  We propose an approach for characterizing source-impact pathways, the
interactions of a set of variables in space-time due to an external forcing, in
climate models using in-situ analyses that circumvent computationally expensive
read/write operations. This approach makes use of a lightweight open-source
software library we developed known as CLDERA-Tools. We describe how
CLDERA-Tools is linked with the U.S. Department of Energy's Energy Exascale
Earth System Model (E3SM) in a minimally invasive way for in-situ extraction of
quantities of interested and associated statistics. Subsequently, these
quantities are used to represent source-impact pathways with time-dependent
directed acyclic graphs (DAGs). The utility of CLDERA-Tools is demonstrated by
using the data it extracts in-situ to compute a spatially resolved DAG from an
idealized configuration of the atmosphere with a parameterized representation
of a volcanic eruption known as HSW-V.
