AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Influence of Storm Origin and Type on Biological Ice Nucleation Activity in Louisiana Precipitation
RACHEL JOYCE, Heather Lavender, Jennifer Farrar, Mickaël Vaitilingom, Juliana D'Andrilli, Brent Christner, Louisiana State University
Abstract Number: 144 Working Group: Bioaerosols
Abstract Certain microorganisms are ice nucleation active and initiate ice formation at temperatures much warmer than most mineral dust particles in the atmosphere. As such, these bioaerosols may significantly contribute to precipitation formation processes at mid tropospheric altitudes. To better characterize biological ice nuclei (IN) in the atmosphere, we collected and analyzed samples from 54 precipitation events in Louisiana from May 2013 to March 2015. Biological IN activity of the samples was measured between -4°C and -15°C using an immersion freezing assay, and microbial cell abundance was quantified using epifluorescence microscopy. Major ion (NO$_3$^-, SO$_4$^(2-), Cl$^-, Na$^+) and dissolved organic carbon (DOC) concentrations, pH, and conductivity of collected precipitation were also measured. Storm origin and classification was determined by examining NEXRAD reflectivity, GOES-East satellite imagery, NOAA’s HYSPLIT trajectories and WPC surface analyses. Biological IN concentrations at -15°C ranged from 52 to 12,000 IN L$^(-1) of precipitation, with cell concentrations remaining relatively constant at ~10$^4 to ~10$^5 cells L$^(-1) of precipitation and independent of IN activity. Analysis of 72-hr backwards trajectories indicated air masses at 5000, 6000, and 8000 mAGL that originated over the tropical Pacific ocean correlated strongly with high biological IN activity (MANOVA, p = 0.0355, p = 0.0067, and p = 0.0208, respectively), when compared to other North American air masses. Additionally, precipitation from frontal nimbostratus storms contained significantly higher biological IN activity than that of convective storms (MANOVA, p = 0.0141), with snow and sleet from nimbostratus clouds yielding the highest detected biological IN activity (MANOVA, p < 0.001). Concentrations of Cl$^-, Na$^+, NO$_3$^- and pH showed moderate correlations with biological IN active between -6°C and -9°C. Collectively, our data suggest that variation of biological IN activity in precipitation is connected to air mass origin, storm type, and precipitation type.