dataesr/scientific-paragraphs-categorization huggingface dataset:
The same methodology was used here for calibrating and validating MAIDEN at the nine records of PAGES2k2013. One site was found to be well calibrated and validated. The six sites for which MAIDEN calibration has successfully passed those tests will thus be incorporated into the DA procedure with MAIDEN. They can be seen on Fig. S2  (orange circles). In particular, there is no site in Tasmania. The iCESM1 data used in the DA framework are available at a monthly resolution. Yet, MAIDEN runs on a daily basis. To convert monthly data into daily data, we apply the same methodology to all the particles. We use a reference year of the daily GMF dataset (1950) which we modified to match the mean seasonal cycle over 1950-2000 CE, i. e. , a climatological seasonal cycle. Then, for a given particle, the monthly anomalies of the iCESM1 data relative to 1950-2000 CE are added (near-surface air temperature) or multiplied (precipitation) to the reference year of the daily GMF data.
Experiment design and diagnostics Different DA experiments are run in this study (Table  1 ), varying between them by (1) the records assimilated, (2) the tree-ring PSM included and its associated period of calibration, (3) the PSM error and (4) the period of the reconstruction. A first set of experiments is conducted over the 1900-2000 CE time period and compared with gridded climate datasets in order to evaluate the performance of our DA-based reconstructions regarding the use of statistical (TIC-reg) and process-based (TIC-MDN) dendroclimatic models separately, assimilating both ice core and tree-ring proxies. A second set of experiments is performed over the 1900-2000 CE time period to evaluate the contribution of tree-ring proxies in the data assimilation framework over the last century.
, 2020)  over the 1979-2000 CE time period, and against the GMF dataset (see Sect. 2. 4. 1 for more details on the dataset) over 1901-2000 CE, after linearly interpolating them on the iCESM1 grid (Sect. 2. 2). We focus on the near-surface air temperature, the cumulative precipitation and the 500-hPa geopotential height (ERA5 only). In addition to these variables, we also evaluate the Southern Annular Mode (SAM) over 1957-2000 CE. The SAM is the principal mode of atmospheric variability in the extratropics of the SH  (Marshall, 2003). It is associated with the north-south movement of the Westerlies and often defined as the difference between the normalized monthly zonal mean sea-level pressure at 40 • and 65 • S  (Gong and Wang, 1999; Marshall, 2003) , as chosen here. The SAM index from  Marshall (2003)  is used as a reference for our evaluation.
12 to 0. 60 for the correlation coefficients, and from -0. 12 to 0. 36 for the CE, for the four regions; Fig. 3 ; Table  3 ) in reconstructing the nearsurface air temperature when compared to the GMF climate dataset. Except in the South-Western Andes region (SAmSW in Table  3 ), the correlation coefficients and CE between reconstructed and GMF temperature are close for both experiments and particularly high in New Zealand (NZ). In Tasmania, no TRW records have been assimilated with MAIDEN, which may explain the lower CE (Table  3 ) for the TIC-MDN experiment, while the correlation coefficients are similar between both experiments. As for precipitation (Table  3  and Fig. 4 ), both TIC-MDN and TIC-reg are more skillful in the vicinity of the South American TRW proxies (SAmSW), with significant correlation coefficients of 0.
For precipitation (Fig. 9 ), the South-Western Andes is the region for which the ensemble spread is the smallest and the interannual variability the largest for both TIC-reg and TIC-MDN. Both experiments are also skillful for reconstructing precipitation in this region when compared with the state-of-the-art climate datasets over the last century (Table  3 ; Sect. 4. 1). The correlation coefficient between both reconstructions is 0. 58 and is statistically significant, so that the trend and timing of the reconstructions are close to each other. Both reconstructions display a very small trend before 1900 CE (a significant trend of -0. 586 and a non-significant trend of -0. 042 mm year -1 per decade for TIC-reg and TIC-MDN, respectively) and a negative trend after 1900 CE (a significant trend of -12.
g. atmospheric CO 2 concentration), having a comparable skill to a regression-based PSM is encouraging. There are still opportunities for improvement with the MAIDEN model while for the regression, the perspectives are more limited. For instance, we could improve the model-data comparison by using an observed tree growth index that is closer to the variable simulated by MAIDEN, i. e. , forest carbon accumulation, by combining density and ring width measurements. Different shortcomings related to the calibration of the MAIDEN model have also been addressed in  Rezsöhazy et al. (2020)  and  Rezsöhazy et al. (2021). If solved, this may likely help to increase the number of proxy sites where MAIDEN could be validated. It could also improve the performance of MAIDEN in simulating the relationship between climate and tree growth, and so enhance the skill of the DA-based reconstruction using MAIDEN as a PSM.
In particular, the calibration procedure could be more informative in the future, for instance in the definition of the prior ranges of the calibrated parameters, that could be set by species or biome. Different data sources, such as satellite data and the associated vegetation indexes, could also be used to better inform the different biological processes in the model (e. g. related to photosynthesis or phenology). Moreover, in this study, the criteria for including a TRW proxy record with the regression had to be less strict than for MAIDEN. MAIDEN was indeed validated at all the assimilated sites while the regression was not. This may provide a better stability of the MAIDEN model. It appears clearly that our DA framework does not include enough TRW proxy records in the mid-latitudes to properly reproduce the observed variance of near-surface air temperature and precipitation with both TRW PSMs, particularly at larger spatial scale (e.
As a consequence, the MAIDEN model simulates tree-ring growth series that are generally well correlated with the observations over the last 400 years, but which display a small variance compared to the observations. Despite this, at the regional scale, we have highlighted a difference between the two DA experiments in the reconstructed amplitude of the climate change in the preindustrial era relative to the 20th century. Using MAIDEN as a PSM for TRW records tends to reconstruct an average warmer and wetter climate than the regression-based PSM. This questions the almost exclusive use of linear statistical PSMs for tree-ring proxies in data assimilation to reconstruct the past climate changes. However, this would need an in-depth investigation with more TRW proxy records in order to be confirmed, as well as additional analysis to ensure the validity and robustness of MAIDEN and its calibration in our framework, and more generally of sophisticated tree-growth PSMs.
For now, our framework only offers a limited skill of the reconstructions, and we are far from providing a complete hemispheric reconstruction of atmospheric fields in the Southern Hemisphere. However, our results are encouraging for MAIDEN, and more generally for the use of dendroclimatic process-based models in DA. In the future, mechanistic models like MAIDEN will likely become an important tool of the DA framework that would help overcome the potential bias associated with regression models. However, this would require to continue to improve those models, including their calibration, so that they could be applied more efficiently and more skillfully at large spatial scale. Calibrating a model like MAIDEN at large spatial scale remains a challenge, and incorporating it into a data assimilation procedure is still more technically time consuming than the traditional statistical approach.
Acknowledgements. JR was F. R. S-FNRS research fellow, Belgium (grant no. 1. A841. 18); QD is F. R. S-FNRS postdoctoral researcher, Belgium; HG is research director at F. R. S. -FNRS, Belgium; JG is emeritus research director at CNRS, France. This research has been supported by the Belgian Research Action through Interdisciplinary Networks (BRAIN. be) from the Belgian Science Policy Office in the framework of the "East Antarctic surface mass balance in the Anthropocene: observations and multiscale modelling (Mass2Ant)" project (contract no. BR/165/A2/Mass2Ant). Computational resources have been provided by the supercomputing facilities of the Université catholique de Louvain (CISM/UCL) and the Consortium des Équipements de Calcul Intensif en Fédération Wallonie Bruxelles (CÉCI) funded by the Fond de la Recherche Scientifique de Belgique (F.
Here, we provide ice phenology records and their corresponding meta-data for 78 lakes from 12 countries in North America, Europe, and Asia. These lakes comprise some of the longest ice phenology records collected around the Northern Hemisphere (>100 years) and also include lakes from countries such as Canada, Iceland, Norway, and Poland, that have typically not been included in global synthesis studies or within the National Snow and Ice Data Centre (NSIDC) Lake and River Ice Phenology Dataset (LIAG  20  ). In this study, in addition to the ice phenological records, we asked: i) What are the physical characteristics of the lakes?; ii) What were the definitions of ice-on and ice-off?; iii) How were ice observations made and recorded?; iv) Why was the ice record started historically?; and vi) Did the methodology change over the entire time series?.
Ice phenology records were collected solely via visual observations. Observers would stand on the municipality of Barrie shoreline at the west end of Kempenfelt Bay and look due east for ice coverage information to identify when the west end of Kempenfelt Bay was completely frozen in the winter or ice-free in the spring. Remote sensing images from the Moderate Resolution Imaging Spectroradiometer (MODIS) were recently incorporated to supplement two recent missing years in the spring of 2004 and fall of 2017. There is a limited uncertainty because of subjectivity of observers, inconsistent numbers of observers and observing locations during the data collecting period, and possible historical errors associated with the early start of the dataset in 1852. Maine, United States. Ice-out data for New England, including Maine, New Hampshire, and Massachusetts, were compiled and reported by Hodgkins and James  21  then updated in Hodgkins  22.
A secondary observer recorded Fig. 1  Lakes with ice phenology data described in this dataset are outlined and filled in blue, using HydroLAKES polygons (Messager et al. 44  ). A blue highlight is added to better identify the locations of even the smallest lakes. Insets show detail of the northeastern U. S. and Swiss lakes' positions. dates for 1959, 1962-68, 1970-78, and 1997-98; for these years, ice-off dates were adjusted by the average difference in the dates between the primary and secondary observers  21. Kezar Lake's earliest ice phenology record is 1901 by Arthur P. Stone (1901-1961) and kept at the Lovell town office. There are no missing years in the time series. According to the current observers, John Bacchiochi and Stan Tupaj, who have been conducting observations for about the past two decades, ice-off date is defined as the date when navigation is possible from one end to the other end of the lake.
Ice cover is observed daily from the summit (where the observatory is located 145 m above the pond) with the assistance of binoculars if necessary. When the pond is not visible from the summit, observations are made at the shoreline. The pond is considered thawed when a trace amount (five percent or less) of ice remains after the last full freeze. Ice-on is also recorded at this site as the first date with complete ice coverage; intermittent ice coverage is tracked by the observers. Michigan, United States. Grand Traverse Bay in Lake Michigan ice record started in 1850 which along with Bayfield Bay in Lake Superior  15  is the longest ice phenology dataset for the Great Lakes. The ice-on date is recorded when the lake is covered with ice over West Bay from the southern shore to Power Island  25.
Ken Stewart, University of Buffalo. The diaries were kept from 1839 by consecutive owners of the Lorenzo Mansion (members of the Ledyard family) and are kept at the library of the Lorenzo Mansion State Historical Site. Data after 2008 are from Mr. Phillip Hart, Cazenovia, and his father before him, kept track of these dates for some time and is the source of Ken Stewart's earlier data. The original Ken Stewart dates were maintained when there was a discrepancy between records from the Hart family and Stewart's assessment. Mr. Hart states that he checks the ice by driving around the lake and that he does not count ice-on dates if the lake broke up again the same day (i. e. , lake skimmed over with ice for a short time). Over the course of the time-series, changes in data collection procedures were documented in the database.
Recently, data were supplemented with a 24/7 live feed from a webcam observing the main portion of the lake from the south looking north. When ice-on or ice-off dates near, the lake is further observed in person. Since the historical definition of ice-on and ice-off data have not been well documented, there may be an uncertainty corresponding to the time needed for ice-off to occur. Over the time series, there are no missing years in the ice-off dataset, but 11 years are missing from the ice-on record. The first observation of ice was recorded from Mohonk Lake in 1932. Both ice-on and ice-off dates have been collected since 1932-present. The Smiley Family began recording weather data in 1896 and Daniel Smiley began recording lake ice phenology dates in 1932 each year until his passing in 1989.
Note that these problematic data were used by Magnuson et al. 4  , but corrected in subsequent papers from that group e. g. 28. Data obtained from 1901 to 1974 were from seven different observers and were kept at the Oneida Fish Culture Station. After 1975, CBFS personnel have been observing ice conditions in the middle of the lake (Shackelton Point) due East, West, and North in both the mornings and afternoons. Further, the amount of open water is noted. For Oneida Lake, ice-on dates are more difficult to define as the ice usually temporarily forms and breaks up again before the final freeze over. This dataset follows the convention of the National Ice Database which states that the first date that the lake completely froze over is recorded as the ice-on date. Ice-off date is better defined as ice often leaves the lake in a few days.
When notes indicate the presence of short ice-on periods prior to the given first ice-on date, a three-day ice duration is added to those periods when calculating ice duration for that winter. Otsego Lake's ice phenology record begins in 1849. Ice thickness data exists for the winters of 1970-71 to 1974-75. The dataset is currently maintained by the SUNY Oneonta Biological Field Station. Records from 1843-1972 were kept by a series of Weather Observers, beginning with George Pomeroy Keese (1843-1910), followed by Elizabeth Cooper Keese (1910-1930), and then staff of a local newspaper the Freeman's Journal (1930-1972). Those data were compiled and described in a 1973 Climatological Summary  29. Definitions of ice-on and ice-off were described for 1843-1930: ice-on date was recorded when the lake was "entirely closed by ice", ice-off date recorded when "the last ice left the lake".
Observations are sometimes made multiple times a day with the first observation at around 8 am if the conditions are appropriate. It is easier to detect open water if there is light snowfall. Ice-on date is recorded as the date the lake has been frozen for two days. However, waterfowl will often keep water open, so up to about five acres of open water full of waterfowl is acceptable for the lake to be categorized as frozen. The ice-off date is defined as when the lake is free of ice other than small ice plates that float around or are washed up on the leeward shore of the lake. Freeze/thaw events within a winter are additionally recorded in the database. Factors such as variation in observation point, weather, and ability to see last ice formation contribute to uncertainty in the recent data.
Sometimes, the exact time is given in the paper reports by the observer, but these are not available in the database since only dates could be stored in the database. All other notes written by reporters were also kept on paper but not digitized. Remote sensing observations from MODIS and Sentinel-2 and web cameras supplement more recent observational data. However, they are not regularly used for screening because of cloudiness and the fact that many of these Finnish lakes are too small and fragmented for remote sensing. Ice data collection procedure instructions, including the different freezing and melting stages, have been written and published in Hydrological Yearbooks (1910-2010). There may have been unremarkable changes in the procedure, although there have been no changes since the 1960s according to the definitions in the yearbooks.
88588° N; 10. 14479° E) towards the south. Different staff of the NVE have been following the same procedure to collect this data. However, since the 1980s, the same observer has recorded the ice dates. In recent years, web-cameras and residents who live near the lake provide additional information to increase the data accuracy during critical periods. The ice-on date is recorded as when some ice first appears on the lake, whereas the ice-off date is when the lake is completely ice free. The dataset additionally contained information of daily weather conditions and water level. Lake Aursunden's ice phenology record began in 1902 by the regional hydropower company (Glommens og Laagens Brukseierforening). Between 1902-2012, the data were collected through weekly morning observations from the western shore of the lake (62.
68067° N, 11. 46401° E) towards the east. As the observers lived nearby, sometimes additional information was obtained in between the weekly visits particularly during critical periods of ice formation and thaw. After 2002, remote sensing including Moderate Resolution Imaging Spectroradiometer (MODIS) from the National Aeronautics and Space Administration (NASA) (up to 2015) and Sentinel-2 from the European Space Agency (ESA) (2015 onward) have been additionally used to collect ice phenology data to increase the accuracy. The ice-on date is defined when the ice is first observed, whereas the ice-off date is the date there is no ice on the lake. The regional hydropower company (Glommens og Laagens Brukseierforening) started the lake ice phenology dataset for Lake Tesse in 1908 with weekly observations in the morning from the northern shore (61.
80535° N; 8. 94799° E) while looking southward. The ice-on date is the day when some lake ice appears for the first time and ice-off is recorded as the date that the lake is completely ice free. Lake Tunhovdfjorden's record began in 1920 by the NVE to provide information for the development of a hydropower reservoir. Weekly direct observations were made in the morning from the southern shore (60. 32223° N; 8. 92416° E) towards the south of the lake from 1920 to 1994. There was a large gap in the ice record during 1994-2014 after which the ice data were collected using remote sensing observations from Sentinel-2 at the lake centre (60. 42573° N; 8. 83726° E). The observers that lived near the lake sometimes provided additional information between weekly visits which increased the data accuracy during critical periods.
The ice-on date is the day when some lake ice first appears, whereas the ice-off date is when the lake is completely free of ice. For all of the Norwegian lakes described in this study, additional features of the ice were recorded prior to and during the time of observation including: first ice in registration site, partial freeze-up at registration site, complete freeze-up at registration site, first ice near shore, ice freeze-up near shore, partial freeze and break up if there was open water in sight of several kilometers, breaks in data record, freeze-up across the entire lake, and ice-free across the entire lake. Poland. Serwy Lake's ice phenology record began in 1888. The Russian Ministry of Road Information started the record to manage inland waterways and reported it annually from 1888 to 1918.
Sweden. Lakes Orsasjön, Näckten, Kallsjön, Storuman, Göuta, Runn, and Jukkasjärvi are lakes located across Sweden. The systematic recording of lake ice began in the late 19th century and early 20th century, for example in 1859 for Runn, in 1870 for Orsasjön, Kallsjön and Göuta, and in 1908 for Näckten. For all of these lakes, ice-on dates are defined as the day when the main lake area is first covered by ice and the ice cover lasts for at least 3 days over at least two-thirds of the lake area. Ice-off date is defined as when the main lake area is ice free implying that some small bays may still have ice cover. If the lake freezes again, the last date when it opens is taken as the ice-off date  38. Freeze-thaw events throughout the winter season are also recorded. The Swedish Meteorological Institute (SHMI) was founded in 1945 and started recording lake ice data for national monitoring using a Standard Operating Program established in the national ice monitoring program.
The institute also collected older ice observations and homogenized them. They further used visual observations (including daily observations for larger lakes) as the primary means to collect data which were supplemented with satellite imagery in the last few years. Although the procedure for collecting data was consistently used throughout the study and the SHMI's staff was highly experienced, there may be limited uncertainty associated with the variability in personal judgements and observations. Switzerland. Ice coverage information from ten lakes located on the Swiss plateau, an area in Switzerland with altitudes between 400-700 m, is included in the database. As the average winter air temperatures in this area of Switzerland are slightly above the freezing point, these relatively deep lakes no longer freeze each winter.
For these lakes, a common definition was used for ice-on and ice-off dates. The ice-on date is defined when the lake is completely or almost completely (>90%) covered with ice for more than one day. On the other hand, the ice-off date is defined as the date when more than 10% of the lake has open water (this implies that less than 90% of the lake is still frozen). In years when the historical information is from newspapers, there may be uncertainty in the dataset of a few days. It is possible that freezing events were not reported by newspapers, and would be missed. We believe that this risk is in general small, as the freezing of larger lakes did not occur each winter, and had economical (e. g. , fishery), and socio-cultural (e. g, ice skating) implications. Visual observations might be especially affected in case of impaired visibility (e.
After 1901, information was collected via newspapers (specifically Luzerner Zeitung) up to 1955. Family Hofer, in addition to fishermen on Lake Baldegg and Lake Sempach continued the record based on visual observations up to recently. Ice is observed on the lake at various locations visually. Lake Biel's ice record was started by the fishermen Arnold Martin, out of his curiosity and for fishing purposes in 1923. From 1923 to 2006, ice phenology information was observed and systematically recorded each year into the family's diary. Arnold Martin and family would observe the lake mostly in the morning in the southern direction from the shore or on boats while on the lake. Measurements of ice depth and percent ice coverage were also noted. Since 2007, data have been obtained unsystematically from newspapers with additional information provided by webcams.