On the detection of the solar signal in the tropical stratosphere

Abstract

Abstract. We investigate the relative role of volcanic eruptions, El Niño-Southern Oscillation (ENSO), and the quasibiennial oscillation (QBO) in the quasi-decadal signal in the tropical stratosphere with regard to temperature and ozone commonly attributed to the 11 yr solar cycle. For this purpose, we perform transient simulations with the Whole Atmosphere Community Climate Model forced from 1960 to 2004 with an 11 yr solar cycle in irradiance and different combinations of other forcings. An improved multiple linear regression technique is used to diagnose the 11 yr solar signal in the simulations. One set of simulations includes all observed forcings, and is thereby aimed at closely reproducing observations. Three idealized sets exclude ENSO variability, volcanic aerosol forcing, and QBO in tropical stratospheric winds, respectively. Differences in the derived solar response in the tropical stratosphere in the four sets quantify the impact of ENSO, volcanic events and the QBO in attributing quasi-decadal changes to the solar cycle in the model simulations. The novel regression approach shows that most of the apparent solar-induced lower-stratospheric temperature and ozone increase diagnosed in the simulations with all observed forcings is due to two major volcanic eruptions (i.e., El Chichón in 1982 and Mt. Pinatubo in 1991). This is caused by the alignment of these eruptions with periods of high solar activity. While it is feasible to detect a robust solar signal in the middle and upper tropical stratosphere, this is not the case in the tropical lower stratosphere, at least in a 45 yr simulation. The present results suggest that in the tropical lower stratosphere, the portion of decadal variability that can be unambiguously linked to the solar cycle may be smaller than previously thought.

The 11-year solar cycle in current reanalyses: a (non)linear attribution study of the middle atmosphere

“…However, the results presented by Chiodo et al (2014) suggest the contribution of SC variability could be smaller since two major volcanic eruptions are aligned with solar maximum periods and also given the shortness of the analysed time series (in our case, 35 years). These concerns related to the lower stratospheric response of ozone and temperature derived from observations have already been raised (e.g.…”

Trends of ozone total columns and vertical distribution from FTIR observations at eight NDACC stations around the globe

“…9) while values of 1 % have been reported (Sioris et al, 2014) at about 25 km. However, the recent work of Chiodo et al (2014) shows that the apparent solar cycle signal in the tropical lower stratosphere for the period 1960-2004 is due to the two volcanic eruptions of El Chichón in 1982 and Mt. Pinatubo in 1991, and the authors find robust solar cycle signals only in the middle and upper stratosphere.…”

“…At Wollongong, the 2.5 % ozone response to solar cycle in the upper layer is in agreement with previous studies, but the response in the middle stratosphere (∼ 6 %) is much larger than previously reported (∼ 1 %). The 11-year solar cycle effect is still subject of debate (WMO, 2010;Chiodo et al, 2014), so that an additional decade of measurements would help in fixing its real impact on ozone. This is particularly true for our shortest time series of Lauder, Izaña and Thule.…”

Reconciling differences in stratospheric ozone composites

“…This is often performed using MLR (WMO/UNEP, 1994; Soukharev and Hood, 2006;Chiodo et al, 2014;Kuchar et al, 2015;Harris et al, 2015). However, the use of DLM, first applied to ozone data by Laine et al (2014), appears to be more robust at estimating the background trend, especially if it is nonlinear.…”