HO_2 and OH, also known as HO_x, play an important role in controlling middle atmospheric O_3. Due to their photochemical production and short chemical lifetimes, HO_x are expected to respond rapidly to solar irradiance changes, resulting in O_3 variability. While OH solar cycle signals have been investigated, HO_2 studies have been limited by the lack of reliable observations. Here we present the first evidence of HO_2 variability during solar 27 day cycles by investigating the recently developed HO_2 data from the Aura Microwave Limb Sounder (MLS). We focus on 2012–2015, when solar variability is strong near the peak of Solar Cycle 24. The features of HO_2 variability, with the strongest signals at 0.01–0.068 hPa, correlate well with those of solar Lyman α. When continuous MLS OH observations are not available, the new HO_2 data could be a promising alternative for investigating HO_x variability and the corresponding impacts on O_3 and the climate

Li, King-Fai

Livesey, Nathaniel J.

Millán, Luis

Sander, Stanley P.

Santee, Michelle L.

Wang, Shuhui

Yung, Yuk L.

Zhang, Qiong

Caltech Authors - Main

 
 
1 
 
 
 
 
Geophysical Research Letters 
Supporting Information for 
Title First Evidence of Middle Atmospheric HO2 Response to 27-day Solar Cycles 
From Satellite Observations 
Shuhui Wanga, Qiong Zhangb, Luis Millána, King-Fai Lic, Yuk L. Yungb, Stanley P. 
Sandera, Nathaniel J. Liveseya, Michelle L. Santeea 
a Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 
b Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, 
USA 
c Department of Applied Mathematics, University of Washington, Seattle, WA, 98195, USA  
 
Contents of this file  
 
Figures S1 to S3 
Table S1  
 
Additional Supporting Information (Files uploaded separately) 
 
Captions for Dataset S1 
Introduction  
In the supporting materials, we include Figure S1 to show the cross correlation between 
the time series of MLS HO2 observations and solar Lyman-α at each pressure level 
shown in Figure 4. Figure S2 shows the 1-to-1 scatter plots and linear regression results 
for data shown Figure 4. The results in Figure S2 are summarized into a vertical profile 
plot in Figure 5 in the main manuscript.  
To compare our analysis results for data during 2012 – 2015 around the peak of Solar 
Cycle 24 (Figure 5), we also include Figure S3 here to show the analysis results for data 
during 2004 – 2005. Compared to results around the solar peak, the weaker correlations 
between HO2 variability and solar Lyman-α variability during 2004 – 2005 is consistent 
with the weaker solar activity during the declining phase of Solar Cycle 23.  
 
 
2 
 
To compare our analysis method with the band-pass filter method used in previous 
studies [Shapiro et al., 2012], we include Table S1 to show the linear correlation results 
from both methods. The latter generally produces larger correlation slopes but with 
larger error bars and weaker correlation coefficients, showing the advantages of our 
analysis method for this type of subtle signal extraction. 
The global mean offline HO2 data (55S-55N) during 2012-2015 that was used in this 
study is also included in the supporting materials as Dataset S1. The complete zonal 
mean offline HO2 data will be made publically available by the Aura MLS team in early 
2016. Anyone interested can register as a user at MLS’s website or contact the MLS 
team to get access to the data. 
 
 
 
Figure S1. Cross correlation between solar 27-day cycle variability signals in MLS HO2 
and solar Lyman-α at 6 pressure levels in the mesosphere. The time series plots of these 
scatter values are shown in Figure 4. HO2 is clearly shown to follow solar Lyman-α 
variability during the 27-day cycles with no time lag. 
 
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.010hPa
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.015hPa
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.022hPa
co
rre
la
tio
n 
co
ef
fic
ie
nt
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.032hPa
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.046hPa
time lag (days)
−30 −20 −10 0 10 20 30
−0.6
−0.3
0
0.3
0.6
level pressure = 0.068hPa
time lag (days)
 
 
3 
 
 
Figure S2. Linear correlation between solar 27-day cycle variability signals in MLS HO2 
and solar Lyman-α at 6 pressure levels in the mesosphere. The time series plots of these 
scatter values are shown in Figure 4. The liner fit slopes, fit uncertainties, and correlation 
coefficients R2 are summarized in Table S1 and illustrated in Figure 5.  
 
 
 
4 
 
 
Figure S3. Vertical profile of the magnitude of the MLS HO2 response to solar Lyman-α 
variability for the data during September 1, 2004 – December 31, 2005. The x-value is 
the slope of the linear fit between HO2 variability and Lyman-α variability. Error bars 
represent the uncertainty in the linear fit. The correlation coefficient R2 is plotted in blue 
and also reflected in the size of the symbols. The correlations are clearly weaker than 
those in Figure 5 for data during 2012 –2015. 
 
Pressure	  
(hPa)	  
Our	  analysis	   Band-­‐pass	  filter	  
Slope	   R2	   Slope	   R2	  
0.01	   0.43±0.04	   0.11	   0.48±0.04	   0.14	  
0.015	   0.38±0.02	   0.19	   0.42±0.03	   0.16	  
0.022	   0.44±0.02	   0.35	   0.46±0.03	   0.21	  
0.032	   0.48±0.02	   0.44	   0.52±0.03	   0.24	  
0.046	   0.46±0.02	   0.40	   0.50±0.03	   0.23	  
0.068	   0.32±0.02	   0.16	   0.30±0.03	   0.12	  
Table S1. Summary of the linear correlations (slopes with fit uncertainties, and 
correlation coefficients R2) between extracted HO2 variability and Lyman-α variability.  
“Our analysis” method is described in this manuscript and the results are shown in 
Figures S1 and 5. “Band-pass filter” method refers to the 20-35day filter used in Shapiro 
et al., [2012].  
Data Set S1. MLS global mean HO2 data used in this study. Number density data during 
2012-2015 at 6 pressure levels in the mesosphere is included in the data file. 
 


English

First evidence of middle atmospheric HO_2 response to 27 day solar cycles from satellite observations

https://authors.library.caltech.edu/63339/2/grl53616-sup-0001-s04.pdf

First evidence of middle atmospheric HO_2 response to 27 day solar cycles from satellite observations

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