Kuantifikasi osilasi kuasi dua tahunan stratosfer (QBO) menggunakan data ECMWF-interim reanalysis

Abstract

Data ERA-Interim dengan periode 30 tahun (Januari 1981 – Desember 2010) keluaran ECMWF (European Center for Medium-Range Weather Forecasts) digunakan untuk menganalisis secara kuantitatif karakteristik QBO (quasi-biennial oscillation). Analisis pada penelitian ini menunjukkan bahwa fasa timuran dan baratan QBO merambat bergantian dengan periode ~27.7 bulan, yang secara garis besar periodenya lebih pendek dari 28.4 bulan hasil perhitungan Baldwin et al. (2001; observasi) dan 28.2 bulan hasil perhitungan Pascoe et al. (2005; ERA-40). Berdasarkan metode EQA (Equivalent QBO Amplitude), kami menemukan bahwa amplitudo maksimum dari kecepatan rata-rata angin zonal terhadap bujur (U), rata-rata zonal dari suhu (T), pergeseran vertikal angin zonal (du/dz), dan laju perubahan vertikal pergeseran vertikal angin zonal (d2u/dz2) secara berturut-turut adalah ~28.3 m/s, ~3.4 K, ~4.8 m/s/km, dan ~1.0 m/s/km2. Amplitudo tersebut berkurang secara eksponensial mengikuti distribusi Gaussian terhadap lintang. Struktur twofold dari QBO merambat ke bawah dengan laju ~1 km/bulan. Kami juga menemukan bahwa hubungan QBO-du/dz dengan QBO-T memenuhi persamaan angin termal, karena sangat kecilnya kontribusi dari rata-rata pergerakan angin vertikal dan meridional. Selain itu, konsentrasi dari total column ozone (TCO) di daerah tropis secara signifikan dipengaruhi oleh QBO. Selama fasa baratan QBO konsentrasi TCO secara relatif meningkat di wilayah stratosfer-bawah, namun menurun selama fasa timuran.

A 30-year ERA-Interim data from the European Center for Medium-Range Weather Forecasts (ECMWF) was used to quantitatively analyze the characteristics of the quasi-biennial oscillation (QBO). The analysis of this research showed that the zonally symmetric easterly and westerly phase of QBO regimes alternate with period of ~27.7 months, being marginally shorter than ~28.4 and ~28.2 months as measured by Baldwind et al. (2001; observation) and Pascoe et al. (2005; ERA-40) respectively. Based on Equivalent QBO Amplitude (EQA) method, we found that the maximum amplitudes in zonal mean zonal wind (u), temperature (T), vertical shear (du/dz) and quadratic vertical shear (d2u/dz2) are ~28.3 m/s , ~3.4 K, ~4.8 m/s/km, and ~1.0 m/s/km2 respectively. The amplitudes decay exponentially with a Gaussian distribution in latitude. The twofold-structure of QBO descends downward at rate of ~1 km/month. We also showed that QBO-du/dz and QBO-T satisfy the thermal wind balance relation due to very small contribution of the mean meridional and vertical motion. Moreover, we found that the concentration of the total column ozone (TCO) in the tropics is significantly influenced by QBO. During the westerly phase of QBO, the TOC is relatively increased in the lower-stratosphere, but decreased during the opposite phase. Keywords: QBO, amplitudes, thermal wind balance, total column ozone (TCO).