Comparison of NO(y) in different cores Don F. Smart and M. A. Shea sssrc@msn

1. Comparison of NO(y) in different cores Don F. Smart and M. A. Shea sssrc@msn.com The comparison of NO(y) data from different ice cores is fraught with difficulties. The cores are sampled by different methods with vastly different resolution. There are many sources of NO(y) ranging from Very large terrestrial sources, and Space sources (cosmic rays, auroral electrons and solar protons). There are also many transport processes, Terrestrial weather and deposition from the sea-air interface during storms, Poorly understood mesospheric and stratospheric transport processes. There seems to be no agreement of what is “high resolution”. For climate studies, bi-annual resolution is “high resolution”. For glaciochemistry studies, 6 to 10 samples/year is “high resolution”. For impulsive nitrate deposition, 20 to 30 samples/year is “high resolution”. There are significant uncertainties in the ice core dating procedures. There are seasonal and annual profiles, stratigraphy profiles, ion chemistry profiles, etc. For Summit, Greenland there is a consensus depth-date profile.

2. For the NO(y) studies, there are significant disagreements about the date of the NO(y) events. Dating discrepancies between the GISP2-H and BU summit short core are shown below.

3. We have attempted to determine the probable dating error by comparing the computed water content in the ice for each assigned annual date with the consensus GISP year-water content. For this comparison, we converted the ~400 samples/year BU data to the same number of samples each year in the GISP2-H core (a variable number ranging from 14 to 54). We used the snow density vs. snow depth profile (from the GISP2 home page), and the snow depth per year from each data set (both the BU short core and the GISP2-H core), to compute the water equivalent per-year for each data set. These were compared with the standard water content vs. depth for the GISP consensus and the significant discrepancies identified. One of the worst discrepancies is a computed 0.14 MWE for the GISP2-H core year of 1944 compared with a 0.30 MWE for standard water content.

4. There is a significant timing error in the 1943-1946 period. The computed water content is inconsistent by a factor of 2 resulting in a significant error. The Hekla volcano re-establishes the time sequence.

5. What resolution is necessary to find impulsive nitrate depositions? The nitrate data is “noisy” with climatological and metrological features controlling the deposition. There is a normal annual cycle of winter low – summer high that is apparent in “normal” conditions. There are occasional volcanic eruptions that provide absolute time markers. Seasonal Variation Summer High – Winter Low Volcanic Eruption

6. It is our thesis that the solar particle contribution to the total NO(y) deposition is a short, impulsive event of 4 to 6 weeks duration. The GISP2-H core was specifically obtained for high resolution studies and sampled every 1.5 cm. This resulted in 14 to 54 samples per year, depending on the precipitation. The BU “short core” was analyzed using the continuous flow method resulting in ~400 samples per year. Below we have re-plotted the BU short core result at resolution of 10 and 52 samples per year.

7. It is our opinion that sample rates of 10 or less samples per year are inadequate to resolve impulsive NO(y) enhancements form the normal variability inherent in the nitrate data. We suggest the weekly resolution (~52 samples per year) is necessary to clearly delineate impulsive NO(y) deposition events.