WRRCTMR No.77 Spectral Analysis of Hawai'i Rainfall

Abstract

The empirical orthogonal function was applied to analyze 40-yr annual rainfall data for 80 stations in the state of Hawaii, which included 21 stations on Hawaii, 18 on Maui, 5 on Molokai, 5 on Lanai, 16 on Oahu, and 15 on Kauai. The chi-square statistic was introduced to test the stabilities of eigenvectors, E-1, E-2, and E-3, for the state and its six major islands. The eigenvectors, especially E-1 and E-2, for the state and individual islands are quite stable within the 30-yr period. Eigenvectors within the 30-yr period with 5-yr data change are more stable than those within a 30-yr period with 10-yr data change. The 40-yr eigenvectors are even more stable than those in the 30-yr period. Both the maximum and conventional power spectral analyses were used to analyze the time-dependent coefficients of E-l, E-2, and E-3. The quasi-biennial oscillation (2-yr cycle) is the predominant cycle for the state and for Maui and Oahu. The El Nino cycle (4- to 4.4-yr cycle) exists in the state and the islands of Hawaii and Kauai, and the 3- to 3.3-yr cycle on Kauai. No significant sunspot cycle (11- and 22-yr cycle) was found on Hawaii.