The goal of this project is to evaluate the possibility that WPBR was spread from the Sierra Nevada to the Sacramento Mountains of south-central New Mexico by a discrete atmospheric transport event.  The three sites near Cloudcroft, New Mexico, where the evidence of the earliest infection is present are all located on the windward side of the mountains at about 2440m (Van Arsdel, et al. 1998).  The earliest infections are estimated to have occurred around 1970.  This study will examine April through June of the years 1965 to 1972 for possible transport events.

The investigation will proceed in the following manner:
    1. Identification of all improbable days:
        a. Days with precipitation at the source or the target
        b. Days with unfavorable upper level flow
        c. Days with unfavorable surface flow
    2. Detailed evaluation of the probable days:
        a. Addition of spore viability factors at the source
        b. Identification of days with fog or clouds at 2440m on the windward side of the Sacramento Mountains
        c. Possible development of a synoptic index accounting for surface and upper level conditions in the region
    3. List of the most probable periods for long distance atmospheric transport with a rating of all probable days.

The first stage of this study is to identify all of the days deemed highly improbable for transport.  First, days with precipitation at either the target or the source were identified as improbable for long distance transport.  Precipitation at Bakersfield, California, (near the source of the spores) would wash spores out of the air, making them unavailable for long distance atmospheric transport.  The uniform elevation of the earliest infection sites at the target, near Cloudcroft, New Mexico, indicates that the spores could not have arrived with a rainfall event that would have spread the spores evenly at all elevations with the falling rain.  The spores more likely arrived with a fog or low cloud deck at 2440m.  Second, days with atmospheric flow at the 500mb level that would preclude transport were considered improbable for long distance transport.  Days when either the target or the source were out of the zone of baroclinicity or when meridional flow was dominant in the region were included in this group.  Finally, days with surface winds that were unfavorable for long distance transport were included in the group of improbable days.  Surface winds that were predominantly easterly, as is the case when a high pressure system is located to the north and west of the region, or when surface flow was weak are examples of these days.

Some weather maps for the period in question are not available to the research team at this time.  These maps are on order from National Oceanic and Atmospheric Administration (NOAA), and upon the receipt of these maps the identification of all days when transport was improbable will culminate.  Of the 728 days in the 8-year study period, in the months April through June, 133 maps are missing from the archive available to the research team.  The remaining 595 days have been evaluated:
        · 36 days were eliminated based on precipitation at Bakersfield, California
        · 70 additional days were eliminated based on precipitation at Cloudcroft, New Mexico
        · 394 more days were eliminated based on unfavorable upper air or surface flow
Ninety-five probable days, 16% of the sample, remain to be investigated.  Fifty-two (55%) of these probable days are in April, 28 (29%) are in May and only 15 (16%) are in June.

The resultant list of possible days for transport will be evaluated further to rate the probability of transport on each of the probable days.  First, environmental factors affecting spore viability at the source will be considered.  These factors include solar radiation levels and atmospheric humidity.  Second, an attempt will be made to identify conditions that lead to fog or low level cloud formation on the windward side of the Sacramento Mountains.  Cloud cover data for Cloudcroft, New Mexico, are not available from the National Climatic Data Center (NCDC) archive of cooperative weather station data.  Further inquiries to other databases continue in the effort to obtain cloud cover information for the site.  Because it is likely that the spores arrived at the target area on a fog or cloud deck at 2440m, cloud cover information will facilitate identification of conditions when the spores were likely to reach the source region.  Finally, a synoptic index may be developed to encompass the surface and upper level conditions at both the target and the source.  This index will enable the research team to rank days by probability of transport based on multiple variables.  This list of probable days with probability ratings will be the final product of this project.

References:

Van Arsdel, E. P., D. A. Conklin, J. P. Popp, and B. W. Geils.  1998. The distribution of white pine blister rust in the Sacramento Mountains of New Mexico.  Proc. First IUFRO Rusts of Forest Trees WP Conf., 2-7 Aug 1998. Saanelka, Finland: Finnish Forest Research Institute. Research Papers 712:275-283.