1
Supporting Material
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Impact of volcanic stratospheric aerosols on diurnal temperature range (DTR) in
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Europe over the past 200 years: observations versus model simulations
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5
Renate Auchmann1, Florian Arfeuille1, Martin Wegmann1, Jörg Franke1,
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Mariano Barriendos2, Marc Prohom3, Arturo Sanchez-Lorenzo4,5, Jonas Bhend6,
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Martin Wild4, Doris Folini4, Petr Štěpánek7, and Stefan Brönnimann1
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9
1
Institute of Geography and Oeschger Centre for Climate Change Research,
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University of Bern, Switzerland
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2
Department of Modern History, University of Barcelona, Barcelona, Spain
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3
Catalan Meteorological Service (SMC, Meteocat), Barcelona, Spain
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4
Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
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5
Department of Physics, University of Girona, Girona, Spain
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6
CSIRO Marine and Atmospheric Research, Aspendale, Australia
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7
Global Change Research Centre AS CR, v.v.i., Brno, Czech Republic
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Corresponding author: R. Auchmann, Institute of Geography and Oeschger Centre for
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Climate
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(renate.auchmann@giub.unibe.ch)
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Change
Research,
University
of
Bern,
Switzerland.
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1. Details on station information and homogeneity of records
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25
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Geneva
Continuous observations in Geneva began in the late 18th century. During the
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first period of observations, temperature measurements were performed twice daily
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(once at sunrise and again at 14:00 LT), approximating the daily minimum (Tn) and
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maximum (Tx) temperatures, respectively [Auchmann et al., 2012]. Only occasionally
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were sunset measurements also performed. Within the DigiHom project [Füllemann et
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al., 2011], all sub-daily observations and measurements from Geneva during the
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period 1799–1863 were digitized. Internally homogeneous temperature data are
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available in the period 1799-1821; Auchmann et al. [2012] corrected the temperature
34
data for an artificial trend and standardized the units. During this period, the station
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was located in the old botanical garden. The same mercury thermometer was used and
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placed in the shadow of a stake (Bibl. Brit. Vol. 1).
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Tx and Tn are available from 1863 to present (MeteoSwiss, IDAWEB). Since
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1863, the station (at that time located at the Observatoire de Genève) has undergone
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several changes; in April 1959 the station was relocated to the airport (Genève-
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Cointrin), around 5 km northwest of the city and a new thermometer screen was
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installed. Until 1966 measurements continued in parallel at the Observatoire de
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Genève. The relocation and instrumentation change caused inhomogeneities in the
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series [Z'graggen, 2006]. However, this is outside of our reference periods. In 1980,
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the English screen was exchanged by a ventilated thermometer, which did not cause
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significant inhomogeneities [Z'graggen, 2006; Kuglitsch et al., 2012].
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Kuglitsch et al. (2012) compiled all documented changes in the Tx/Tn series
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from metadata and station history records and compared them to the results of three
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break detection algorithms. We use this information to determine the homogeneous
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reference periods.
50
Cloud cover observations had been performed twice daily from the very
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beginning. Until 1863, heterogeneous descriptions (sometimes very detailed) were
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noted. The original descriptions in the period 1799–1821 have been classified into six
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categories [Auchmann et al., 2012]. However, the cloud cover series seems to only be
54
homogeneous from around 1812 onwards. In the period from 1874 to present, cloud
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cover observations have been performed thrice daily and given in octas. Overall, the
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change in cloud cover categories may lead to inhomogeneities during the study
57
period, which is accounted for when determining homogeneous sub-periods. We use
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the 7:00 and the 12:00 observations to determine sky conditions at the time of Tx and
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Tn, respectively. The year 1900 is almost completely missing. In the period 1962–65,
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around 25% of only the noon series is missing (i.e., mainly weekend observations).
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This might be a consequence of the relocation to the airport, a possible change in
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observation practices, or variable observers. In this period, we only use the morning
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sky observation to determine a clear day.
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65
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Basel
Continuous observations in Basel began in the mid-18th century [Bider et al.,
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1958]. From 1876 onwards, daily Tn and Tx were measured and are used use in this
68
study. From 1885 to 1897, there is a gap in the series. The station experienced a major
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relocation in 1929 from the Bernoullianum to Basel-Binningen, which caused an
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inhomogeneity in the series [Z'graggen, 2006]. In 1966, the Wild screen was replaced
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by a Stevenson screen [Auchmann and Brönnimann, 2012], introducing an additional
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inhomogeneity to the series. To account for this inhomogeneity, we set the base
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period for the Agung eruption (other stations 1960–90) to 1935–65 (Table S2). From
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1978 onwards, a ventilated thermometer was used, introducing another
75
inhomogeneity, which we considered when determining the base periods (Table S2).
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Thrice daily cloud cover observations are digitally available from 1864
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onwards and are given in nine categories (octas). Since 1981, ten cloud cover
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categories are used (i.e., with the tenth category representing foggy conditions).
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Again, the change in categories may lead to inhomogeneities, which are accounted for
80
when determining the homogeneous sub-periods. Nothing is known about changes in
81
observers, which might be a further reason for inhomogeneities. A visual inspection
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of the series homogeneity reveals a possible change in the frequency distribution in
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1929 (i.e., coincident with the relocation of the station).
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85
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Prague
The station Prague-Klementinum started continuous meteorological
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measurements in 1775. Prague-Klementinum is located in the Old Town of Prague in
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the College of St. Clement. Hence, the station has always been urban [Brázdil and
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Budiková, 1999]. In the beginning of the series, temperature was measured near the
90
window of a second-story flatin a metal screen attached to a north-facing wall (11 m
91
above ground) in a closed courtyard [Brázdil and Budiková, 1999]. From 1775 to
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1889, the thermometer has shifted several times between the second and first floors.
93
Since then, the thermometer has been permanently installed on the first floor [Brázdil
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and Budiková, 1999]. Also some “structural changes in the courtyard” [Brázdil and
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Budiková, 1999] were reported in 1863, 1924, and 1929. According to Hlaváč [1937]
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[Brázdil and Budiková, 1999] none of those changes caused inhomogeneities in the
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series. However, as an urban site, urban heating effects have biased the temperatures
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series [Brázdil and Dobrovolný, 1993; Brázdil and Budiková, 1999] . Because we
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consider anomalies in contemporary (short) reference periods, this is assumed to be
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irrelevant. We use the Tn and Tx series, which represent minimum and maximum
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temperatures for a period of 24 hours, from 21 to 21 UTC+1 (ECA&D).
102
Cloud cover observations have also been performed from the beginning of the
103
series. However, the data has not been analyzed or used for any studies so far (email
104
communication, Nemec, L., 2011). Cloud cover is given in tenths throughout the
105
period. Missing values only occur in 1870, 1903 (ca. 25 values), 1939 (ca. 4 months),
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and during a longer period (1961–91) during which no morning cloud cover
107
observations are available. For the latter, we selected clear-sky days based only on the
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noon cloud cover observations. Nothing is known about the changes in observers,
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which may lead to inhomogeneities in the series. We visually inspected the temporal
110
homogeneity of the cloud cover series and found the period 1840 to1843 very likely
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to be inhomogeneous. Another noticeable period starts around 1897 and ends (for the
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morning series) around 1919, when more fully covered days were observed. However,
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the transition is gradual and there is no clear evidence of an inhomogeneity. We
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determine the reference periods accordingly, for instance, for Krakatau (Table S2).
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116
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Barcelona
Meteorological observations in Barcelona started in 1780 [Trigo et al., 2009],
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but little is known about instruments and observational techniques [Rodríguez et al.,
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2001]. Three observations are taken per day (i.e., at 7:00, 12:00, and 22:00).
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However, nothing is known about the exactness of observation times. In our study, we
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use the 7:00 and 12:00 temperature series, assuming that the morning series
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approximate daily minimum temperatures and that the noon series are close to the
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daily maximum temperatures. It has been reported that, at least during the first period,
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observations were taken outside and on a north-facing wall [Trigo et al., 2009]. In
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1885, the first official observations were made [Rodríguez et al., 2001; Trigo et al.,
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2009]. At the moment, data for the early period are only available in digital format
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from1780 to 1825. Several efforts are made to complete both the temperature and
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cloud cover sub-daily series following the study proposed in Prohom et al. [2012].
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These and should be available shortly.
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Throughout the 19th century many changes are reported making the Barcelona
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series discontinuous [Trigo et al., 2009]. For this early period, cloud cover
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observations are reported in three categories: clear, presence of clouds (different
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density), and total sky coverage . However, the data had not yet been explored. We
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inspected the cloud cover series visually and found the early series to be
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homogeneous.
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Tx and Tn series are available from 1924 onwards (ECA&D). However, there
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is a gap starting on December 1, 1927 and lasting until 1943. Measurements after
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1943 were taken at the airport [Rodríguez et al., 2001].
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For the period 1961–2011, cloud cover is only available as a daily mean
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(calculated as the mean of the 7:00, 13:00, and 18:00 observations) and is given in
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nine categories. Nothing is known about the changes in observers, which may lead to
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inhomogeneities in the series. A visual homogeneity inspection did not reveal any
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notable breaks in the series.
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Hohenpeissenberg
Hohenpeissenberg is situated in Bavaria, southern Germany, in the northern
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pre-Alps. Meteorological measurements and observations at Hohenpeissenberg started
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in 1781 (at that time a monastery). Hence, Hohenpeissenberg is one of the oldest
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mountain observatories in Europe and worldwide. Many of the records are available
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without discontinuities since the beginning of the measurements [Winkler, 2009]. In
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contrast to many other European stations the location of the station did not change
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over time (i.e., no large station relocations were undertaken). The station of
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Hohenpeissenberg is located on a mountain (Hoher Peissenberg; 985 m a.s.l.), which
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offers several advantages. First, the environment around the station has not changed
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considerably over the past 200 years. Relative to stations located within city centers or
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suburbs, the temperature series of the isolated Hohenpeissenberg are independent of
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urban heating effects [Mitchell, 1953; Winkler, 2009]. Second, due to the location on
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a stand-alone mountain, daily variability is damped compared to surrounding stations
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in the valley, which are heavily influenced by ground-level cold air during the
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nighttime [Winkler, 2009].
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162
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Thrice daily measurements have been taken since 1781. However, Tn and Tx
measurements and cloud cover observations have been continuously taken since 1879.
Auer et al. (2007) homogenized monthly mean temperature series for the
‘Greater Alpine Region’ including Hohenpeissenberg. We compared the
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homogenized monthly series to monthly averages calculated from our data (with daily
166
mean = (Tx+Tn)/2) and show the difference series (homogenized minus our raw data)
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in Figure S1. We use metadata from Hohenpeissenberg together with Figure S1 to
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define homogeneous sub-periods as reference periods.
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Cloud cover is observed thrice daily (at 6:00, 12:00, and 18:00 UTC)
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throughout the period 1879–2009 and given in nine categories (octas). Times are
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given in UTC throughout the paper unless otherwise noted. Comprehensive metadata
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and information on the station history, instruments, data quality, and observers are
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available for Hohenpeissenberg. A detailed compilation and summary of the available
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material and sources was performed by the DWD and Winkler [2009, and references
175
therein]. Large changes at Hohenpeissenberg that could have affected the Tx and Tn
176
series or the cloud cover observations are listed in Table S1.
177
We visually inspect the homogeneity of the cloud cover series, which reveals
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an overall general change in the distribution of the cloud cover frequencies around the
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mid- to end of the 1930s. A change in general measurement techniques and
180
responsibilities on December 1, 1936 [Winkler, 2009; see Table S1] may be the
181
reason for this change in the frequency distribution. From 1879 to 1936, 12 different
182
official observers (usually priests or vicars) were in charge. However, usually the
183
measurements were read and observations were also done by helpers (e.g., teachers or
184
the cook of the parish; see Table S1). From 1937 to 1940, five technical employees of
185
the “Reichswetterdienst” made the observations (DWD station history). From 1940
186
until now, employees of the mountain station have been in charge of the observations.
187
Also in 1940, a small relocation of the station was undertaken, including a vertical
188
shift of 10m (DWD station history), which could have affected the Tx and Tn series.
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In addition, a change in the extreme thermometers was reported around 1937. In 1971,
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electronic data processing equipment was installed.
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192
2. Base and reference periods
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194
195
References
Auchmann, R. and S. Brönnimann (2012), A physics-based correction model
196
for homogenizing sub-daily temperature series, J. Geophys. Res., 117(D17), D17119,
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doi:10.1029/2012JD018067.
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Auchmann, R., S. Brönnimann, L. Breda, M. Bühler, R. Spadin, and A.
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Stickler (2012), Extreme climate, not extreme weather: the summer of 1816 in
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Geneva, Switzerland, Clim. Past, 8(1), 325–335, doi:10.5194/cp-8-325-2012.
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M., Nanni, T, Maugeri, M., Mercalli, L., Mestre, O., Moisselin, J.-M., Begert, M.,
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Müller-Westermeier, G., Kveton, V., Bochnicek, O., Stastny, P., Lapin, M., Szalai, S.,
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Szentimrey, T., Cegnar, T., Dolinar, M., Gajic-Capka, M., Zaninovic, K., Majstorovic,
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Z., and E. Nieplova (2007), HISTALP – Historical instrumental climatological
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surface time series of the greater Alpine region 1760-2003, Int. J. Climatol., 27, 17-46,
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doi: 10.1002/joc.1377.
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Bider, M., M. Schüepp, and H. Rudloff (1958), Die Reduktion der 200jährigen
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Basler Temperaturreihe. Archiv für Meteorologie, Geophysik und Bioklimatologie,
211
Serie B, 9(3–4): 360–412, LA – German, doi:10.1007/BF02243047.
212
Brázdil, R. and M. Budiková (1999), An urban bias in air temperature
213
fluctuations at the Klementinum, Prague, The Czech Republic, Atmospheric
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Environment, 33 (24–25), 4211–4217.
215
Brázdil, R. and P. Dobrovolný (1993), The utilization of long temperature
216
series for studying climatic fluctuations in central Europe, Zeszyty Naukowe
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Uniwersytetu Jagiellonskiego, Prace Geogr., 95, 151–162.
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Fischer, E. M., J. Luterbacher, E. Zorita, S. F. B. Tett, C. Casty, and H.
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Wanner (2007), European climate response to tropical volcanic eruptions over the last
220
half millennium, Geophys. Res. Lett., 34(5), L05707, doi:10.1029/2006GL027992.
221
Füllemann, C., M. Begert, M. Croci-Maspoli, and S. Brönnimann (2011),
222
Digitalisieren und Homogenisieren von historischen Klimadaten des Swiss NBCN
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Resultate aus DigiHom, Technical report, Arbeitsber. MeteoSwiss, Zürich,
224
Switzerland.
225
Hlaváč, V. (1937), Temperature Patterns of the Capital of Prague, Praha, 95.
226
Kuglitsch, F. G., R. Auchmann, R. Bleisch, S. Brönnimann, O. Martius, and
227
M. Stewart (2012), Break detection of annual Swiss temperature series, J. Geophys.
228
Res., 117, D13105, doi:10.1029/2012JD017729.
229
230
Mitchell, J. (1953), On the causes of instrumentally observed secular
temperature trends, J. Met., 10, 244–261.
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232
Pfister, C. (1999), Wetternachhersage - 500 Jahre Klimavariationen und
Naturkatastrophen (1496–1995), Bern: Paul Haupt.
233
Prohom, M., Barriendos, M., Aguilar, E. and Ripoll, R. (2012), Recuperación
234
y análisis de la serie de temperatura diaria de Barcelona, 1780-2011. Cambio
235
climático. Extremos e impactos. Publicaciones de la Asociación Española de
236
Climatología (AEC), Serie A, nº 8. Salamanca, ISBN: 978-84-695-4331-3, pp. 207–
237
217.
238
Rodríguez, R., M. Barriendos, P. D. Jones, J. Martín-Vide, and J. C. Peña
239
(2001), Long pressure series for Barcelona (Spain), Daily reconstruction and monthly
240
homogenization, Int. J. Climatol., 21(13), 1693-1704, doi:10.1002/joc.696.
241
242
Trigo, R. M., J. M. Vaquero, M.-J. a. Alcoforado, M. Barriendos, J. a. Taborda,
R. García-Herrera, and J. Luterbacher (2009), Iberia in 1816, the year without a
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summer, Int. J. Climatol., 29(1), 99–115, doi:10.1002/joc.1693.
244
Winkler, P. (2009), Wissenschaftshistorische Untersuchungen zur Geschichte
245
und insbesondere zur Datenqualität der langen meteorologischen Reihen des
246
Observatoriums Hohenpeissenberg, Berichte des Deutschen Wetterdienstes, 233(1),
247
187 pp, doi:10.1007/s00704-009-0108-y.
248
Z'graggen, L. (2006), Die Maximaltemperaturen im Hitzesommer 2003 und
249
Vergleich zu früheren Extremtemperaturen, Arbeitsberichte der MeteoSchweiz, 212,
250
74 pp.
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252
253
254
255
256
257
258
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Table S1. Large changes at the site Hohenpeissenberg.
Date
Type of change
Change
1936
Measurement technique
1.12.1936
1937
1940
Official competence
Instrument
Observer
1971
Measurement technique
Window screen (outside window on
northern wall of house on second floor)
replaced by free-standing shelter screen
“Reichswetterdienst”
Change in the extreme thermometers
Employees of the mountain station were
in charge of the observations
Electronic data processing equipment
was installed
Possibly
affected
Tx and Tn
Cloud cover
Tx and Tn
Cloud cover
Tx and Tn
260
261
262
263
264
265
266
267
268
269
Table S2. Base periods (length of reference periods in parentheses) provided in years.
Krakatau
1883
1874–
99
(23)
1871–
96
(23)
1879–
1901
(20)
Santa
Maria
1902
1890–
1920
(25)
1897–
1919
(17)
1890–
1920
(25)
1800–21
(16)
—
—
—
1961–90
(24)
—
1876–
1920
(25)
1876–
1920
(25)
1898–
1927
(25)
1938–65
(25)
Unknown
Tambora
1809
1815
GE
—
1812–21
(7)
PR
1799–
1825
(21)
1799–
1825
(21)
HP
—
—
BC
1800–21
(16)
BS
—
Katmai
Agung
1912
1897–
1927
(26)
1897–
1919
(17)
1897–
1927
(26)
1963
1939–65
(24)
1961–91
(25)
1960–90
(25)
El
Chichón
1982
1970–
2000
(25)
1970–
2000
(25)
Pinatubo
1991
1980–
2010
(25)
1980–
2010
(25)
1971–99
(23)
1971–99
(23)
1970–
2000
(25)
1980–
2010
(25)
1970–
2000
(25)
1980–
2010
(25)
285
Figure S1: Difference series of homogenized monthly temperature series from
286
Hohenpeissenberg from the HISTALP (Historical Instrumental Climatological
287
Surface Time Series of the Greater Alpine Region) project by Auer et al. (2007)
288
minus raw monthly mean temperatures calculated from the data used in this study.
T diff [histalp - study] (°C)
-4
-3
-2
-1
0
1
2
1879/1
1880/1
1881/1
1882/1
1883/1
1884/1
1885/1
1886/1
1887/1
1888/1
1889/1
1890/1
1891/1
1892/1
1893/1
1894/1
1895/1
1896/1
1897/1
1898/1
1899/1
1900/1
1901/1
1902/1
1903/1
1904/1
1905/1
1906/1
1907/1
1908/1
1909/1
1910/1
1911/1
1912/1
1913/1
1914/1
1915/1
1916/1
1917/1
1918/1
1919/1
1920/1
1921/1
1922/1
1923/1
1924/1
1925/1
1926/1
1927/1
1928/1
1929/1
1930/1
1931/1
1932/1
1933/1
1934/1
1935/1
1936/1
1937/1
1938/1
1939/1
1940/1
1941/1
1942/1
1943/1
1944/1
1945/1
1946/1
1947/1
1948/1
1949/1
1950/1
1951/1
1952/1
1953/1
1954/1
1955/1
1956/1
1957/1
1958/1
1959/1
1960/1
1961/1
1962/1
1963/1
1964/1
1965/1
1966/1
1967/1
1968/1
1969/1
1970/1
1971/1
1972/1
1973/1
1974/1
1975/1
1976/1
1977/1
1978/1
1979/1
1980/1
1981/1
1982/1
1983/1
1984/1
1985/1
1986/1
1987/1
1988/1
1989/1
1990/1
1991/1
1992/1
1993/1
1994/1
1995/1
1996/1
1997/1
1998/1
1999/1
284
283
282
281
280
279
278
277
276
275
274
273
272
271
270