Wirbelsturmaktivität in Asien durch El Nino und solare Schwankungen kontrolliert

Wirbelstürme in Asien werden als Taifune bezeichnet. Wie hat sich die Taifun-Aktivität in den letzten Jahrzehnten und Jahrhunderten entwickelt? Gibt es Trends? Wir begeben uns auf einen Streifzug durch die neuere Literatur. Wie alle unsere Beiträge, wird auch dieser Blogartikel in ein paar Wochen in unserem thematischen Inhaltsverzeichnis zu finden sein. Wenn also das nächste Mal ein Taifun in Asien wirbelt und ein Aktivist umgehend den Klimawandel dafür verantwortlich macht, haben Sie den wichtigen klimahistorischen Kontext sofort parat.

Wir beginnen in Japan. Yamashita & Mitsumata 2013 analysierten die Taifunstatistik der letzten 70 Jahre und berichteten eine Abnahme der Taifune, wobei Japan selber aber offenbar von immer mehr Wirbelstürmen getroffen wurde. Seit 1980 gab es keine Veränderungen mehr. Abstract:

Does Global Warming Affect Typhoon Patterns in Japan? Discussion from the Viewpoints of the Numbers of Typhoons That Develop, Approach, and Hit Japan, and Their Intensities
The present paper examines the theory that global warming causes abnormal weather phenomena involving typhoons, focusing on the numbers of typhoons that develop and hit Japan and their intensities. According to records, since 1980, there has been a decrease in the annual number of typhoons that develop during the year, whereas there has been an increase in those that approach and hit Japan. The annual number of typhoons since 1980 is the same as in the period between 1951 and 1960. The numbers of typhoons that approached and hit the country were the highest during the period from 1951 to 1970, and started to decline between 2001 and 2010. When compared to the data on the numbers of typhoons that developed, approached, and hit Japan during the period from 1951 to 1970, there have been no significant changes since 1980. Data on the monthly numbers of typhoons that develop, approach, and hit also suggest that there has been no significant prolongation of the typhoon season or delay in its start. Regarding the intensity of typhoons, there has been no significant change in the mean minimum pressure of typhoons, a decrease in the number of typhoons with a very low minimum pressure, and no significant increase in the number of typhoons with a very large maximum wind velocity.

Weiter in Südkorea und Katsuki et al. 2016. Die Autoren rekonstruierten die Taifunhäufigkeit für die Zeit 1400-1900 n. Chr. und fanden Schwankungen, die eng an den Ozeanzyklus El Niño/Southern Oscillation (ENSO) gekoppelt waren. Zudem entdeckten sie einen Bezug der Taifune zur Variabilität des ostasiatischen Sommermonsuns, der wiederum von der Sonnenaktivität gesteuert wird. Zu Zeiten geringer Sonenaktivität gab es mehr Wirbelstürme, da sich der Monsun verstärkte. Abstract:

Factors controlling typhoons and storm rain on the Korean Peninsula during the Little Ice Age
Documenting multi-decadal typhoon and storm-rain variability is useful to prevent future typhoon and flood disasters. We present the history of typhoon and storm-rain activity in East Asia inferred from multi-proxy analyses of Lagoon Hwajin-po sediments along the eastern coast of Korea. Anthropogenic effects were enhanced in Lagoon Hwajin-po since ca. AD 1900, by increasing farming in the catchment. To avoid these human-induced effects, we reconstructed the history of typhoon and storm-rain activity only for the interval AD 1400–1900. The record indicates that typhoon frequency throughout the Korean Peninsula varied in response to the state of the El Niño/Southern Oscillation. Typhoon variability was likely modulated further by the state of the East Asia summer monsoon (EASM) pattern, associated with variation in the magnitude of solar irradiance. During periods of minimum solar activity, such as the early Maunder Minimum (AD 1650–1675), typhoons struck the east China coast and Korean Peninsula more frequently because of a strengthened EASM.

Ein Jahr später legten Katsuki et al. 2017 nach. In einer Studie aus Korea für das mittlere Holozän, also für die Zeit vor einigen tausend Jahren, identifizierten sie wiederum ENSO-Ozeanzyklen sowie solare Schwankungen als Auslöser der Taifun-Variabilität. Die Autoren vermuten, dass die solaren Aktivitätsschwankungen den westlichen Jet Stream beeinflussen, der dann wiederum die Stürme verändert.

Multi-centennial-scale changes in East Asian typhoon frequency during the mid-Holocene
This study reconstructs a record of typhoon frequency over the Korean Peninsula during the mid-Holocene using mineral components and diatom assemblages in deposits of Lagoon Hyangho, located on the east coast of the peninsula. The lagoon deposits confirm the occurrence of cyclical, multi-centennial scale episodes of low salinization induced by typhoon-derived heavy rain. Although shifts in typhoon frequency broadly follow El Niño/Southern Oscillation (ENSO) conditions during the Holocene, evidence from the typhoon-induced deposits in Hyangho Lagoon suggests that the path of the polar westerly jet controls the effect of ENSO on multi-centennial-scale typhoon patterns across the mid-latitude region of East Asia. The influence of ENSO is limited when the westerly jet passes through low latitudes. Fluctuations in solar activity play a key role in regulating movement of the westerly jet. Multi-centennial scale changes in typhoon frequency in mid-latitude East Asia are, therefore, influenced by changes in solar activity and ENSO conditions.

Nun nach Taiwan und Wang et al. 2014. Dort rekonstruierten die Autoren die Taifunhäufigkeit, die währen kalter Phasen wie der Völkerwanderungszeit und der Kleinen Eiszeit zunahm. Abstract:

Late Holocene environmental reconstructions and their implications on flood events, typhoon, and agricultural activities in NE Taiwan
We reconstructed paleoenvironmental changes from a sediment archive of a lake in the floodplain of the Ilan Plain of NE Taiwan on multi-decadal resolution for the last ca. 1900 years. On the basis of pollen and diatom records, we evaluated past floods, typhoons, and agricultural activities in this area which are sensitive to the hydrological conditions in the western Pacific. Considering the high sedimentation rates with low microfossil preservations in our sedimentary record, multiple flood events were. identified during the period AD 100–1400. During the Little Ice Age phase 1 (LIA 1 – AD 1400–1620), the abundant occurrences of wetland plant (Cyperaceae) and diatom frustules imply less flood events under stable climate conditions in this period. Between AD 500 and 700 and the Little Ice Age phase 2 (LIA 2 – AD 1630–1850), the frequent typhoons were inferred by coarse sediments and planktonic diatoms, which represented more dynamical climate conditions than in the LIA 1. By comparing our results with the reconstructed changes in tropical hydrological conditions, we suggested that the local hydrology in NE Taiwan is strongly influenced by typhoon-triggered heavy rainfalls, which could be influenced by the variation of global temperature, the expansion of the Pacific warm pool, and the intensification of El Niño–Southern Oscillation (ENSO) events.

Sommerstürme im Indischen Ozean zeigen für die vergangenen 30 Jahre keinen Trend. Dies fanden Cohen & Boos 2014:

Has the number of Indian summer monsoon depressions decreased over the last 30 years?
Monsoon depressions are cyclonic atmospheric vortices with outer radii near 1000 km that form within the larger-scale monsoon circulations of India and other regions. Recent studies have reported a downward trend in recent decades in the number of Indian summer monsoon depressions. In particular, the years 2002, 2010, and 2012 were noted for having the first summers, in over a century, in which no depressions formed. Here satellite and reanalysis data are used to document the existence of multiple storms in the summers of 2002, 2010, and 2012 that meet traditional criteria for classification as monsoon depressions. Furthermore, the number of extreme synoptic events occurring each summer over the Bay of Bengal is estimated from satellite scatterometers and exhibits no statistically significant trend over the last three decades. These results raise questions about the validity of previously claimed large trends in monsoon depression activity in the Indian summer monsoon.

Girishkumar et al. 2014 heben die bedeutende Rolle der ENSO-Ozeanzklik für die Wirbelstürme im Golf von Bengalen hervor. In der warmen (positiven) PDO-Phase treten Wirbelstürme häufiger in La Nina- als in El Nino-Jahren auf. Abstract:

Influence of Pacific Decadal Oscillation on the relationship between ENSO and tropical cyclone activity in the Bay of Bengal during October–December
The relationship between ENSO and tropical cyclones (TCs) activity in the Bay of Bengal (BoB) during October–December under cold (1950–1974) and warm (1975–2006) phase of Pacific Decadal Oscillation (PDO) is investigated. A statistically significant difference in the formation of total number of TCs and intense TCs (Category-1 and above) between El Niño and La Niña years is observed when the PDO was in warm phase. Our analysis shows that, there is a tendency to form more number of TCs during La Niña years (2.62 TCs per season) than during El Niño years (1.6 TCs per season) under warm phase of PDO. Moreover, the difference is quite high for intense TCs cases, such as, relatively more number of intense TCs forms in the BoB during La Niña years (1.4 TCs per season) compared to El Niño years (0.10 TCs per season) under warm phase of PDO. However, the difference in the formation of total number of TCs and intense TCs between La Niña and El Niño years is not significant under cold phase of PDO. Significant enhancement in low level cyclonic vorticity and mid-troposphere humidity during La Niña years compared to El Niño years when the PDO was in warm phase, rather than the PDO was in cold phase leads to this difference. Our analysis further shows that how the ENSO related teleconnection to the Indian Ocean region differ under warm and cold phase of PDO.

Eine Modellierung von Parth Sarthi et al. 2015 prognostiziert im weiteren Verlauf der globalen Erwärmung eine Abnahme der Wirbelstürme im Indischen Ozean:

Possible future changes in cyclonic storms in the Bay of Bengal, India under warmer climate
The aim of this paper is to study the model’s simulated frequency, track, intensity and location of cyclonic storms (CSs) and severe cyclonic storms (SCSs) in the Bay of Bengal (BoB), India. For the purpose, the PRECIS (Providing REgional Climates for Impacts Studies) a regional climate modelling system, of UK Met Office, is used. This model is integrated for the period 1961–1990 (baseline) and the future time period 2071–2100 (High emission scenario, A2). To run the model, the initial and lateral boundary conditions are supplied by UK Met Office. The analysis of frequency, track, intensity and location are carried out for May, June, September and October for the period 1961–1990 and 2071–2100. To evaluate the model’s performance in simulating storms frequency during 1961–1990, chi square test is carried out with observed storms for the same period. The model’s simulated frequency of storms is an overestimation of observations although the frequency of model’s simulated storms during 2071–2100 is less than that of during 1961–1990. In general, model’s simulated storms are found moving in the northwest direction from their initial location in all months during 1961–1990 and 2071–2100. In model’s simulations, the drop in central pressure is relatively more in the months of May, June, September and October during 2071–2100 compared with that during 1961–1990. During 2071–2100, more intense storms may be possible in the months of May and June compared with that of September and October. It is observed that the model is able to simulate the initial locations of storms during 1961–1990 and 2071–2100 close to observations for the months of June and September, especially.

Die nächste Studie kommt aus China. Liu et al. 2017 analysierten die Entwicklung der tropischen Wirbelstürme in China während der letzten 1000 Jahre anhand von historischen Dokumenten über Schiffsunglücke. Sie fanden unterschiedliche regionale Schwerpunkte der Wirbelsturmaktivität die sich in El Nino- und La Nina-Jahren unterschieden.

Insight into tropical cyclone behaviour through examining maritime disasters over the past 1000 years based on the dynastic histories of China – A dedication to Ocean Researcher V
This paper uses China’s historical records to gather information on maritime disasters caused by tropical cyclones. Official records show that there were a total of thirteen major maritime disasters possibly caused by tropical cyclones. Maritime disaster variation trends indicate that tropical cyclones tend to strike the southern coast of China during a La Niña-like stage whereas an El Niño-like stage leads to tropical cyclones being guided northward toward the Korean Peninsula and Japan. During China’s Yuan Dynasty (AD 1271–1368) Kublai Khan tried to invade Japan twice during an El Niño-like stage and encountered intense tropical cyclones, which the Japanese called Kamikaze. During a La Niña-like stage, multiple maritime disasters occurred in the East China Sea, the Taiwan Strait and the South China Sea in the Qing Dynasty (AD 1636–1912). Indeed, the historical record of the Qing Dynasty details maritime disasters at least 9 times. These events were also caused by tropical cyclones. In addition, statistics on the seasons of tropical cyclone genesis and their landfall locations from AD 1945–2013 in the Northwest Pacific Ocean region reveal that in summer, tropical cyclones tend to make landfall along coastal regions north of Fujian Province, eastern China; however, in autumn and winter, cyclones tend to be guided further southward to make landfall in southern China (Hainan), Vietnam, and the Philippines. This phenomenon in seasonal variation is reflected in the maritime disaster events recorded for coastal regions of southeastern China and landfall locations of tropical cyclones during the Qing Dynasty.

Ni et al. 2015 analysierten die tropischen Wirbelstürme auf dem chinesischen Festland für die vergangenen 55 Jahre. Sie fanden ab 1980 eine starke Abnahme der Häufigkeit und Stärke der Stürme.

Climatology and trends of tropical cyclone high wind in mainland China: 1959–2011
The climatology and trends of tropical cyclone (TC) high wind (TCHW; wind speeds ≥10.8 m s−1) in mainland China during 1959–2011 were studied based on a comprehensive series of surface wind observations from 574 stations. Of these stations, 41 were affected by TCHW more than once per year and were mainly located along the southeast coastline or at some inland mountain locations. The contribution of TCHW frequency to high wind (HW; wind speeds ≥10.8 m s−1) frequency was highest along the southeast coastline of China and decreased rapidly at inland locations. Both the TCHW frequency (intensity) and HW frequency (intensity) displayed significant downward (weakened) trends after the 1980s. The proportion of HW events accounted for by TCHW decreased, although the trend was not significant. The changes in TCHW frequency and intensity were associated with variations in the number of influencing TCs (ITC: a TC that causes at least one TCHW event), ITCTs (ITC time: an observation time with ITCs), the range of ITC influence, and ITC intensity and track. The annual number of ITCs and ITCTs declined consistently during the study period. The range of ITC influence as related to the TC size in 1983–2011 was smaller than in 1959–1982. The variation of the percentiles of ITC intensity showed an increasing (decreasing) trend of weaker (stronger) ITCs. Years with the maximum TCHW frequency had more ITCs and ITCTs than those with the minimum TCHW frequency.

Dazu passt die folgende Pressemitteilung der Penn State University vom 17. Februar 2017. Die Forscher fanden für China seit 1960 eine Halbierung der Sturmtätigkeit:

Study shows China’s severe weather patterns changing drastically since 1960
In one of the most comprehensive studies on trends in local severe weather patterns to date, an international team of researchers found that the frequency of hail storms, thunderstorms and high wind events has decreased by nearly 50 percent on average throughout China since 1960.

The team analyzed data from the most robust meteorological database known, the Chinese National Meteorology Information Center, a network of 983 weather observatories stationed throughout China’s 3.7 million square miles. Meteorologists have been collecting surface weather data through the network since 1951 or earlier, which provided the researchers an unprecedented look at local severe weather occurrences. “Most of the data published on trends in severe weather has been incomplete or collected for a limited short period,” said Fuqing Zhang, professor of meteorology and atmospheric science and director, Center for Advanced Data Assimilation and Predictability Techniques, Penn State. “The record we used is, to the best of our knowledge, the largest, both in time scale and area of land covered.”

The team, who report their findings today (Feb. 17, 2017) in Scientific Reports, found that the strength of the East Asian Summer Monsoon decreased at a rate strongly correlated to that of severe weather throughout the same time period. The monsoon is an annually recurring, long-term weather phenomenon that brings warm, moist air from the south to China in the summer, and cooler air from the north to China in the winter. A monsoon’s strength is measured by calculating the average meridian wind speed in this area. “We believe that changes in monsoon intensity are affecting severe weather in the area because of the strong correlation we found, but we cannot say the monsoon is the exclusive cause,” said Zhang. “A monsoon is one of the major drivers of severe weather because it affects the three necessary ‘ingredients’ for severe weather, which are wind shear, instability and triggering.”

Wind shear is the difference between the wind speed and direction at different altitudes. Because a monsoon brings southerly winds into China, a weaker summer monsoon would decrease the overall low tropospheric wind shear. The weaker monsoons would also bring less warm, moist air from the south — one of the most common sources of instability in the atmosphere. A common triggering mechanism for severe convective weather is lifting by the front, a high temperature gradient across the monsoon, and this would also be reduced in a weaker summer monsoon.

Some studies suggest that climate change may be one of the reasons that the Asian Summer Monsoon weakened. One factor in monsoon formation is the difference between the temperature above land and the temperature above adjacent ocean or sea. A warming climate would affect the difference between these two and, as a result, simulations show that this could continue decreasing the monsoon’s strength. However, the team noted that other major changes in the area — such as an increase in industrialization and air pollution in China in the 1980s — might have played a significant role in the region’s atmospheric changes and could affect the severe weather.

While a decrease in severe weather might sound beneficial, it may not always be a good thing. “There are many natural cycles that rely on severe weather and the precipitation it brings,” said Qinghong Zhang, professor of atmospheric and oceanic sciences, Peking University, lead author of the study, who conducted this research while on sabbatical at Penn State. “A decrease in storms could potentially lead to an increase in droughts. Also, some theorize that while the frequency of severe weather decreases, their intensity could potentially increase. We cannot say if this is true yet, but it is something we will analyze in the future.”

This was the first study in its level of detail because of the amount of data collected by the Chinese National Meteorology Information Center. The study also showed that occurrences of hail remained relatively steady from 1961 through the 1980s before plummeting. “The frequency of thunderstorms and high winds decreased gradually over the time period we studied, but not hail,” said Qinghong Zhang. “This is something we don’t fully understand at this point but plan to investigate more.” Xiang Ni, doctoral student, Peking University, contributed to this study. The Chinese National Science Foundation, the National Basic Research Program of China and the U.S. National Science Foundation supported this research.

Während die Stürme in China und anderen Orten Asiens abnehmen, ist auf den Philippinen in den letzten 60 Jahren eine Zunahme verzeichnet worden, wie die Unversität Sheffield 2016 mitteilte.

Fazit: Der klimahistorische Kontext ist erneut entscheidend, um zunächst die Sturmvariabilität und ihren Antrieb zu verstehen. Ozeanzyklen und Sonne sind wichtige Treiber, die in den Modellen noch nicht korrekt erfasst sind. Die Lage und Intensität der Jetstreams könnte ein Schlüssel zur solaren Klimabeeinflussung werden. Ist es wirklich die Kälte, die die Taifune in Gebieten wie Taiwan häufiger werden lässt, oder eher die schwache Sonnenaktivität, die den Jetstream verändert? Food for Thought.