Subdaily meteorological measurements of temperature, direction of the movement of the clouds, and cloud cover in the Late Maunder Minimum by Louis Morin in Paris

We have digitized three meteorological variables (temperature, direction of the movement of the clouds, and cloud cover) from copies of Louis Morin’s original measurements (Source: Institute of History / Oeschger Centre for Climate Change Research, University of Bern) and subjected them to quality analysis to make these data available to the scientific community. Our available data cover the period 1665–1709 (temperature beginning in 1676). We compare the early instrumental temperature dataset with statistical methods and proxy data to validate the measurements in terms of inhomogeneities and claim that they are, apart from small inhomogeneities, reliable. The Late Maunder Minimum (LMM) is characterized by cold winters and autumns, and moderate springs and summers, with respect to the reference period of 1961–1990. Winter months show a significant lower frequency of westerly direction of movement of the clouds. This reduction of advection from the ocean leads to a cooling in Paris in winter. The influence of the advection becomes apparent when comparing the last decade of the 17th century (cold) and the first decade of the 18th century (warm). A lower frequency of westerly direction of movement of the clouds can also be seen in summer, but the influence is stronger in winter than in summer. Consequently, the unusually cold winters in the LMM can be attributed to a lower frequency of westerly direction of movement of the clouds. An impact analysis reveals that the winter of 1708/09 was a devastating one with respect of consecutive ice days, although other winters are more pronounced (e.g., the winters of 1676/77, 1678/79, 1683/84, 1692/93, 1694/95 and 1696/97) in terms of mean temperature, ice 15 days, cold days or consecutive cold days. An investigation of the cloud cover data revealed a high discrepancy in the seasons, where the winter season (DJF) (−13.2 %) and the spring season (MAM) (−12.6 %) show a negative anomaly of the total cloud cover (TCC), whereas summer (JJA) (−0.5 %) shows a moderate anomaly of TCC with respect to the 30 year mean of the Meteobluedata (1985–2014).

Analysis of Subdaily Meteorological Measurements by Louis Morin in the Late Maunder Minimum 1665 – 1709 in Paris

<p>Based on copies of the original data (source: Oeschger Center for Climate Change Research) we perform climate reconstructions for Paris between 1665 - 1709. The focus lies on the following meteorological variables: temperature, cloudiness, direction of movement of the clouds, precipitation and humidity. Apart from humidity, these meteorological variables were measured three times a day over the entire period from Louis Morin. Temperature and humidity were measured with instruments, whereas cloud cover, direction of movement of the clouds and precipitation were measured in a descriptive manner. In addition to the quantitative temperature measurements, conclusions about synoptic air movements over Europe are possible due to the additional meteorological variables. The Late Maunder Minimum is characterised by cold winters and moderate summers. Winter is characterised by a lower frequency of westerly direction of movement of the clouds. This reduction of advection from the ocean leads to cooling in Paris and also to less precipitation in winter. This can be seen very strongly between the last decade of the 17<sup>th</sup> century (cold) and the first decade of the 18<sup>th</sup> century (warm). A lower frequency of westerly direction of movement of the clouds can also be seen in summer, but the influence is stronger in winter than in summer. However, this reduction leads to moderate/warm temperatures in summer. So unusually cold winters in the Late Maunder Minimum can be attributed to a lower frequency of westerly direction of movement of the clouds.</p>

Analysis of Subdaily Meteorological Measurements by Louis Morin in the Late Maunder Minimum 1665 – 1713 in Paris

<p>Based on copies of the original data (source: Oeschger Center for Climate Change Research) we perform climate reconstructions for Paris. The focus lies on the following meteorological variables: temperature, cloudiness, moving direction of clouds and precipitation. We assess the early instrumental temperature dataset with state of the art statistical methods to get further knowledge of inhomogeneities. There are already several studies showing monthly and yearly means of the temperature, but a detailed statistical analysis based on the original measurements has not been done yet. Due to the lack of metadata, we do a qualitative analysis. With rare contemporary time series, like the CET (Central England Temperature), and proxydata, like grape harvest dates, we attempt to make a quantitative statement. We analyse and discuss the documentary datasets of the cloudiness and the moving direction of the clouds relating to the cooling in the Late Maunder Minimum. Because of the subjective character of documentary records, we compare these results with available data from former publications. Precipitation is given in terms of intensity and duration. We calculate indices like rainfall frequency and average rainfall per year/season/month.</p>

Euro-Atlantic Atmospheric Circulation during the Late Maunder Minimum

This paper presents observational evidence of the atmospheric circulation during the Late Maunder Minimum (LMM, 1685–1715) based on daily wind direction observations from ships in the English Channel. Four wind directional indices and 8-point wind roses are derived at monthly scales to characterize the LMM. The results indicate that the LMM was characterized by a pronounced meridional circulation and a marked reduction in the frequency of westerly days all year round, as compared to the present (1981–2010). The winter circulation contributed the most to the cold conditions. Nevertheless, findings indicate that the LMM in Europe was more heterogeneous than previously thought, displaying contrasting spatial patterns in both circulation and temperature, as well as large decadal variability. In particular, there was an increase of northerly winds favoring colder winters in the first half of the LMM, but enhanced southerlies contributing to milder conditions in the second half of the LMM. The analysis of the atmospheric circulation yields a new and complete classification of LMM winters. The temperature inferred from the atmospheric circulation confirms the majority of extremely cold winters well documented in the literature, while uncovering other less documented cold and mild winters. The results also suggest a nonstationarity of the North Atlantic Oscillation (NAO) pattern within the LMM, with extremely cold winters being driven by negative phases of a “high zonal” NAO pattern and “low zonal” NAO patterns dominating during moderately cold winters.

New insights into the reconstructed temperature in Portugal over the last 400 years

The consistency of an existing reconstructed annual (December–November) temperature series for the Lisbon region (Portugal) from 1600 onwards, based on a European-wide reconstruction, with (1) five local borehole temperature–depth profiles; (2) synthetic temperature–depth profiles, generated from both reconstructed temperatures and two regional paleoclimate simulations in Portugal; (3) instrumental data sources over the twentieth century; and (4) temperature indices from documentary sources during the late Maunder Minimum (1675–1715) is assessed. The low-frequency variability in the reconstructed temperature in Portugal is not entirely consistent with local borehole temperature–depth profiles and with the simulated response of temperature in two regional paleoclimate simulations driven by reconstructions of various climate forcings. Therefore, the existing reconstructed series is calibrated by adjusting its low-frequency variability to the simulations (first-stage adjustment). The annual reconstructed series is then calibrated in its location and scale parameters, using the instrumental series and a linear regression between them (second-stage adjustment). This calibrated series shows clear footprints of the Maunder and Dalton minima, commonly related to changes in solar activity and explosive volcanic eruptions, and a strong recent-past warming, commonly related to human-driven forcing. Lastly, it is also in overall agreement with annual temperature indices over the late Maunder Minimum in Portugal. The series resulting from this post-reconstruction adjustment can be of foremost relevance to improve the current understanding of the driving mechanisms of climate variability in Portugal.

New insights into the reconstructed temperature in Portugal over the last 400 years

The reliability of an existing reconstructed annual (December–November) temperature series for the Lisbon region (Portugal) from 1600 onwards is assessed in the present study. The consistency of this series with: (1) five local borehole temperature-depth profiles; (2) synthetic temperature-depth profiles generated from both reconstructed temperatures and paleoclimate simulations in Portugal; (3) instrumental data sources over the twentieth century; and (4) temperature indices from documentary sources during the late Maunder Minimum (1675–1715) is assessed. It is found that reconstructed annual mean temperature series in Portugal, after European-wide reconstructions, is not consistent with both borehole profiles and paleoclimate simulations in their long-term variability and trends. Hence, the non-linear trend in the paleoclimate simulations is estimated and added to the reconstructed series (first-stage calibration). The annual reconstructed series is then calibrated in its location and scale parameters, using the instrumental series and a linear regression between them (second-stage calibration). The resulting calibrated series is then in clear accordance with the low-frequency variability of both borehole temperature-depth profiles and paleoclimate simulations. This calibrated series shows clear footprints of the Maunder and Dalton minima, mainly attributed to changes in solar activity and explosive volcanic eruptions, and a strong recent-past warming, attributed to human-driven forcing. Lastly, it is also in overall agreement with independently-derived annual temperature indices for the late Maunder Minimum. Thus, the series resulting of this re-calibration process for Lisbon can be of foremost relevance to improve the current understanding of the driving mechanisms of climate variability in Portugal.