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

Abstract

With the help of numerical simulation, a detailed analysis of the dynamical effect of the stratospheric quasi-biennial oscillation (QBO) of the equatorial zonal wind on the planetary waves (PWs) up to thermospheric heights is carried out for the first time. The 3-dimensional nonlinear mechanistic model of middle and upper atmosphere (MUAM) is used, which is capable of simulating the general atmospheric circulation from the surface up to 300-400 km altitude. The amplitudes of stationary and westward travelling PWs with periods from 4 to 10 days are calculated based on ensembles of model simulations for conditions corresponding to the easterly and westerly QBO phases. Fluxes of wave activity and refractive indices of the atmosphere are calculated to analyze the detailed behavior of the PWs. The important result to emerge is that the stratospheric QBO causes statistically significant changes in the amplitudes of individual wave components up to 25% in the mesosphere-lower thermosphere and 10% changes above 200 km. This change in wave structures should be especially noticeable in the atmosphere during periods of low solar activity, when the direct contribution of solar activity fluctuations is minimized. Propagating from the troposphere to the upper atmosphere, PWs contribute to the propagation of the QBO signal not only from the equatorial region to extratropical latitudes, but also from the stratosphere to the thermosphere. The need for a detailed analysis of large-scale wave disturbances in the upper atmosphere and their relationship with the underlying layers is due, in particular, to their significant impact on satellite navigation and communication systems, which is caused by amplitude and phase fluctuations of the radio signal.

Figure 1

Latitude-height distributions (shaded) of the zonal-mean wind (m/s, a), according to MUAM ensemble for January–February, eQBO; respective zonal mean wind increments due to change from wQBO to eQBO (b); vertical profiles of the equatorial zonal wind for both QBO phases (c). Contours in the panels (a, b) reveal EP-flux divergence and its increments in 10^–2 m²/s²/day, respectively.

Figure 2

Amplitudes of the geopotential height variations caused by SPW1 and SPW2 in gp. m. (a and b, left, respectively) for the MUAM ensemble for January–February, eQBO; respective amplitude increments due to change from wQBO to eQBO (right). Arrows show EP flux (left) and its increments (right) in e^z/70 m²/s² (vertical component is multiplied by 200). Gray background shows waveguide (left) and 95% statistical significance (right). Intervals between contours are indicated in the left bottom corner of each plot.

Figure 3

The same as Fig. 2 but for the westward travelling atmospheric NMs: τ = 4 days, m = 2 (a); τ = 5 days, m = 1 (b).

Figure 4

The same as Fig. 2 but for the westward travelling atmospheric NMs: τ = 7 days, m = 2 (a); τ = 10 days, m = 1 (b).

Figure 5

Vertical profile of the sum of all terms in the perturbed potential enstrophy balance equation for non-migrating diurnal tide (averaged over latitudes and longitudes, PVU²/day)—(a). Sum of terms describing nonlinear interaction between SPW1 and migrating diurnal tide—(b).