1st question: 

The two top pictures show auroral lights over the frozen river Kitinen. The black horizontal belt under the auroral lights near the middle of the frame is the tree line on the opposite bank of the river.

2nd question:

In Finland, two full-scale manned magnetic observatories were set up temporarily for the polar years 1932–1933. They were Petsamo (69.5°N; 31.2°E) near the coast of the Arctic Sea, now in the territory of Russia, and Kajaani in East-Finland (64.2°N; 27.7°E) (Simojoki, 1978).

3rd question:

About 200 photographs of aurora rescued from the destruction of the Sodankylä observatory in 1944 and recently found in the library of the Finnish Meteorological Institute are now in the data archive of the SGO.

RC3 comment: "However, some more useful information can be added for such purpose.  For example, the date of photographed nights of about 100 copies that we rescued recently should be given".AC reply: The dates of rescued auroral photographs 1927–1929 will be given in Appendix A (see below).

RC3 line 42-48:  The following replaces the sentence on line 42 "Trials ...".Trials of height measurements and photography of auroras were made at the Sodankylä Polar year observatory 1882–1884. Photographs of auroras were unsuccessful because the sensitivity of the films available was too low for exposing faint auroral lights. The results of simultaneous visual triangular height measurements of auroras were unrealistic and scattering widely because the baseline was too short (4 kilometres) for accurate determinations of auroral forms observed at both ends of the baseline.

RC3  line 46: "This technique". Reply: The aurora is photographed simultaneously from two or more stations situating at mutual distances of several tens of kilometres. The sites are connected by telephone, so that the observers can direct their cameras towards the same region of sky and expose at the same time. The location of stars on the photographs fixes the astronomical orientation of auroral forms (Chapman and Bartels, 1940; Störmer, 1955).

RC3 line 58: Ok capital letters will be used as suggested.

RC3 line 64-68: The number of staff is mentioned here in order to point out that very few workers operated the observatory working on many demanding tasks.

RC3 line 78: Changed: "As planned by Störmer"

RC3 line 89: The word "special" is removed

RC3 line 113: No reference is found but in the annual report of the SGO in 1928 there is a mention that in the lack of a photo projector, the height determinations could not be done in the SGO. This was the reason to send the auroral photographs to Norway in Störmer's laboratory for analysis by an image projector. However, no information exists about the possible results.

RC3 line 118: "How many nights are taken in total during 1927-1929 and how many are rescued?" The number of rescued photographs is 226 out of total amount 592. A list of dates will be given in the appendix.

RC3 line 122: As was mentioned above the sensitivity of film used in auroral cameras during the Polar Year station Sodankylä 1883-83 was too low for successful photographing.

RC3 line153: Ok. I will write "discrete aurora over the zenith (so called corona)"

RC3 line 157: "magnetic K-index increased up to 8/9" is now "the three-hour magnetic K-index increased up to 8/9". K = 8 corresponds to magnetic field amplitudes between 990 nT and 1500 nT, and when K = 9, amplitudes are  > 1500 nT

RC3 Figure 6. Each of six frames in one plate was exposed one after the other in about 30 seconds intervals. The whole photographing operation in this case took a few minutes.

RC3 205: The two temporary observatories during the Polar Year 1932-1933 were Petsamo (69.5°N; 31.2°E) near the coast of the Arctic Sea, now in the territory of Russia, and Kajaani in East-Finland (64.2°N; 27.7°E).

RC3 line 212: The symbols introduced by Sucksdorff exist in hand-written paper document only. They were used in connection with visual observations mainly during the Polar Year programme 1932–1933 in Lapland. I think that these symbols are not relevant for the present manuscript in which auroral photography is the main theme. A study of the visual auroral observations based on Sucksdorff's auroral codes could be a goal for a future investigation.

RC3 line 214-216:  All visual observations carried out in 1932–1940 by Sucksorff's team are without photographing, naked eye sightings only. The original material, consisting of about 750 observations, is in the archive of the SGO.In the annual reports of the SGO, compiled by Sucksdorff, there are written, "very few auroral photos were taken" in the years after 1929. However, no further information exists about these "few photographs".

RC3 line 224-225: Calculations of auroral heights were done in the Störmer's auroral laboratory in Oslo. However, no information exists about the results obtained.For the figure caption for Fig. 4: The lower edge of the auroral form is about 20 degrees above the horizon towards the brightest stars of the constellation Pegasus.

RC3 line 240: The following sentence is added: All data requests should be directed to the SGO (eija.tanskanen@sgo.fi). The data plotted in Fig. 8 will be in the Appendix B (see below).

RC3 line 254-255: The following sentence will be added after the end of line 257: This long-term trend in the annual auroral occurrence rate may be connected with the centennial Gleissberg cycle of solar activity (e.g., Feynman and Ruzmaikin, 2014).

Appendix A

______________________________________

Table 1. Dates of available auroral photographs

at the SGO 1927–1929

______________________________________

Date                  Number of single photos

1927

Nov 18                          24

Nov 19                           6

Dec 13                           33

Dec 14                            3

Dec 18                            6

Dec 28                           42

1928

Jan 27                           46

Mar 11                          18

Mar 13                          30

1929

Feb 27                           18

Total                             226

______________________________________

Appendix B

________________________________________________

Table 2. Annual numbers of auroral nights¹

at the SGO 1914–1954, local magnetic activity index² (Ak),

and sunspot number³ (R)

________________________________________________

Year      Number of nights             Ak                    R

1914                 43                     24                     16.1

1915                 73                     52                     79.0

1916                 75                     68                     95.0

1917                 68                     64                     173.6

1918                 26                     88                     134.6

1919                 27                     83                     105.7

1920                 18                     57                     62.7

1921                 24                     51                     43.5

1922                 16                     66                     23.7

1923                 10                     26                     9.7

1924                   8                    26                     27.9

1925                 16                     42                     74.0

1926                 29                     76                     106.5

1927                 21                     58                     114.7

1928                 25                     64                     129.7

1929                 43                     71                     108.2

1930                 48                     119                   59.4

1931                 32                     59                     35.1

1932                 43                     76                     18.6

1933                 45                     63                     9.2

1934                 32                     45                     14.6

1935                 24                     57                     60.2

1936                 52                     63                     132.8

1937                 52                     75                     190.6

1938                 39                     96                     182.6

1939                 52                     98                     148.0

1940                 59                     97                     113.0

1941                 85                     108                   79.2

1942                 51                     100                   50.8

1943                 65                     115                   27.1

1944                 36                     66                     16.1

1945                 33                                             55.3

1946                 57                     70                     154.3

1947                 63                     106                   214.7

1948                 72                     100                   193.0

1949                 64                     99                     190.7

1950                 37                     113                   118.9

1951                 82                     136                   98.3

1952                 52                     142                   45.0

1953                 80                     105                   20.1

1954                 52                     70                     6.6

________________________________________________

¹ Finnish Meteorological Institute - meteorological yearbooks

² Sodankylä Geophysical Observatory - magnetic yearbooks

³ Solar Influences Data Analysis Center WDC-SILSO

RC4: "The description of data recovery needs more details. What is the ultimate source of information on the number of those (about 400) photographs that are not found? Maybe some observatory or personal notebooks of E. Sucksdorff (ES)."

Reply: The main sources of information about the history of auroral images taken at SGO are hand-written notebooks of Eyvind Sucksdorff for 1927–1929. There are described relevant data for each photograph (date, exposure time, orientation of camera etc.). In Appendix A there is a table showing the dates of rescued auroral photos as well as the lost ones (see below) based on Sucksdorff's notebooks.

RC4: "These source documents should all be described, scanned and made publicly available in digital format. Even better if they were read to digital tables. Now nothing of such possible development is mentioned. Similarly, the photographs should be scanned and stored in a public digital archive."

Reply: The original source information is stored in tables and auroral images available have been digitized. They are in the digital archive of the SGO. However, for the moment our policy of releasing the auroral data is restricted to individual requests only which should address to the SGO (eija.tanskanen@sgo.fi).

RC4: " How does the image timing go? Judging from the temporal time evolution of auroral forms and intensity depicted in the 6 images, a likely order is clockwise from top left to end at middle left."

Reply: The image order in the plate of six single photographs was clockwise.

RC4: "As described in the manuscript, there was a vigorous photography program in Norway, which led to the improved determination of auroral height. In this situation, I was left wondering why at all Norwegians wanted to install a station in SGO? Historical order of events is missing. "

Reply: There was a plan promoted by the scientific community in Norway that the auroral photography network will be expanded outside Norway for the coming Polar Year 1932–1933. Stations in Greenland, North-Norway (Tromsö) and on Bear Island in the Arctic Sea were set up. The SGO observatory was located far away in the east from the sites of the Norwegian auroral program and could allow a more wide observation view for the auroral photography during the Polar Year.

Eyvind Sucksdorff visited Störmer's auroral laboratory in 1938 and discussed there about auroral research but no common writings exist.

RC4: "Have SGO photographic films been saved and archived in Norway?"

Reply: According to Sucksdorff's notebooks there are comments that images from Sodankylä and from the auxiliary station were sent to Oslo for further analysis. I have been in contact to Oslo University and asked if they have auroral images from the SGO but without results.

RC4: "Visual auroral observations by ES from 1932 to 1944 are said to be archived at SGO. What does it practically mean? "

All observations with related information (observer, time, location, coding, weather info etc.) must be made publicly available with related URLs included. Similarly for the "routine" observations from 1914 until 1954. What about the auroral observations by the Danes? Are these included in the same dataset?"

Reply: Results of visual auroral observations 1932–1944 carried out at the SGO and several sites in Lapland are in hand-written notebooks only. We have plans to transcribe the results in form of tables and make summaries of the observations. There are about 10 rather unorganized notebooks available including the visual observations carried out by the Danish team.

RC4: " Line 29. Contribution by ES was pioneering probably only in Finland."

Reply: This is rewritten: In Finland, Eyvind Sucksdorff´s contribution to research of auroras was a pioneering effort with minimal resources.

RC4: " Lines 83 and 89. Is frame = photograph? If yes, ignore "frame". Does 600 photographs mean 100 plates?

Reply: Yes, "frame" is changed to "photograph". Yes, c. 600 photographs mean c. 100 plates.

RC4: " Line 94. 200 photographs means about 35 paper sheets? How many exactly?

Reply: The paper copies of single photographs are larger than the originals in a plate. The size of a single paper photograph is about 4 x 4 cm. Each paper sheet consists of 10 single photographs. The number of sheets is 20.

RC4: " Statement (see lines 149-151) "The second greatest magnetic storm during this cycle, as recorded by magnetometers at Sodankylä.” "The second greatest magnetic disturbance." would be a possible statement once authors define exactly, how the intensity estimate was made, perhaps based on the local K index? "

Reply: The lines 149-151 are rewritten as follows: The February 27, 1929 magnetic storm observed at the SGO and other magnetic stations at high latitudes was one of the major magnetic storms during the solar cycle 16 (1923–1933) (e.g., Goldie, 1929; Rowland, 1929).

RC4: " Also, additional evidence on storm evolution is needed to verify if the disturbance of the previous night was part of the same storms. Surely it was not "a minor storm".

Reply: Corrected: The February 27, 1929 magnetic storm at the SGO started already in the evening hours of February 26 and ended near midday of 28th (Fig. 5).

RC4: " Fig. 6 caption would read more clearly as follows: "The two top pictures show auroral lights reflected from the frozen river Kitinen. The black belt under the auroral lights, which is the tree line on the other side of the river, is seen in all pictures, most clearly in the top row." This is the setting in all 6 photographs. The exact start and end times (hh:min:sec) of each photograph should be added to the left or right of each panel so that a rough estimate of auroral intensity and temporal order could be obtained. If these images were obtained at 30s intervals, the total time is at most 3.5 min, not 5 min as in text. "

Reply. The caption is rewritten as follows:

            Figure 6. Auroral displays on February 27, 1929 as captured by a camera at           the Sodankylä observatory. Each frame on the photographic plate represents       auroras in intervals of about 30 seconds at about 20 h (UT) to the west. The          exposure time varies between 1 to 30 seconds. The first photograph is on the   top left.

            The two top pictures show auroral lights reflected from the frozen river     Kitinen. The black belt under the auroral lights, which is the tree line on the       other side of the river, is seen in all pictures, most clearly in the top row.

            Next four pictures show rapidly changing auroral forms, veils and spirals. Two      bright spots are planets Jupiter (upper) and Venus (lower) in the west and          about 15° from the horizon.   (Photo: E. Sucksdorff¨s collection SGO).

The total time (about 5 min) is corrected: about 3.5 minutes.

RC4: " The exact start and end times (hh:min:sec) of each photograph should be added to the left or right of each panel so that a rough estimate of auroral intensity and temporal order could be obtained. "

Reply:  They will be given later. There are some problems with Sucksdorff's time writings during the storm.

RC4: " Figure 8. While the number of auroral nights gives some information about the occurrence of auroras, the more correct way is to present the fraction of the nights with auroras to the number of all nights that were "available" for auroras to be observed. So, in addition to the figure of absolute numbers, authors should present these fractions. Otherwise, the study is rather futile. As seen in the figure, there are times when auroral occurrence and magnetic activity are very different, even differently located over the cycle. Also, the multi-decadal rise is dubiously large in auroras. These differences are, very likely, due to the variable weather conditions, which would be corrected by the above fractions."

Reply: We have added new data to the auroral data shown in Fig. 8 (see below) The data is taken from the compilation of visual auroral data by Legrand and Simon (1987). The data collection comprises of several thousands auroral records from sub-auroral latitudes in the northern hemisphere from the years 1780–1979This data series correlates reasonable well with the time variation of auroras obtained form the SGO during 1914–1954. However, there are certain anomalies in the SGO curve when magnetic activity and auroral occurrence are quite different due probably varying weather and cloudy conditions. The original conclusion that there has been an increasing trend in the occurrence of aurora 1914-1954 at SGO is still valid.

[Legrand, J.-P.  and Simon, P.A., 1987. Two hundred years of auroral activity (1780–1979). Annales Geohysicae, 5, 161–167].

There is a picture attached in the end of the reply sheet showing the correlation between global aa-index and auroral occurrence number derived by Legrand & Simon. The linear correlation for the years 1914–1954 is +0.79.

RC4: "Mention in text and in caption what is the magnetic activity index used here."

Reply: The magnetic activity index is the annual mean of daily Ak number taken from the magnetic yearbooks of the SGO.

RC4 line 205. "Line 205. Mention which observatories."

Reply: The two temporary observatories during the Polar Year 1932-1933 were Petsamo (69.5°N; 31.2°E) near the coast of the Arctic Sea, now in the territory of Russia, and Kajaani in East-Finland (64.2°N; 27.7°E).

RC4: " Line 241-242. This is an odd sentence. Auroral occurrence studies are also part of auroral studies."

Reply: This sentence is now: Independent from auroral studies, Visual observations of the occurrence of auroras were made in connection with daily meteorological observations at the Sodankylä observatory since the founding of the observatory in 1914.

RC4: " Line 156. Ref to Fig. 5 must be earlier in text.

Reply: Corrected

RC4: " Line 254. It is multi-decadal, not decadal."

Reply. Ok. Corrected.

RC4: " Line 272. Write: auroras obtained almost one hundred years ago are the first ones in Finland."

Reply: Ok. Corrected

RC4: " References are relevant except for all the three papers by Tanskanen. Neither Tanskanen et al., 2005, nor Tanskanen, 2009, deals with auroral observations. "

Reply: Tanskanen et al. (2005) and Tanskanen (2009) found that the largest substorm numbers and peak amplitudes were found during the declining solar cycle phases. Their analysis was derived using magnetic data from the solar cycle 1993–2003. This similar to conclusion here that auroral occurrence rate is generally enhanced during the declining phase of a solar cycle.

RC4: "  Tanskanen, 2022, is not even a scientific paper. "

Reply: Ok. This reference is deleted.

RC4: " The centennial increase in geomagnetic activity was found by Mayaud in 1972".

Reply: Yes. The reference Mayad (1972) is added in the reference list.

Mayaud, P.N.: The aa Indices: A 100-Year series characterizing the magnetic activity. Journal of Geophysical Research, 77, 6870–6874, https://doi.org/10.1029/JA077i034p06870, 1972.

Appendix A

_________________________________

Table 1a. Dates¹ of available auroral photographs

at the SGO 1927–1929

________________________________________

Date                  Number of single photos

1927

Nov 18                          24

Nov 19                           6

Dec 13                           33

Dec 14                            3

Dec 18                            6

Dec 28                           42

1928

Jan 27                           46

Mar 11                          18

Mar 13                          30

1929

Feb 27                           18

Total                             226

______________________________________

Table 1b. Dates¹ of photographs lost

in the war 1944

______________________________________

Date                  Number of single photos

1928

Dec 6                              9

1929

Jan 29                           18

Feb 17                           11

Feb 27                           147

Mar 7                            12

Mar 8                            40

Mar 11                          42

Mar 14                          78

Mar 27                          27

Total                             384

_____________________________________

¹ The data is based on original hand-written

notebooks by E. Sucksdorff

RC4: "The description of data recovery needs more details. What is the ultimate source of information on the number of those (about 400) photographs that are not found? Maybe some observatory or personal notebooks of E. Sucksdorff (ES)."

Reply: The main sources of information about the history of auroral images taken at SGO are hand-written notebooks of Eyvind Sucksdorff for 1927–1929. There are described relevant data for each photograph (date, exposure time, orientation of camera etc.). In Appendix A there is a table showing the dates of rescued auroral photos as well as the lost ones (see below) based on Sucksdorff's notebooks.

RC4: "These source documents should all be described, scanned and made publicly available in digital format. Even better if they were read to digital tables. Now nothing of such possible development is mentioned. Similarly, the photographs should be scanned and stored in a public digital archive."

Reply: The original source information is stored in tables and auroral images available have been digitized. They are in the digital archive of the SGO. However, for the moment our policy of releasing the auroral data is restricted to individual requests only which should address to the SGO (eija.tanskanen@sgo.fi).

RC4: " How does the image timing go? Judging from the temporal time evolution of auroral forms and intensity depicted in the 6 images, a likely order is clockwise from top left to end at middle left."

Reply: The image order in the plate of six single photographs was clockwise.

RC4: "As described in the manuscript, there was a vigorous photography program in Norway, which led to the improved determination of auroral height. In this situation, I was left wondering why at all Norwegians wanted to install a station in SGO? Historical order of events is missing. "

Reply: There was a plan promoted by the scientific community in Norway that the auroral photography network will be expanded outside Norway for the coming Polar Year 1932–1933. Stations in Greenland, North-Norway (Tromsö) and on Bear Island in the Arctic Sea were set up. The SGO observatory was located far away in the east from the sites of the Norwegian auroral program and could allow a more wide observation view for the auroral photography during the Polar Year.

Eyvind Sucksdorff visited Störmer's auroral laboratory in 1938 and discussed there about auroral research but no common writings exist.

RC4: "Have SGO photographic films been saved and archived in Norway?"

Reply: According to Sucksdorff's notebooks there are comments that images from Sodankylä and from the auxiliary station were sent to Oslo for further analysis. I have been in contact to Oslo University and asked if they have auroral images from the SGO but without results.

RC4: "Visual auroral observations by ES from 1932 to 1944 are said to be archived at SGO. What does it practically mean? "

All observations with related information (observer, time, location, coding, weather info etc.) must be made publicly available with related URLs included. Similarly for the "routine" observations from 1914 until 1954. What about the auroral observations by the Danes? Are these included in the same dataset?"

Reply: Results of visual auroral observations 1932–1944 carried out at the SGO and several sites in Lapland are in hand-written notebooks only. We have plans to transcribe the results in form of tables and make summaries of the observations. There are about 10 rather unorganized notebooks available including the visual observations carried out by the Danish team.

RC4: " Line 29. Contribution by ES was pioneering probably only in Finland."

Reply: This is rewritten: In Finland, Eyvind Sucksdorff´s contribution to research of auroras was a pioneering effort with minimal resources.

RC4: " Lines 83 and 89. Is frame = photograph? If yes, ignore "frame". Does 600 photographs mean 100 plates?

Reply: Yes, "frame" is changed to "photograph". Yes, c. 600 photographs mean c. 100 plates.

RC4: " Line 94. 200 photographs means about 35 paper sheets? How many exactly?

Reply: The paper copies of single photographs are larger than the originals in a plate. The size of a single paper photograph is about 4 x 4 cm. Each paper sheet consists of 10 single photographs. The number of sheets is 20.

RC4: " Statement (see lines 149-151) "The second greatest magnetic storm during this cycle, as recorded by magnetometers at Sodankylä.” "The second greatest magnetic disturbance." would be a possible statement once authors define exactly, how the intensity estimate was made, perhaps based on the local K index? "

Reply: The lines 149-151 are rewritten as follows: The February 27, 1929 magnetic storm observed at the SGO and other magnetic stations at high latitudes was one of the major magnetic storms during the solar cycle 16 (1923–1933) (e.g., Goldie, 1929; Rowland, 1929).

RC4: " Also, additional evidence on storm evolution is needed to verify if the disturbance of the previous night was part of the same storms. Surely it was not "a minor storm".

Reply: Corrected: The February 27, 1929 magnetic storm at the SGO started already in the evening hours of February 26 and ended near midday of 28th (Fig. 5).

RC4: " Fig. 6 caption would read more clearly as follows: "The two top pictures show auroral lights reflected from the frozen river Kitinen. The black belt under the auroral lights, which is the tree line on the other side of the river, is seen in all pictures, most clearly in the top row." This is the setting in all 6 photographs. The exact start and end times (hh:min:sec) of each photograph should be added to the left or right of each panel so that a rough estimate of auroral intensity and temporal order could be obtained. If these images were obtained at 30s intervals, the total time is at most 3.5 min, not 5 min as in text. "

Reply. The caption is rewritten as follows:

            Figure 6. Auroral displays on February 27, 1929 as captured by a camera at           the Sodankylä observatory. Each frame on the photographic plate represents       auroras in intervals of about 30 seconds at about 20 h (UT) to the west. The          exposure time varies between 1 to 30 seconds. The first photograph is on the   top left.

            The two top pictures show auroral lights reflected from the frozen river     Kitinen. The black belt under the auroral lights, which is the tree line on the       other side of the river, is seen in all pictures, most clearly in the top row.

            Next four pictures show rapidly changing auroral forms, veils and spirals. Two      bright spots are planets Jupiter (upper) and Venus (lower) in the west and          about 15° from the horizon.   (Photo: E. Sucksdorff¨s collection SGO).

The total time (about 5 min) is corrected: about 3.5 minutes.

RC4: " The exact start and end times (hh:min:sec) of each photograph should be added to the left or right of each panel so that a rough estimate of auroral intensity and temporal order could be obtained. "

Reply:  They will be given later. There are some problems with Sucksdorff's time writings during the storm.

RC4: " Figure 8. While the number of auroral nights gives some information about the occurrence of auroras, the more correct way is to present the fraction of the nights with auroras to the number of all nights that were "available" for auroras to be observed. So, in addition to the figure of absolute numbers, authors should present these fractions. Otherwise, the study is rather futile. As seen in the figure, there are times when auroral occurrence and magnetic activity are very different, even differently located over the cycle. Also, the multi-decadal rise is dubiously large in auroras. These differences are, very likely, due to the variable weather conditions, which would be corrected by the above fractions."

Reply: We have added new data to the auroral data shown in Fig. 8 (see below) The data is taken from the compilation of visual auroral data by Legrand and Simon (1987). The data collection comprises of several thousands auroral records from sub-auroral latitudes in the northern hemisphere from the years 1780–1979This data series correlates reasonable well with the time variation of auroras obtained form the SGO during 1914–1954. However, there are certain anomalies in the SGO curve when magnetic activity and auroral occurrence are quite different due probably varying weather and cloudy conditions. The original conclusion that there has been an increasing trend in the occurrence of aurora 1914-1954 at SGO is still valid.

[Legrand, J.-P.  and Simon, P.A., 1987. Two hundred years of auroral activity (1780–1979). Annales Geohysicae, 5, 161–167].

There is a picture attached in the end of the reply sheet showing the correlation between global aa-index and auroral occurrence number derived by Legrand & Simon. The linear correlation for the years 1914–1954 is +0.79.

RC4: "Mention in text and in caption what is the magnetic activity index used here."

Reply: The magnetic activity index is the annual mean of daily Ak number taken from the magnetic yearbooks of the SGO.

RC4 line 205. "Line 205. Mention which observatories."

Reply: The two temporary observatories during the Polar Year 1932-1933 were Petsamo (69.5°N; 31.2°E) near the coast of the Arctic Sea, now in the territory of Russia, and Kajaani in East-Finland (64.2°N; 27.7°E).

RC4: " Line 241-242. This is an odd sentence. Auroral occurrence studies are also part of auroral studies."

Reply: This sentence is now: Independent from auroral studies, Visual observations of the occurrence of auroras were made in connection with daily meteorological observations at the Sodankylä observatory since the founding of the observatory in 1914.

RC4: " Line 156. Ref to Fig. 5 must be earlier in text.

Reply: Corrected

RC4: " Line 254. It is multi-decadal, not decadal."

Reply. Ok. Corrected.

RC4: " Line 272. Write: auroras obtained almost one hundred years ago are the first ones in Finland."

Reply: Ok. Corrected

RC4: " References are relevant except for all the three papers by Tanskanen. Neither Tanskanen et al., 2005, nor Tanskanen, 2009, deals with auroral observations. "

Reply: Tanskanen et al. (2005) and Tanskanen (2009) found that the largest substorm numbers and peak amplitudes were found during the declining solar cycle phases. Their analysis was derived using magnetic data from the solar cycle 1993–2003. This similar to conclusion here that auroral occurrence rate is generally enhanced during the declining phase of a solar cycle.

RC4: "  Tanskanen, 2022, is not even a scientific paper. "

Reply: Ok. This reference is deleted.

RC4: " The centennial increase in geomagnetic activity was found by Mayaud in 1972".

Reply: Yes. The reference Mayad (1972) is added in the reference list.

Mayaud, P.N.: The aa Indices: A 100-Year series characterizing the magnetic activity. Journal of Geophysical Research, 77, 6870–6874, https://doi.org/10.1029/JA077i034p06870, 1972.

Appendix A

_________________________________

Table 1a. Dates¹ of available auroral photographs

at the SGO 1927–1929

________________________________________

Date                  Number of single photos

1927

Nov 18                          24

Nov 19                           6

Dec 13                           33

Dec 14                            3

Dec 18                            6

Dec 28                           42

1928

Jan 27                           46

Mar 11                          18

Mar 13                          30

1929

Feb 27                           18

Total                             226

______________________________________

Table 1b. Dates¹ of photographs lost

in the war 1944

______________________________________

Date                  Number of single photos

1928

Dec 6                              9

1929

Jan 29                           18

Feb 17                           11

Feb 27                           147

Mar 7                            12

Mar 8                            40

Mar 11                          42

Mar 14                          78

Mar 27                          27

Total                             384

_____________________________________

¹ The data is based on original hand-written

notebooks by E. Sucksdorff

Corrections to Fig. 6. (Magnetic storm Feb 27, 1929)

The corrected times (UT hh:mm:ss) for the six photographs  and the exposure times (in brackets) are as follows:

1st row from left to right: 18:28:01 (16), 18:28:39 (8),

2nd row: 18:28:57 (11), 18:29:38 (11)

3rd row: 18:31:04 (9), 18:32:40 (12)

Total time 4 min 19 sec