Were Noctilucent Clouds Caused by the Krakatoa Eruption? a Case Study of the Research ^ ^ Problems Before 1885

Were Noctilucent Clouds Caused by the Krakatoa Eruption? A Case Study of the Research ^ ^ Problems before 1885

Wilfried Schroder Bremen-Roennebeck, Germany

ABSTRACT

It is known that noctilucent clouds were first observed in 1885, two years after the great Krakatoa eruption in the Sunda Straits. The preeminent question of whether noctilucent clouds appeared before 1885 is studied here in detail. Using various literature sources and observational records for the nineteenth century from several observers it can be shown that before 1885 noctilucent clouds were never described in the literature. The so-called bright nights or Leuchtstreifen phenomenon was well known in the nineteenth century, but no observer described any structures that can be identified as noctilucent clouds. This result makes it clear that the noctilucent clouds seen in 1885 were the first such observations to be made. A possible increase in frequency of occurrence can be estimated from the year of discov- ery up to the present day.

1. Problem that were available to him from the Northern and Southern Hemispheres, and he began research on the A fundamental feature in understanding the nocti- height, dynamics, and nature of the clouds. lucent clouds and the problems of a possible mesos- Since that period (1885-96) the attention given to pheric change is the question of the timing of the first the clouds has varied from time to time. For some years sightings of these clouds (cf. Schroder 1971, 1975; only sporadic data are available. But in more recent Thomas et al. 1989). In 1883 the great eruption of the years, scientists from Russia and Germany have stud- Krakatoa volcano occurred. After its explosion intense ied the clouds so that more than 1000 observations are twilight phenomena were observed all over the world. available. From analysis of the latest data it seems that In Europe many beautiful colors in the morning and the frequency of occurrence of these clouds has in- evening sky were seen and described (Bezold 1906; Jesse creased. This has been discussed in detail by Thomas 1885; Foerster 1906). Furthermore, Bishop's ring and et al. (1989) and Thomas (1996). other phenomena were discovered (Kiessling 1885a). From these studies noctilucent clouds have been In 1885 observers reported the existence of silvery interpreted as one of the indicators of atmospheric glo- clouds that appeared in the evening sky; they were well bal change. Therefore it is important to have more in- defined with ripples and some wave structure. Some sight into the real observational situation before 1885. days later, Otto Jesse, an astronomer at the Berlin Ob- servatory, and many other observers in Germany also watched these clouds in the evening sky. Since those 2. The observers observations, Jesse documented and sampled all data In the nineteenth century geophysics did not exist as a scientific discipline and no regular upper- Corresponding author address: Wilfried Schroder, Hechelstrasse atmospheric studies were made. Geophysical data 8, D-28777 Bremen-Roennebeck, Germany. and observations were collected by astronomers, In final form 20 April 1999. meteorologists, and physicists according to their own ©1999 American Meteorological Society particular interests in the field. At that time an inter-

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Unauthenticated | Downloaded 10/04/21 04:40 AM UTC national network existed following the ideas of tant international scientific programs were started Humboldt and GauB. Furthermore, many astronomers in the nineteenth century: the coordinated measure- were interested in the earth's atmospheric physics (be- ment of electromagnetic field by the Gottinger cause at this time the professions of meteorology and Magnetischer Verein and the worldwide observations geophysics did not exist). The network of the during the First International Polar Year (1882-83) Gottingen Magnetic Verein and its worldwide observ- (cf. Schroder 1991). Although the first project focused ing stations numbered more than 50; scientists in the on the collection of geomagnetic data, anomalous sky network studied geomagnetic problems and atmo- phenomena such as auroras were also observed. The spheric phenomena in general. This was done in both second project dealt mostly with the aurora borealis the Northern and Southern Hemispheres (Schroder from high to midlatitudes; twilight studies were also 1999). It should be noted that in general an observer made. The Polar Year observations were obtained had the chance to note a noctilucent cloud if it existed, from more than 100 stations on land and sea in the but that was not the main research focus. Two impor- Southern and Northern Hemispheres. Auroras were studied in both hemispheres. Fur- ______thermore, regular observations of twilight and airglow were made. In TABLE 1. Twilight phenomena and volcanic activity in the nineteenth century (examples). this connection some 100 scientists observed the sky on different dates Date Place Observations and times throughout the entire year. In the period 1882-83 no re- 1815 Sumbawa (8°S) No anomalous phenomena ported atmospheric phenomena 1821 France (~45°-50°N) Ununsual color of the evening sky; showed a relation to noctilucent England (~50°-55°N) white fog clouds; therefore it can be concluded that there were no noctilu- Aug 1822 Aleppo (~36°N) Sky as in fire cent clouds observed in the years before the Krakatoa eruption. Some Jul 1828 Marburg (~50°N) Sky color phenomena observers also studied twilight Jul 1829 Hungary (~46°-48°N) Red clouds phenomena; data were collected by Bezold (1906), Riggenbach Jul 1831 Volcanos/Sicily (~38°N) No NLC; color phenomena, increased (1886), Necker and Bravais (see twilight (many European places) Riggenbach 1886), Jesse (1885, 1886), Kiessling (1885a,b), Aug 1831 Central America Increased sun colors; sun in various Schmidt (1865), and Hellman (~0°-20°S) color (1884). These people were all good 1859 Australia Unusual twilight observers, generally being astronomers or physicists. During this 1860 Mount Baker (~49°N) Great eruption and ashes; no unusual time, auroral data were also com- remarks on clouds piled by H. Fritz in his catalog 1861 Dschebbel (Africa) Great ash fallout (no unusual (1873). remarks) It is of interest to note that the study of twilight as a scientific 1861 Vesuv (~39°N) Twilight unusual problem was important in the on- 1862 Makjan Island Makjan vanished; no going research of the nineteenth atmospheric remarks century. Furthermore, interest in solar-terrestrial physics, especially 1863 Klot (Java; ~5°-10°S) Sky red, great ash fallout in auroral data, increased at this time (Schroder 1987, 1991). All 1863 Etna (~37°N) Ash rain these points emphasize that there Jul 1880 Cotopaxi (~0°-5°S) Green sun, increased twilight and were different interests in and on- colored sky going scientific investigations of the terrestrial atmosphere as far

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Unauthenticated | Downloaded 10/04/21 04:40 AM UTC TABLE 2. Bravais's twilight observations. Please note that no TABLE 3. Jesse's compilation of noctilucent clouds (NLC) since noctilucent clouds have been described. 1884.

Date Sky Year Remarks 4 Aug 1842 Red band, small yellow and green bands 1883 (~52°5N) Twilight observations: No NLC 5 Aug 1842 Cirri in green sky, red colors in west 1884 (~52°5N) Twilight observations: No NLC 6 Aug 1842 Low red colors 1885 (~52°5N) 23 Jun: NLC 8 Aug 1842 Normal twilight colors 24 Jun: NLC 9 Aug 1842 Twilight 25 Jun: no NLC 10 Aug 1842 Normal twilight colors 27 Jun: NLC 12 Aug 1842 Red twilight colors 28 Jun: no NLC 13 Aug 1842 Red clouds in the west, sky background 30 Jun-2 Jul: NLC yellow 6 and 7 Jul: NLC 14 Aug 1842 Red, yellow, and green colors 8 and 9 Jul: NLC 15 Aug 1842 Red in the east 10 and 11 Jul: no NLC 17 Aug 1842 Clear sky, normal twilight phenomena 13 Jul, 16 Jul: no NLC 30 Aug 1844 Normal twilight phenomena 17 Jul: NLC Source: Riggenbach 18 Jul: no NLC 19 Jul: NLC back as the nineteenth century. This is important to con- sider when attempting to explain why noctilucent 21 Jul: NLC clouds were not observed before 1885. 22 Jul: NLC

3. Observations of noctilucent clouds 26 Jul: no NLC 28 Jul: NLC (very bright) The observational data are shown in Tables 1^4. It is clear that "increased" twilight was noted in many cases. 1886-1891 (~52°5N) year-to-year observations in the Color variability of the sky was well known in the Berlin Atmospheric Programme nineteenth century. After various volcanic eruptions, and positive event of NLC increased twilight phenomena were observed over many years (see tables). The descriptions show many variable color phenomena, increased twilight structures, and in 4. Did noctilucent clouds exist before some cases the so-called bright nights. These data pro- 1885? vide good insight into the twilight and night sky variability, but only in terms of regular and irregular color If we use noctilucent clouds as first indicators of phenomena in the sky. No noctilucent clouds can be iden- atmospheric global change (Schroder 1971; Thomas tified from the descriptions in these reports before 1885 et al. 1989; Thomas 1996) the question arises, were (cf. Table 4). they described or did they even exist prior to 1885? This is a difficult question because no clear nomen-

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Unauthenticated | Downloaded 10/04/21 04:40 AM UTC clature of twilight features exists. Nevertheless, if they (1883-85), remarkable twilights and skyscapes of had existed they almost certainly would have been colors were noted by European observers. noted in some fashion. Noctilucent clouds show strik- Using data currently available, we can say that ing features (waves, ripples, white-blue color, etc.); noctilucent clouds were first observed two years after they are most impressive spectacles in the sky. In gen- the giant Krakatoa eruption, one of the most signifi- eral, noctilucent clouds are distinct from the milky cant geological events in recorded history. Since that way, zodiacal light, or auroras. time the number of noctilucent clouds recorded has It seems very unlikely that experienced observers risen and fallen depending on the attention given to such as Riggenbach, Bezold, Hellmann, Kiessling, them by observers. But it also seems that, as Thomas and Jesse would have overlooked such striking phe- (1996) has suggested, that noctilucent clouds may be nomena as noctilucent clouds. Moreover, Jesse (1886) regarded as indicators of global change in the physi- made systematic twilight observations during the years before 1885. He noted that if there had been noctilucent clouds, he would not have TABLE 4. Development of twilight data after the Krakatoa event (examples). overlooked them. Furthermore, in all the descriptions by the cited ob- Date Place Description servers no remarks are given that show any references to what could 1883* have been noctilucent clouds. From 20 May 1883 ~5°-10°S Krakatoa; various colors in the sky the data presented here it can be 8 Jun Keitum (~54°N) Intense evening red concluded that noctilucent clouds were not observed before 1885 (cf. 30 Jun 33°5N Sun blood red Table 4). 9 Jul 54°4N Increased evening sky It seems that only after the 13 Aug 41°N Yellow sun/red Krakatoa eruption did condensa- 29 Aug 44°N Various colors in evening sky tion nuclei materials reach the upper atmosphere, which is necessary 1884* for the formation of noctilucent 5 Apr 9°S Intense evening red clouds. Krakatoa was one of the 23 Apr Hamburg (~53°N) Evening red greatest volcanic eruptions that has 25 May Rostock (~54°N) Intense evening twilight ever taken place. It catapulted enough water and particles into the 11 Jun Intense purple light, evening rays mesosphere such that—two years 17 Jun 36°N Dark morning, red twilight after the event noctilucent clouds 25 Jun formed. Jesse started an observa- 26 Jun 53°8N Red sun ring (a remarkable tional program in 1885 and in all phenomena) the years (1896-1901) the clouds 8 Jul 41°1N Evening red, morning red were noted. It is of interest that 9 Jul Morning red twilight since 1885 noctilucent clouds have been observed continuously in 13 Jul Increased twilight most years up to the present. 14 Jul Berlin (~52°5N) Bishop's ring, intense light From the investigations by 14 Jul Rome (~52°N) Red ring around the moon Kiessling (1885a,b) it is clear how 5 Jul the volcanic particles reached the Northern Hemisphere over Europe 25 Jul 3°S Red ring around the sun after the event. The most important 27 Jul Shanghai (~32°N) Twilight phenomena with various eruptions were in May and August forms 1883; the first observations of 28 Jul Shanghai (~32°N) Increase morning twilight, various noctilucent clouds occurred nearly colors two years later. In the meantime

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Unauthenticated | Downloaded 10/04/21 04:40 AM UTC cal structure of the mesosphere during recent decades, Hellmann, G., 1884: Beobachtungen iiber die Dammerung. Z Osterr. Ges. Meteor., 19, 57-64, 162-175. a process that is on going. Jesse, O., 1885: Auffallende Abenderscheinungen am Himmel. Meteor. Z, 2, 311-312. , 1886: Die auffallenden Abenderscheinungen am Himmel References im Juni und Juli 1885. Meteor. Z., 8, 64-71. Kiessling, J., 1885a: Uber die geographische Verbreitung des Bezold, W., 1906: Gesammelte Abhandlungen aus den Gebieten Bishop'schen Sonnenrings. Das Wetter, 2, 81-89. der Meteorologie unddes Erdmagnetismus. Vieweg, 448 pp. , 1885b: Die Dammerungserscheinungen imJahre 1883 und Foerster, W., 1906: Von der Erdatmosphare zum Himmelsraum. ihre physikalische Erklarung. Yoss, 64 pp. Hillger, 115 pp. Riggenbach, A., 1886: Beobachtungen iiber die Dammerung, Fritz, H., 1873: Verzeichniss beobachteter Polarlichter. Gerolds, insbesondere iiber das Purpurlicht und seine Beziehungen 255 pp. zum Bishop (schen Sonnering. Habil.-Schr. Univ. Basel, 115 pp. Schmidt, J. F., 1865: Uber die Dammerung. Astron. Nachr., 63, 97-116. Schroder, W., 1971: Investigations on the transitions periods in spring and au- TABLE 4. (Continued) tumn of the mesopause. Gerlands Beitr. Geophys., 80, 65-74. Date Place Description , 1975: Entwicklungsphasen der Erforschung der Leuchtenden Nacht- 1884* wolken (Research on Noctilucent Clouds). Akademie-Verlag, 64 pp. 30 Jul Adelaide (~28°S) Evening red , 1991: The First International Polar 6 Aug 14°3N Evening colors Year (1882-1883) and international geophysical cooperation. Earth Sci. 7 Aug Evening colors Hist., 2, 223-226. 12 Aug 46°N Nice evening red —, 1997: Some aspects of the earlier 18 Aug 40°3N Intense evening red; also at other history of solar-terrestrial physics. places Planet Space Sci., 45, 395^00. —, 1999: The Aurora in Time. Science 21 Aug 40°3N Sun as a "fire ball" Edition. 53°8N Red sun ring on 14, 19, 24, Thomas, G. E., 1996: Global change in the 27 Aug mesospher-lower thermosphere region: Has it already arrived? J. Atmos. Terr. Uppsala (~60°N) Bishop's ring Phys., 58, 1629-1656. Aug Hamburg (~53°N) Evening red at 1, 6, 7, 8, 18, , J. J. Olivero, E. J. Jensen, W. 20 Aug and at other places Schroder, and O. B. Toon, 1989: Rela- tion between increasing methane and 1885 the presence of ice clouds at the meso- 4 May 27°N Intense evening red Bishop's ring pause. Nature, 338, 490-492. very often observed at different places in May 9 May Arnsberg (~53°5N) Bishop's ring 11 Jun Clairvaux Unusual evening twilight (also at 12 Jun) June** Moncalieri 4, 5, 12, and 13 Jun intense evening glow; in June at various places increased colors, forms, and display in the morning and evening sky observed June** Full month; different Increased twilight/evening glow places (Northern Hemisphere) *In May-July at different days and places increased twilight was noted but no noctilucent clouds were described. **On 1, 2, 3, 4, 5, 12, and 13 Jun evening red has been noted, but no noctilucent clouds.

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