Abstract. The 11-year solar cycle forcing is recognised as an important atmospheric
forcing; however, there remain uncertainties in characterising the effects of
solar variability on the atmosphere from observations and models. Here we
present the first detailed assessment of the atmospheric response to the
11-year solar cycle in the UM-UKCA (Unified Model coupled to the United Kingdom Chemistry and
Aerosol model) chemistry–climate model (CCM) using a three-member ensemble over the recent past (1966–2010). Comparison of the model
simulations is made with satellite observations and reanalysis datasets. The
UM-UKCA model produces a statistically significant response to the 11-year
solar cycle in stratospheric temperatures, ozone and zonal winds. However,
there are also differences in magnitude, spatial structure and timing of the
signals compared to observational and reanalysis estimates. This could be due
to deficiencies in the model performance, and so we include a critical
discussion of the model limitations, and/or uncertainties in the current
observational estimates of the solar cycle signals. Importantly, in contrast
to many previous studies of the solar cycle impacts, we pay particular
attention to the role of the chosen analysis method in UM-UKCA by comparing
the model composite and a multiple linear regression (MLR) results. We show that
the stratospheric solar responses diagnosed using both techniques largely
agree with each other within the associated uncertainties; however, the
results show that apparently different signals can be identified by the
methods in the troposphere and in the tropical lower stratosphere. Lastly, we
examine how internal atmospheric variability affects the detection of the
11-year solar responses in the model by comparing the results diagnosed from
the three individual ensemble members (as opposed to those diagnosed from the
full ensemble). We show overall agreement between the responses diagnosed for
the ensemble members in the tropical and mid-latitude
mid-stratosphere to lower mesosphere but larger apparent differences at Northern Hemisphere
(NH) high latitudes during the dynamically active season. Our UM-UKCA results
suggest the need for long data sets for confident detection of solar cycle
impacts in the atmosphere, as well as for more research on possible
interdependence of the solar cycle forcing with other atmospheric forcings
and processes (e.g. Quasi-Biennial Oscillation, QBO; El Niño–Southern
Oscillation, ENSO).
Supplementary material to "Simulating the atmospheric response to the 11-year solar cycle
forcing with the UM-UKCA model: the role of detection method and
natural variability"
