ABSTRACT
This chapter describes spatial and temporal patterns identified in instrument-measured data, and indications of past Pacific decadal–multidecadal variability found in paleoclimate proxy data. It also describes hypothesized mechanisms, including effects of low-latitude volcanic eruptions, and their simulations by a variety of models. The chapter provides an introduction to serendipitous discoveries of sea-level pressure oscillations at interannual and longer timescales mainly in the Pacific region. In a land that had experienced multiyear droughts and famines for centuries, and suffered tragic deaths of millions of its people, the decades of 1860s and 1870s Current Era (CE) were particularly bad for India. The British colonial government was besieged by these calamities and decided to set up a government department to find ways to predict monsoon rains well in advance, so that mitigating measures could be applied. The India Meteorological Department was thus founded in September 1875 CE.
