After Krakatau: Eurasian Climate and Circulation in Historical Temperature and Pressure Records

Abstract. The impact of the Krakatau eruption on Eurasian climate is still not fully understood. Previous studies have provided insight from seasonal averages and gridded datasets, while the month-to-month evolution and the role of atmospheric circulation remain less clearly resolved. Here, we analyse air-temperature and station-pressure observations from the Annalen des Physikalischen Centralobservatoriums at monthly and daily resolution. The first complete post-eruption year, 1884, was characterised by marked seasonal variability rather than continuous cooling. Mild conditions in January and February were followed by widespread negative temperature anomalies through much of spring and summer, with particularly coherent cooling in April and August. Network-median anomalies in these months were −1.50 °C and −1.91 °C, respectively, both ranking as the coldest among the corresponding reference years. Conditions reversed during autumn, culminating in widespread December warmth, with a network-median anomaly of +2.71 °C, the warmest in the reference-year distribution. Late-summer cooling recurred in August 1885, whereas December warmth was common across much of Eurasia from 1883 to 1886. Simultaneous pressure observations point to a substantial role for atmospheric circulation in the winter anomalies, while the spring and late-summer cooling was not associated with a common pressure pattern. Daily records show that cool conditions could persist for weeks despite changing local pressure differences. The observations therefore indicate strong regional modulation of the post-Krakatau temperature evolution; an additional volcanic influence remains physically plausible but cannot be isolated from the historical station data.