Stable isotope constraints on the vertical exchange of moisture in the convective boundary 
layer
Adriana Bailey


Climate models broadly fail to capture the dynamics that underlie the exchange of
moisture, energy, trace gases, and other materials between the boundary layer and the
atmosphere above. This weakness motivates the development of new observational
techniques that elucidate vertical transport processes. Because stable isotope ratios in
water record the hydrological history of air masses, they effectively trace moisture
transport in the vertical and the water cycle-processing of climatically important
atmospheric constituents like aerosol. Measurements of the 18O/16O isotope ratio from
Hawai’i are used 1) to distinguish moisture transport mechanisms and their effects on
aerosol within the subtropical mixed layer and 2) to investigate assumptions about the
sensitivity of entrainment-mixing near the top of the convective boundary layer (CBL) to
large-scale free tropospheric dynamics. Though air at the top of the CBL may be as dry
as free tropospheric air observed near the Big Island’s summit (4200 m), its isotopic
composition suggests more recent contact with mixed layer moisture. The possibility that
the humidity characteristics of this air mass are set by strong vertical mixing events that 
punctuate periods of weak mixing is examined. Furthermore, since convective mixing events 
appear related to large-scale dynamical conditions, two and a half years of isotope ratio 
observations from the Mauna Loa Observatory (3400 m) are correlated with atmospheric 
circulation patterns on synoptic timescales and longer. Preliminary results from the time 
series analysis are discussed.