JCDP

Early systematic meteorological observations in Japan

Masumi Zaiki and Gunther Konnen

The observations were taken at Dejima by the Chief of the Trade Factory, J. Cock Blomhoff for 1819-1823 and then by the medical doctor P.F. von Siebold for 1825-1828 and are of air temperature, and of pressure and humidity. The data by Blomhoff are in von Siebold’s handwriting and apparently copied by him from an older document. The data by von Siebold for 23 Sept 1827-1828 are in two versions: one apparently being the originals in his own handwriting and a copy by an anonymous copyist. For the period Jan-Dec 1825, there were parallel readings in Tokyo (Figure); von Siebold also observed during his journey from Nagasaki to the Palace of the Shogun in Edo (now Tokyo) during Mar-July 1826.

Thermometer readings were made in full degrees Fahrenheit. In the period 1819-1822, the temperature sometimes refers to readings inside the building also. Pressure is recorded only in the von Siebold period. The von Siebold pressure readings after 22 Sept 1827 were in English inches (a unit of 2.5400 cm) divided in decimals. However, the von Siebold readings Nov 1826-22 Sept 1827 are in non-English inches, which are divided in lines according to the duodecimal system (12 lines = 1 inch). From the heights of the barometer we inferred that the unit refers to French inches (a unit of 2.7070 cm).

In the 1819-1828 observations, only von Siebold recorded air humidity. It was measured by his home-made hygrometer ‘manufactured from a hair of a Japanese beauty, which was scalded in soda and then in pure water’.

The pressure and temperature observations were usually taken three times a day, referred to as ‘Morgen’, ‘Mittag’, and ‘Abend’ (morning, midday and evening). There is no explicit mention of the observation hours in the von Siebold documents. Fitting to the annual mean diurnal course of Nagasaki Observatory III 1978-1999 reveals an observation schedule 6:00, 12:00 and 22:00 Local Time (LT), where Dejima LT = UTC + 8:40.

A primary problem of the early instrumental period is the poor coverage outside Europe in the early 19th and 18th centuries. Among the many blank spots is Japan, where the official meteorological network by JMA started in the 1870s. These Blomhoff/von Siebold records extend its start back from 1878 to 1819, the significance of the data reaches further than just an extension of the Japanese instrumental record back in time. First, the recovered series happens to be in a region of the Earth that is poorly covered by instrumental data; second, it overlaps with the long daily series of visual weather reports as documented in diaries of Japanese administrators during the Edo period (1603-1868) at many places in Japan.

03/16/2018

Topics

Anomaly maps in “Climate Atlas”

　　　　　　　　　　　　　　　　　　　　　　　
Junpei Hirano

In climatology, we use values called “anomalies” to understand the average state of climatic elements (atmospheric pressure, temperature, precipitation, sunshine duration, and solar radiation, etc.). The “normal” is defined as the average value of climatic factors during the past 30 years. Since the average value changes due to climate change such as global warming, the normal is updated every ten years. For example, for the 10-year period from 2011 to 2020, the 1981-2010 average was used as the “normal,” but it was updated in 2021, and for the 10-year period from 2021 to 2030, the 1991-2020 average will be used as the “new normal.

In weather forecasting, the term “warmer (colder) than normal” is sometimes used, but in this case, “normal” refers to the “normal” value of temperature. In other words, the “normal value” of temperature is the standard for evaluating the warmth (coldness), etc. of each year. The difference between the temperature of each year and the normal is called the ” anomaly”. In the case of temperature, a positive anomaly indicates a warmer than normal year, while a negative anomaly indicates a colder than normal year. A map of temperature anomalies shows the distribution of areas with warmer-than-normal temperatures (positive anomaly areas) and areas with colder-than-normal temperatures (negative anomaly areas).

Similar to temperature, precipitation can also be plotted based on the “normal” value. However, in the case of precipitation, anomalies are generally expressed as the ratio of precipitation to the normal (ratio of normal to precipitation). For example, if you draw a precipitation anomaly map for a year with an El Niño or La Niña event, you can see areas with more or less rainfall than normal. Global precipitation anomaly maps for summer (June-August) and winter (December-February) of El Niño events are available on the Climate Atlas “World” page. However, as the basis for the anomalies, we have used the 43-year average for the period 1979-2021, for which precipitation data are available, instead of the 30-year “normal. Green-colored areas indicate areas of higher-than-normal rainfall, while brown-colored areas indicate areas of lower-than-normal rainfall. It can be seen that in El Niño years, there is more rainfall in the eastern tropical Pacific and less in the western tropical Pacific.

Furthermore, by comparing the precipitation anomaly map with the SST anomaly map, we can see the relationship between SST anomalies and precipitation anomalies. For example, in the “Winter DJF SST anomaly map for El Niño years”, the eastern tropical Pacific is colored red, indicating that SSTs are higher than normal. In an El Niño year, the sea surface temperature in this region is high, which activates cumulus convection and leads to heavy rainfall.

Global precipitation anomaly maps for summer (June – August) and winter (December – February) La Niña years show the opposite pattern (heavy rainfall in the eastern tropical Pacific and less rainfall in the western tropical Pacific). In La Niña years, sea surface temperatures (SSTs) drop below normal in the eastern tropical Pacific (see SST anomaly distribution in La Niña years), which suppresses cumulus convection and results in less rainfall.

The JCDP “Climate Atlas” will include various climate anomaly maps in the future. We recommend that you use the anomaly maps in the JCDP Climate Atlas when explaining “extreme weather” and its spatial distribution in high school geography and geology courses and in university liberal arts courses.