Research Projects


I am not actively seeking graduate students or post-docs as I have no funding to support them.
Below is a description of some of my current research interests.

Merged Ozone Data (MOD)

MOD web page


Total Ozone Data Table
V8.6 TOMS/SBUV Through July 2015

The SBUV and TOMS instruments have been measuring the total column and profile of ozone in the stratosphere since 1978. We have put together a Merged Ozone Data page to describe the intercalibration of instruements to form a merged time series of ozone. The paper [Stolarski and Frith, 2006] describing the first version of the data set can be found here. An updated paper [Frith, et al., 2014] describing the current MOD data set based on Version 8.6 SBUV measurements is found here. A more recent paper [Frith et al., 2017] on the vertical profile data set has recently been published in ACP.

Ozone Trends and Recovery

A central question for ozone trend research is whether ozone measurements show that the ozone layer is responding to the provisions of the Montreal Protocol. There are three categories of potential answers to this question:

1) The evidence demonstrates that ozone IS following the expectations from the provisions of the Montreal Protocol.
2) The evidence DOES NOT INDICATE one way or another whether ozone is following the expectations from the Montreal Protocol.
3) The evidence indicates that ozone IS NOT following the expectations from the Montreal Protocol.

Figures 1 and 2 show some qualititative evidence that ozone IS following the provisions of the Montreal Protocol. The chemical transport model (CTM) simulations of the total column ozone amount averaged between the latitudes of 60° south and 60° north are shown in red. The CTM simulations, made in 2005, were forced by time-dependent inputs of the concentrations of chlorine source gases, 11-year cyclic variations of solar ultraviolet radiation and time-varying aerosol surface area densities representing the El Chichón and Pinatubo volcanic eruptions. These model calculations were reported in Stolarski et al. [2006].

Note that the measurements generally follow the downward trend in total column amount of ozone with an 11-year solar cycle that is consistent with the model results. Closer inspection reveals that the measurements from the late 1970's to the early 1990's are somewhat below the model results, while the measurements from the early 1990's into the 2000's are about equal to the model results. In other words, this particular model computation indicated somewhat stronger downward trends than appeared in the measurements.



Figure 1: CTM projections of quasi-global (60°S-60°N) total column ozone made in 2005 (thick red line with range of seasonal variation indicated by red shaded area). Blue line indicates monthly measurements by SBUV series of satellites available at the time of the model computations.

In Figure 1 the measurements used for comparison to the model projection run from late 1978 to 2004 from Stolarski and Frith [2006]. These were the data available at the time of the publication of the model results by Stolarski et al. [2006]. Figure 2 shows the same model results with extended measurements described in Frith et al. [2014]. These measurements have been extended into 2017 as described on the Merged Ozone Data (MOD) web page. More information about the merged SBUV data set can be found above on this webpage.

The measurements appear to continue to qualitatively agree with the model project 12 years after that projection was made. The original model projection assumed a peak ultraviolet radiation for solar cycle 24 shortly after the year 2010 that was the same as that for the previous two cycles. The actual solar cycle 24 was significantly weaker as reflected in the ozone measurements of Figure 2.

The next step is to evaluate this qualitative agreement quantitatively. We will first evaluate the expected sensitivity to chlorine through a hierarchy of models. The first test will be to use 2D and 3D models to evaluate the expectation for latitude and altitude dependent trends.



Figure 2: CTM projections of quasi-global (60°S-60°N) total column ozone made in 2005 (thick red line with range of seasonal variation indicated by red shaded area). Blue line indicates monthly measurements by SBUV series of satellites updated into 2017.
To be continued

Figure 3: Trends in %/decade as a function of latitude and altitude computed for the time period from 2004 to 2017 from the results of a two-dimensional model forced with a time-dependent CFC scenario.

The Impact of Spectral Irradiance Variations on the Atmosphere and Climate: Model Simulations and Observations



Proposal Summary

This project started by examining the difference between the ozone response to solar variations due to two different renditions of the variation of solar ultraviolet radiation over a solar cycle. An important result was the realization that the response of ozone was very different for wavelengths less than 242 nm compared to wavelengths greater than 242 nm. Below 242 nm uv photolyzes both O2 and O3. The photolysis of O2 is dominant and leads to a positive response of ozone to the solar cycle. Above 242 nm uv photolyzes only O3 leading to a negative response of ozone to the solar cycle. The net response as a function of altitude depends on the relative variation of uv as a function of wavelength with the solar cycle. Our paper can be found here.