An Objective Method for Fog Classification: An Isotope Approach.

Abstract:

Although fog is an important component of the hydrological cycle in dryland environments, its formation mechanisms are not fully understood, leading to misclassification of fog types. This misclassification based on subjective methods may result in under or over estimation of the potential impacts of global climate change on the ecohydrology of fog dependent ecosystems. To fill this knowledge gap, this study applies stable isotopes to classify fog objectively and compares this classification to meteorological conditions defined for the formation of these different fog types. Preliminary results suggest that this isotope based fog classification is consistent with expected meteorological conditions for each fog type. For example, average wind speed decreased from advective, mixed and radiation fog while estimated fog (cloud) height (LCL) was lowest during radiation fog and highest during advective fog. Radiation fog isotopes were inversely related to LCL highlighting the importance of local meteorological conditions to radiation fog condensation. In addition, the positive lc-excess values for advective and mixed fog suggested moisture was sourced elsewhere (Atlantic Ocean) while the almost neutral (0) value for radiation fog indicated local moisture sources. While visual classification methods may suggest one type of fog over an area, this isotope based method suggests multiple types as well as an evolution of fog type across the landscape. This study provides an objective classification method for fog classification which will enable more accurate assessments of the threat of climate change on fog dependent ecosystems.