Author: Emily Berndt
Here at SPoRT we’ve been comparing the RGB Air Mass Imagery with the AIRS Total Column Ozone product to confirm regions of stratospheric air on the RGB Air Mass Imagery. The presence of stratospheric air can identify regions susceptible to tropopause folding. Identifying these regions can aid in forecasting cyclogenesis and non-convective winds as well as the promotion or suppression of convection. Recall that stratospheric air shows up as red/orange on the RGB Air Mass Imagery. The MODIS image from 1027 UTC this morning highlights the low pressure system off the Pacific Coast. Notice the red coloring collocated with the system (purple circle). We shouldn’t jump right to the conclusion that stratospheric air is present because limb cooling can cause a false influence of red and blue coloring on the edge of the swath.
When we look at the AIRS Total Column Ozone product from 1000 UTC, there are high ozone values in this same region (purple circle). So yes we see red coloring on the RGB Air Mass Image and high values of ozone present, but how do we know whether these high ozone values are ozone-rich stratospheric air or are normal values for that region and time of year?
Thus far we haven’t found a magic number or threshold of ozone concentration that represents stratospheric air more clearly. So our new Ozone Anomaly product can answer the question of whether there is a significant enough deviation from climatology to consider high ozone regions as stratospheric air.
Two literature references have provided the information to create an Ozone Anomaly product. Van Haver et al. (1996) states stratospheric air is characteristic of ozone values that are 25% greater than climatology. Ziemke et al. (2011) constructed a global stratospheric ozone climatology using the Ozone Mapping Instrument and Microwave Limb Sounder integrated ozone profiles. The Ozone Anomaly product is derived by calculating the percent of normal (climatology) on a scale from 0-200 percent. Interpretation of percent of normal is very easy: values at 100% equal climatology, less than 100% are below climatology, and above 100% are greater than climatology. We’ve constructed the color table so that values 125% and great are blue. One can quickly look at the image and see regions that meet the criteria for stratospheric air. Now compare all three products, we see red on the RGB Air Mass Image, high ozone values on the Total Column Ozone product, and the Ozone Anomaly product establishes the high ozone values do indeed represent stratospheric air.
Van Haver, P. and Coauthors, 1996: Climatology of tropopause folds at midlatitudes. Geophys. Res. Lett., 23, 1033-1036.
Ziemke J. R., S. Chandra, G. J. Labow, P. K. Bhartia, L. Froidevaux, J. C. Witte, 2011: A global climatology of tropospheric and stratospheric ozone derived from Aura OMI and MLS measurements. Atmospheric Chemistry and Physics, 11, 9237-9251.