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This paper examines the characteristics of the heatwave that affected western and central Europe in June 2017. Using a novel algorithm, we show that its extension, intensity, and persistence were comparable to those of other European mega‐heatwaves, but it occurred earlier in the summer. The most affected area was Iberia, which experienced devastating forest fires with human casualties and the warmest temperatures of the reanalysis period from daily to seasonal scales. The peak of the mega‐heatwave displayed an unprecedented warm air intrusion due to a record‐breaking subtropical ridge with signatures closer to those of July and August. The atmospheric circulation was the main triggering factor of the event. However, thermodynamical changes of the last decades made a substantial contribution to the event, by increasing the likelihood of surpassing high‐temperature thresholds. This episode could be a good example of a coming future, with high‐summer mega‐heatwaves occurring earlier., This work was supported by the Ministerio de Economía y Competitividad through the PALEOSTRAT (CGL2015‐69699‐R) and ISIPEDIA (ERA4CS) (PCIN‐2017‐046) projects. Ricardo M. Trigo and Pedro M. Sousa are supported by project IMDROFLOOD: Improving Drought and Flood Early Warning, Forecast and Mitigation using real‐time hydroclimatic indicators, JPND‐WaterJPI/0004/2014, financed by FCT/MCTES (PIDDAC). A. Sánchez‐Benítez was funded by grant FPU15/03958 from the Ministerio de Educación, Cultura y Deporte (MECD).

Ships' logbooks have been preserved in archives of different European countries. This paper reviews how their records provide reliable information relevant to meteorology and climatology, extending the observational record back to at least the early 18th century. This allows describing weather during historical events, improving the knowledge on hurricanes or unveiling multidecadal variability previously unsuspected, such as the steady enhancement of the Australian monsoon, the high variability of the atmospheric circulation over the Euro‐Atlantic region during the Late Maunder Minimum or the relationship between the Western North Pacific Summer Monsoon and the El Niño—Southern Oscillation. Observations from ships can feed long‐term reanalysis projects and contribute to reduce their uncertainties over the oceans. The extended record of observations also aids the search of analogues before the human fingerprint, thus improving the detection and attribution of climate change. The integration with paleoclimate proxies is a complex task that requires merging heterogeneous records with a wide range of time resolutions, spatial density, and responses to the climate system. However, recent international efforts open the field to new opportunities. Summing up, logbooks are a consistent, but underexploited, source of relevant climatic data that will widen our knowledge of the past climate. This in turn provides a way to better understand present climatic variations and predict future changes., This research was funded by the Spanish Ministerio de Economía y Competitividad through the projects CGL2013‐44530‐P, CGL2014‐51721‐REDT, CGL2015‐69699‐R, and CGL2015‐72164‐EXP/AEI.

This paper analyses for the first time the impact of high-latitude blocks and subtropical ridges on near-surface ozone (O3) in Europe during a 15-year period. For this purpose, a catalogue of blocks and ridges over the Euro–Atlantic region is used together with a gridded dataset of maximum daily 8h running average ozone (MDA8 O3) covering the period 1998–2012. The response of ozone to the location of blocks and ridges with centres in three longitudinal sectors (Atlantic, ATL, 30–0°W; European, EUR, 0–30°E; Russian, RUS, 30–60°E) is examined. The impact of blocks on ozone is regionally and seasonally dependent. In particular, blocks within the EUR sector yield positive ozone anomalies of ∼ 5–10ppb over large parts of central Europe in spring and northern Europe in summer. Over 20 and 30% of the days with blocks in that sector register exceedances of the 90th percentile of the seasonal ozone distribution at many European locations during spring and summer, respectively. The impacts of ridges during those seasons are subtle and more sensitive to their specific location, although they can trigger ozone anomalies above 10ppb in northern Italy and the surrounding countries in summer, eventually exceeding European air quality (AQ) targets. During winter, surface ozone in the north-west of Europe presents completely opposite responses to blocks and ridges. The anticyclonic circulation associated with winter EUR blocking, and to a lesser extent with ATL blocking, yields negative ozone anomalies between −5 and −10ppb over the UK, northern France and the Benelux. Conversely, the enhanced zonal flow around 50–60°N during the occurrence of ATL ridges favours the arrival of background air masses from the Atlantic and the ventilation of the boundary layer, producing positive ozone anomalies of ∼ 5ppb in an area spanning from the British Isles to the northern half of Germany. We also show that multiple linear models on the seasonal frequency of occurrence of these synoptic patterns can explain a considerable fraction of the interannual variability in some winter and summer ozone statistics (mean levels and number of exceedances of the 90th percentile) over some regions of western Europe. Thus, this work provides the first quantitative assessments of the remarkable but distinct impacts that the anticyclonic circulation and the diversion of the zonal flow associated with blocks and ridges exert on surface ozone in Europe. The findings reported here can be exploited in the future to evaluate the modelled responses of ozone to circulation changes within chemical transport models (CTMs) and chemistry–climate models (CCMs)., Carlos Ordóñez acknowledges funding from the Ramón y Cajal Programme of the Spanish Ministerio de Economía y Competitividad under grant RYC-2014-15036.