What Drives Negative KDP above the Melting Layer? The Hidden Role of Secondary Ice Production

<jats:p> Secondary ice production (SIP) remains a major uncertainty in understanding deep convection because its rates and controlling conditions are poorly constrained. Using the Tracking Aerosol Convection Interactions Experiment (TRACER) C-band and operational S-band radar observations, Houston Lightning Mapping Array (HLMA) lightning data, and large-eddy simulations (LESs), this study investigates negative <jats:italic toggle="yes">K</jats:italic> <jats:sub>DP</jats:sub> observed above the melting layer as a potential signature of SIP and storm electrification. Among 413 observed deep convective cells, 238 cases (~57.6%) exhibit negative <jats:italic toggle="yes">K</jats:italic> <jats:sub>DP</jats:sub> above the melting layer, and 49 of 123 lightning-active cases (~39.8%) show negative <jats:italic toggle="yes">K</jats:italic> <jats:sub>DP</jats:sub> near HLMA sources. These observations suggest that negative <jats:italic toggle="yes">K</jats:italic> <jats:sub>DP</jats:sub> is associated with small, vertically oriented, electrically aligned ice particles. LESs with spectral bin microphysics reproduce negative <jats:italic toggle="yes">K</jats:italic> <jats:sub>DP</jats:sub> with high likelihood only when SIP is included, especially fragmentation of freezing drops, which increases ice water path, decreases liquid water path, and reduces accumulated precipitation by ~7.6% in the examined case. </jats:p>