Response of middle atmosphere to short‐term solar ultraviolet variations: 1. Observations

Abstract

A series of studies were performed concerning the response of low‐latitude ozone and temperature in the stratosphere and mesosphere to short‐term solar ultraviolet variability associated with the rotation of the sun. The studies are based on Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) stratospheric ozone and temperature data, Nimbus 7 solar backscattered ultraviolet (SBUV) stratospheric ozone and 205‐nm solar ultraviolet data, Solar Mesosphere Explorer (SME) 1.27‐μm mesospheric O3 data, SME 121.6‐nm solar ultraviolet data, and Nimbus 7 Stratosphere and Mesosphere Sounder (SAMS) stratospheric and mesospheric temperature data. Using a longer temperature time series than has been used in the past for such studies, response times of temperature to solar UV variability in the stratosphere are found to be unexpectedly long (6 days at 2 mbar) and to become much shorter in the mesosphere (1 day at 0.01 mbar). Maximum sensitivity of temperature to solar variability (0.3 K/percent 205‐nm radiation) is found to occur near 70 km. The coupling of the temperature and ozone response to solar UV variability has been isolated by studying ozone responses with and without temperature effects. Temperature effects tend to increase rather than decrease the amplitude and to shift the response time of stratospheric ozone to solar variability to an earlier time. Using a longer ozone time series than has been used in the past for such studies, the stratospheric ozone response with no correction for temperature effects is found to be approximately a 0.4% increase at 3 mbar for a 1.0% increase in 205‐nm solar radiation. In the mesosphere a major systematic ozone decrease has been detected near 0.05 mbar (∼70 km), with increased solar Lyman α (121.6 nm) radiation (−0.14% ozone decrease for a 1% increase in solar Lyman α). This may be caused by solar Lyman α photodissociating H2O vapor producing HOx, with subsequent destruction of Ox. Higher in the mesosphere, where H2O mixing ratios should be much lower, ozone is found to increase with increasing solar UV. Observed responses of HNO3 and NO2 to solar UV variability are also briefly discussed. The theoretical response of middle atmosphere species and temperature to solar UV variability is discussed in detail in a companion paper (Brasseur et al., this issue).

Solar signals in CMIP‐5 simulations: the ozone response

“…In addition, the model radiation codes, including methods for simulating heating from volcanic aerosols in the lower stratosphere, are described in detail in the references listed in Table 1. However, the modeled response of stratospheric ozone and 225 temperature to 11-yr SSI forcing depends strongly on the detailed treatment of the solar UV irradiance in the 120-300 nm spectral range. Experiments using a 1-D radiative-convective-chemical model presented by Shapiro et al (2013;see their km) have been confirmed observationally using satellite remote sensing measurements on the solar rotational (∼ 27-day) time scale (e.g., Hood 1986, Keating et al 1987, Hood et al 1991. The 245 absorption at the Lyman-α wavelength by O 2 is also responsible for a strong expected ozone increase in the upper mesosphere.…”

MIPAS Observations of Ozone in the Middle Atmosphere

“…The opposite occurs, 15 however, at 70 km (middle/left panel), with a tendency to decrease towards 2012. Observational evidence for a negative solar ozone response at these altitudes has been provided by the analysis of Solar Mesosphere Explorer (SME) data on solar rotation time scales (Keating et al, 1987). Our observations suggest a long-term decline rather than a solar cycle variation since no O 3 increase before the solar minimum in 2009 can be identified.…”

“…Observational evidence for a negative solar ozone response near 70 km has been provided by the Solar Mesosphere Explorer (Keating et al, 1987). MIPAS data suggest, however, more of a long-term decline than a solar cycle variation, although a clear attribution is not possible due to the relatively short observation period of MIPAS.…”

Sensitivity of the tropical stratospheric ozone response to the solar rotational cycle in observations and chemistry–climate model simulations

“…To focus on periodicities relevant to the solar rotational cycle (13.5 and 27 days), all the time series are now filtered using the digital filter that has been commonly used in previous solar rotational studies (e.g., Hood, 1986;Chandra, 1986;Keating et al, 1987;Hood and Zhou, 1998;Zhou et al, 2000). The filtering procedure consists of smoothing data with a 7-day running mean which removes short-term fluctuations.…”

“…A number of observational studies have been carried out to determine the effects of the solar rotational cycle on stratospheric ozone, generally at low latitudes (i.e., tropical region) based on the analysis of satellite observations (e.g., Hood, 1986;Eckman, 1986b;Keating et al, 1985Keating et al, , 1987Hood et al, 1991;Fleming et al, 1995;Zhou, 1998, 1999;Fioletov, 2009;Dikty et al, 2010). These studies have shown that the sensitivity of tropical ozone to the solar rotational cycle maximizes at about 40 km (or ∼ 3 hPa) and varies from 0.2 to 0.6 % for a 1 % change in solar UV radiation index, typically taken as the irradiance at the 205 nm wavelength.…”