Investigation of the North Atlantic Oscillation and Indian Ocean Dipole Influence on Precipitation in Turkey with Cross-Spectral Analysis

Abdullah Cem Koc,Umut Sakine Demir

doi:10.3390/atmos12010099

Abstract

Predicting the future behavior of precipitation is of the utmost importance for planning agriculture or water resource management and in designing water structures. Determining the relationships between precipitation and the oceans may enable more accurate predictions. Therefore, oceanic and other persistent indices called teleconnection patterns can be used, namely the North Atlantic oscillation (NAO) and the Indian Ocean dipole (IOD). The NAO affects the precipitation patterns in the Atlantic Ocean and Mediterranean countries, such as in Turkey. The IOD is related to temperature and precipitation in the Indian Ocean coastal countries and in some areas far from the Indian Ocean. In this study, the effects of the NAO and IOD indices on precipitation in Turkey were investigated by means of cross-spectral analysis between the monthly total precipitation (mm) and monthly NAO and IOD index values. Phase shift values were also calculated for the selected periods and their accuracy was evaluated statistically, using the determination coefficient (R2) and Akaike information criterion (AIC) as performance criteria for the linear model. The results indicated strong correlations for the 13-, 14-, 16-, and 22–23-month periods between the NAO index and precipitation values; and for the 13-, 14-, 16–17-, and 20–21-month periods between the IOD index and precipitation values. After cross-spectral analysis between the NAO and IOD indices and precipitation values, the maximum phase shift values increased as the periods increased, while the maximum phase shift value for each period was almost half of the period value. Moreover, the maximum cross-power spectral density (CPSD) values increased as the periods increased. High CPSD values were observed in the west of Turkey for the NAO and in the east of Turkey for the IOD.

Highlights

Precipitation is one of the most important components of the hydrological cycle; it affects other components such as flow, infiltration, and evaporation
This paper focuses on the effects of the different teleconnection patterns, namely the North Atlantic oscillation (NAO) and Indian Ocean dipole (IOD) indices, on precipitation in Turkey
239 different meteorology stations were considered, cross-spectral analysis were performed between the indices and precipitation values

Summary

Introduction

Precipitation is one of the most important components of the hydrological cycle; it affects other components such as flow, infiltration, and evaporation. Forecasting future precipitation behavior is important for planning agriculture or water resource management and in designing water structures. The winter and spring precipitation are cyclonic precipitation in Turkey which are more associated with the ocean oscillation. Summer precipitation is convectional and occur with the air rising during the day. Precipitation is highly variable both spatially and temporally in Turkey. Atmospheric physics and climatic processes are important for prediction of precipitation in Turkey. Short-term precipitation forecasting models such as European

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