homogeneous reference series for the detection and adjustment of inhomogeneities. The third technique, the standard normal homogeneity test, does require a homogeneous reference series for the homogenization procedure, and has been used only on the last 100 yr of each station series. The results of the three methods, as well as the original, unadjusted data, are compared for differences in the variance of the individual series and in their interstation correlations. Empirical orthogonal function analysis is also used to assess differences in the results of the adjustment methods. The comparisons suggest that surface pressure in this geographical domain may be considered as being stationary over periods ranging from decades to centuries, and thus homogeneous parts of a surface pressure record can be used to adjust for inhomogeneities, as is done using MCA. It is also seen that EOF analysis can be an effective tool to assess the homogeneity of a dataset. The results of the EOF analysis show that inhomogeneities and poorly adjusted series can have undue influence on subsequent analyses.
A new NAO index is presented here using homogenized surface pressure data from Reykjavik and Gibraltar (for November to March) and Reykjavik and Ponta Delgada (for April to October). This index ...suggests that the positive trend in recent years is not unprecedented, as the early 20th century was also a period of persistently positive NAO values. The relationship between the secular warming trend and the influence of the NAO on near‐surface temperatures over the North Atlantic region and surrounding land masses is examined on a seasonal basis using standardized temperature anomalies since 1900. The near‐surface temperature field separates into two independent modes, which we designate a “warming” mode and dynamic (“NAO”) mode, with distinct seasonal cycles.
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