Dynamical Impacts of Stratospheric QBO on the Global Circulation up to the Lower Thermosphere

Abstract

One of the important features of the middle atmosphere dynamics is the quasi-biennial oscillation (QBO) of zonal mean flows at stratospheric heights (e.g., Baldwin et al., 2001;Holton & Tan, 1980). This phenomenon is observed at equatorial latitudes: the direction of the zonal wind changes to the opposite with the period varying between 22 and 34 months. The highest zonal wind velocities are observed at altitudes of 20-30 km: about 20 m/s for westerlies and about 30 m/s for easterlies (Baldwin et al., 2001). Although the QBO is a dynamic process occurring in the stratosphere in the vicinity of the equator, its influence in the form of a quasi-2-year periodicity is observed in the composition of the atmosphere and in hydrodynamic fields at other latitudes and altitudes. For instance, Holton and Tan (1980) analyzed the response of the extratropical circulation to the QBO and showed that it is particularly strong during northern winter, where the zonal mean westerly jet is weaker during the easterly QBO phase (eQBO) than that during the westerly QBO phase (wQBO). Garfinkel et al. ( 2012) concluded that the QBO effect at high latitudes might be related to the induced changes in the thermally balanced subtropical jet and in the associated changes in the refractive index, which restricts the propagation of transient Rossby waves into the subtropics enhancing transient wave activity and the meridional mass circulation. In addition, as it was shown by Cnossen and Lu (2011), QBO interacts with variations caused by the 11-year solar cycle. Gavrilov et al. (2015) studied peculiarities of planetary wave (PW) and orographic gravity wave (OGW) interactions in the middle and upper atmosphere under different QBO phases. They showed that transitions from eQBO to wQBO can cause PW amplitude changes up to ±(30-90)% at middle and high northern latitudes. According to Koval et al. (2018), variations of PW amplitudes may occur due to nonlinear interactions between PW modes and changes in the global circulation under different QBO phases, which produce changes in the refractivity indices and EP fluxes for PW modes. Recently, studies dedicated to the research of the influence of the QBO phases on the transport of greenhouse gases have become especially relevant (Gabriel, 2019). In particular, the numerical simulation was used to reveal the long-term changes in northern midwinter temperature, zonal wind, and residual circulation, that are much stronger during wQBO than during eQBO. Among the other important

Numerical simulation of stratospheric QBO impact on the planetary waves up to the thermosphere

“…The MUAM includes a parameterization of thermal and dynamical effects produced by mountain waves 32 and a spectrum of non-orographic gravity waves 33 . Numerous analyses have been carried out to validate MUAM, which have shown that it correctly reproduces the structure of the atmospheric circulation, PWs, and tides (e.g., 8,9,21,34,35 ), sudden stratospheric warmings 36 , as well as the resonance properties of the atmosphere (normal atmospheric modes) 20 .…”

“…This variability in model simulations is interpreted as interannual 20,21 . Physical and hydrodynamic processes taken into account in the current version of the MUAM and the scheme of a numerical experiment are described in 8 .…”

Моделирование Изменений Меридиональной Циркуляции Средней И Верхней Атмосферы В Переходные Фазы Кдк

“…Явление квазидвухлетнего колебания (КДК) экваториального зонального ветра является одной из важных особенностей динамики атмосферы [1]. Недавно на основе численного моделирования Коваль с соавторами [2] продемонстрировали, как изменения в структуре планетарных волн (ПВ) способствуют распространению эффектов КДК на полярные широты и в термосферу посредством модификаций потока Элиассена-Пальма (ЭП) и его дивергенции, и за счет образования вихревой меридиональной циркуляции.…”

“…Для определения фаз КДК используется разложение наблюдаемых вариаций зонального потока на эмпирические ортогональные функции (ЭОФ). Такой подход позволяет учитывать вертикальную эволюцию фаз КДК и минимизировать неопределенности в определении фаз КДК [2]. Всего было определено 4 фазы КДК: восточная фаза (вКДК), переходная с восточной фазы на западную (взКДК), западная (зКДК) и переходная от западной к восточной фазе (звКДК).…”

“…Всего было определено 4 фазы КДК: восточная фаза (вКДК), переходная с восточной фазы на западную (взКДК), западная (зКДК) и переходная от западной к восточной фазе (звКДК). Подробное описание особенностей задания фаз КДК в модели МСВА представлено в работе [2]. Для повышения статистической значимости моделирования для разных фаз КДК получены четыре серии (ансамбля), содержащих 10 расчетов модели.…”