The quasi 2-day wave (QTDW) at 82–97 km altitude over Collm
(51

The quasi 2-day wave (QTDW) is one of the most striking
dynamical features in the mesosphere and lower thermosphere. The QTDW was
first reported by

Regarding possible forcing mechanisms,

A hemispheric asymmetry has been observed

In the following we present analyses of the QTDW from a meteor radar (MR) at
Collm (51

A commercial VHF MR, distributed under the brand name SKiYMET

The meteor trail reflection heights vary between

The periods of the QTDW are obtained from Lomb–Scargle periodogram analyses
that are based on

Lomb–Scargle periodogram of the meridional wind for
a time interval of 11 days centered on 25 July 2010 (

To obtain amplitudes and phases of the QTDW a least-squares fit has been
applied to the zonal and meridional horizontal half-hourly winds, which
includes the prevailing wind, tidal oscillations of

The upper and lower panels of Fig.

Upper panel: total annual amplitudes between September

Periodograms of the meridional amplitude for the
years 2004–2014 at

The vertical zonal wind shear, which has been calculated from the difference
of the respective prevailing wind components at

Distribution of QTDW periods in summer (May–Aug) for the years

Generally, the meridional amplitude in Fig.

The lower panel of Fig.

The distribution of meridional amplitudes during the years

In each winter from

In the following we concentrate on the more intense summer QTDW, referring to
the months of May–August. In order to investigate the distribution of
periods with respect to the amplitudes, Fig.

In the following we show summer QTDW data for amplitudes of at least

The phase differences between zonal and meridional QTDW components at

Histogram of the

Histogram of the

Figure

Vertical wavelengths

Left panel: mean phase difference (black) between
zonal and meridional components for 2004–2014 and their standard deviations.
Right panel: zonal (red) and meridional (green) mean amplitudes for 2004–2014 and
their standard deviations. Amplitude difference with standard deviation in
blue. For both panels only dates with total amplitude

We apply superposed epoch analyses in two ways. First, the key events are
defined from the time series of the amplitude. Therefore, the time series is
filtered using a Lanczos low-pass filter with

Histogram of daily vertical wavelengths during
summer (May–August) for the time period from

A correlation of QTDW amplitudes to the

Superposed epoch analysis of vertical wind shear of the
zonal prevailing wind in blue and QTDW total amplitudes in red at

Seasonal mean QTDW total amplitudes for summer
(May–August, upper panel) and winter (November–February, lower panel, the
year refers to the one of the respective January) for different altitudes in
orange, green, blue and red. Error bars denote the standard error given by
the standard deviation of the

In summer, the amplitudes qualitatively show similar inter-annual variability
at each altitude with a major maximum in

In winter, amplitudes at different altitudes are not always as homogeneous as
in summer. However, there is a clear peak in all altitudes during winter
2005/2006 when a major stratospheric warming was observed. This is in good
agreement with the general view that enhanced planetary wave activity can
cause stratospheric warmings. The correlation between QTDW winter amplitudes
and solar radio flux in the lower height gates is slightly higher than in
summer but still not significant. Correlation coefficients vary between

As presented in the periodograms in Fig.

As a result, the estimates (2) and (3) behave very similar to the seasonal mean values concerning magnitudes and sign of the correlation coefficients for correlations with solar radio flux and vertical shear of the zonal wind.

Using the maximum as an estimate, the correlation with solar radio flux in
summer turns out to be slightly positive for most altitudes with

To conclude, differences obtained with the four methods are not very large. Thus, the obtained relation between QTDW amplitudes and wind shear is robust and independent from the chosen method.

The QTDW is analyzed from Collm VHF meteor radar data. The considered time
series begins after the installation of the radar in

On a

Phase differences between the zonal and meridional component turn out to be
slightly larger than 90

Vertical wavelengths were calculated from the vertical phase gradients. The
mode of a fitted lognormal distribution is

Furthermore, we find a connection between vertical zonal wind shear and QTDW
amplitudes by applying superposed epoch analyses. They show a maximum of
amplitudes about

Between QTDW amplitudes and the

We acknowledge the support from the German Research Foundation (DFG) and
Universität Leipzig within the program of open-access publishing. F10.7
solar radio flux data have been provided by NGDC through FTP access at