# Presentation: 171289

## PV-Theta Mapping of AURA MLS Profile Data A. Bender1, S. Frith2, G. Morris1, D. Lary3

*1** Dept. of Physics & Astronomy, Valparaiso University, Valparaiso, IN*
*2** SSAI, NASA Goddard Space Flight Center, Greenbelt, MD*
*3** GEST, University of Maryland Baltimore County, Baltimore, MD*

**Introduction**
- Mapping quasi-conserved atmospheric constituents, such as lower stratospheric ozone, into potential vorticity (PV) - potential temperature (Theta) coordinates is a common technique used to analyze sparse data sets.  Ozone transformed into a flow-following dynamical coordinate system is insensitive to meteorological variability.  Therefore data from a wide range of times and locations can be compared, so long as the measurements were taken in the same air mass, as defined by the PV.  The mapping approach assumes a high correlation between the ozone and PV fields.  In this study, we use the comparatively high resolution of the MLS data to test the correlation between ozone and PV in the lower stratosphere.  We evaluate the ability of the PV mapping technique to reproduce the MLS profile data by comparing reconstructed data to the original data as a function of latitude, altitude, and season.  We use dynamical data from the NCEP assimilation to represent the PV and Theta fields.

**Latitude Gradient Within PV Bins**
- Ozone values are graphed as a function of latitude in each PV bin. If the ozone values within a PV bin are further sorted by latitude, a latitude dependent ozone gradient is sometimes observed. This observation suggests that both latitude and PV are required to characterize the ozone in these cases.

- September 11 - 15, 2006
- AURA Science Team Meeting

**The PV-Theta Mapping Technique**
- Due to the conservation of PV and Theta along the path of an air parcel, an ozone mapping in PV-Theta space produces a climatology with greater accuracy than a simple zonal average.  While this increased reliability is often achieved for steep gradients in PV, areas with little change in the PV field can be adversely affected by this technique.  As a first step in evaluating the reliability of the PV-Theta technique, we examine the correlation coefficients of ozone and PV as a function of latitude, Theta, and season.

**Conclusions**
- Based on these observations, it is clear that a PV-Theta mapping does not guarantee a more accurate ozone climatology than a zonal average.  While the technique works well in most areas with high PV gradients, other regions show little correlation between the ozone and PV field.  It is advisable to be cautious in these cases, as a PV-Theta mapping can potentially create artificial features in the ozone map.

**References**

**Technique Comparison **

- Fig. 3  This figure shows the average of ozone sorted by latitude in each 1-PVU bin and the overall mean of the ozone data as a function of PV.  Bins with a large variance in the ozone values as a function of latitude are problematic when relying only on PV information to sort and average the ozone measurements.  This problem is found particularly at low latitudes in the winter hemisphere.

- Fig. 1  These plots show the correlation coefficient as a function of Theta between MLS ozone and Latitude (red) and MLS ozone and modified potential vorticity (MPV, blue) in seven broad latitude bands.
- In January we note the relatively strong correlations between ozone and MPV at higher winter latitudes, with weak correlations elsewhere. In most latitude bands at most Theta levels, the correlation with MPV is at least as good as that with latitude.  However, the correlation with MPV is less frequently than 0.7 (i.e., MPV explains less than 50% of the ozone variability).

- Fig. 2  This plot demonstrates the reliability of PV in conveying the January ozone field.  In each region, the average ozone correlation with PV is displayed.  Regions at high northern latitudes correlate well with PV.  Regions with small PV gradients, however, are not well correlated, as can be seen in the tropics and in the summer hemisphere.

*Note:  *
*January data dominates this presentation as it provides a fairly consistent illustration of the technique.  More detailed graphical analysis of the entire year can be found at *_[http://hyperion.](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[gsfc](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[.nasa.gov/People/](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[Frith](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[/](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[webdir](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)__[/PVI/Aura_PVI.html](http://hyperion.gsfc.nasa.gov/People/Frith/webdir/PVI/Aura_PVI.html)_

- Lait, L.R.: An Alternative form of potential vorticity, *J. Atmos. Sci., 51*,12,1754-1759, 1994.
- Lait, L.R., M.R. Schoeberl, P.A. Newman, et. Al.: Ozone loss from quasi-conservative coordinate mapping during the 1999-2000 SOLVE/THESEO 2000 2000 campaigns, *J. Geophys. Res., 107*, art.no. 8274, 2002.
- Lait, L.R., M.R. Schoberl, P.A. Newman, et al.: Reconstruction of O-3 and N20 fields from ER-2, DC-8, and balloon observations, *Geophys. Res. Lett., 17*, 521-524, 1990.
- McIntyre, M.E.: Towards a Lagrangian-mean description of stratospheric circulations and chemical transports*, Philos. T. Roy. Soc. A., 296*, 129-148, 1980.
- Schoeberl, M.R., and L.R. Lait: Conservative-coordinate transformations for atmospheric measurements, in *Proceedings of the International School of Physics:  The Use of EOS for Studies of Atmospheric Physics*, Elsevier Science, New York, 1992.
- Schoeberl, M.R., L.R. Lait, P.A. Newman, et al.: Reconstruction of the constituent distribution and trends in the Antarctic polar vortex from ER-2 flight observations, *J. Geophys. Res., 94*, 16,815-16,845, 1989.
- Waters, et al., The Earth Observing System Microwave Limb Sounder (EOS MLS) on the Aura Satellite, *IEEE Trans. Geos. Rem. Sens., 44*, 1075 - 1092, 2006.

- Fig. 4  At right, we examine the reconstructed ozone values based on PV-Theta climatologies both with and without the additional latitude fit. Apparent in these plots is the problematic region in the lower latitudes of the winter hemisphere.  The latitude fit improves the reconstruction by approximately 10% in the these areas.  The fit also reduces the standard deviations of the differences.

- Fig. 5  When the latitude of the measurement is taken into account, the bias is reduced below 5% in most regions of the globe (Left). The fit to latitude is capturing, most, but not all the latitude-dependent variability in the bin. The actual cause of the variability is likely a combination of factors that vary in the same way as the latitude gradient in ozone.

- The following charts summarize the regions and seasons in which PV-Theta mapping works well and works poorly.

- The following criteria were used to determine the colors for the above plots:
- -Red:  		Bias > 5% or standard deviation greater using PV than zonal mean.
- -Yellow:  	PV mapping does not cause bias but does not improve standard deviation			 over the simple zonal mean.
- -Green:  	Bias < 5% and at least 20% decrease in standard deviation

- Funding provided by:
- NASA Earth-Sun System Division
- The Indiana Space Grant Consortium