Variabilidad y Reconstrucción
del Clima

Lunes, 15 de Julio del 2024

INCITE: Western North Pacific Summer Monsoon

Reconstructing the Western North Pacific Summer Monsoon since the late the nineteenth century

A new index, the Western North Pacific Directional Index (WNPDI), based on historical wind direction observations taken aboard sailing ships has been developed to characterize the Western North Pacific Summer Monsoon (WNPSM) since 1898. The WNPDI measures the persistence of the surface westerly/easterly winds in the [100−130E; 5−15N]/[110−140E; 1820−30N] regions, exhibiting a consistent relationship with the summer precipitation in the areas affected by the WNPSM throughout the entire 20th century. Its length doubles that of the previous WNPSM index (1948-2014) based on reanalysis products, which allows uncovering different relevant features of the WNPSM variability.

The WNPSM had a significant interdecadal variability along the 20th century. In particular, the period 1918-1948 was characterized by less variable and stronger monsoons than in recent decades. Additionally, the relationship between the WNPSM and ENSO or El Niño Modoki has been evaluated during the entire 20th century for the first time. It is confirmed that the WNPSM tends to be strong (weak) when El Niño (La Niña) develops during the whole record. Nevertheless, the relationship during the ENSO decaying phase is not stable in time. Thus, the WNPSM tended to be strong (weak) when La Niña (El Niño) decayed only since the late-1950s with an opposite relationship in the earliest part of the record. El Niño Modoki shows a rather stable and high correlation with the WNPDI during the whole study period throughout the 20th century.

Key Words: WNPSM; ENSO; climate variability; reconstruction; logbook

Reference: Vega, I., D. Gallego, P., Ribera, F. de Paula Gómez-Delgado, R. García-Herrera and C. Peña-Ortiz, 2018: Reconstructing the Western North Pacific Summer Monsoon since the late nineteenth century. Journal of Climate, 31, 355-368, doi:10.1175/JCLI-D-17-0336.1

Figure 1: Standardised seasonal (JAS) WNPDI between 1849 and 2014 and seasonal average. Shaded curve is computed as a robust locally weighted regression with a 31-year window.

The WNPDI series can be downloaded HERE.

Imbalaced classification techniques for monsoon forecasting based on a new climatic time series

Monsoons have been widely studied in the literature due to their climatic impact related to precipitation and temperature over different regions around the world. In this work, data mining techniques, namely imbalanced classification techniques, are proposed in order to check the capability of climate indices to capture and forecast the evolution of theWestern North Pacific Summer Monsoon. Thus, the main goal is to predict if the monsoon will be an extreme monsoon for a temporal horizon of a month. Firstly, a new monthly index of the monsoon related to its intensity has been generated. Later, the problem of forecasting has been transformed into a binary imbalanced classification problem and a set of representative techniques, such as models based on trees, models based on rules, black box models and ensemble techniques, are applied to obtain the forecasts. From the results obtained, it can be concluded that the methodology proposed here reports promising results according to the quality measures evaluated and predicts extreme monsoons for a temporal horizon of a month with a high accuracy.

Reference: Troncoso, A., P. Ribera, G. Asencio-Cortés, I. Vega and D. Gallego, 2017: Imbalaced classification techniques for monsoon forecasting based on a new climatic time series. Environmental Modelling & Software , 106, 48-56, doi:

© I.Vega 2017