Moisture Variability and Nocturnal Convection David B. Parsons, Crystal Pettet, and Tammy Weckwerth NCAR/ATD Acknowledgements to Ed Browell et al., Cyrille Flamant et al., and Steve Koch and the bore folks

Sounding-based Schematic of Nocturnal Convection Initiation From Trier and Parsons 1993

Moisture Upstream of MCS Inflow 2nd LLJ Deeper Mixed Layer from near the dryline LLJ

Nocturnal MCS June 6th 2 ~Frontal Position 3 1 ~DC-8 Flight track 4

MCS Inflow Conv

Water Vapor: 20 June

A key factor in nocturnal convection is the depth of the moist inflow, which can be aloft Sounding Susceptible to PBL-Based Convection Sounding Susceptible to Elevated Convection DVN (0000 UTC 9/12/2000) GRB (0000 UTC 9/12/2000) From Trier et al. 2002, abstract 130, Reading QPF meeting

Research Goals How common are bores and wave train events? What are the characteristics of these events? How are they generated and in what environments? How strong is the lifting and does it modify the inflow thermodynamics?

Research Technique Identify events in S-Pol and NEXRAD composites Independently identify events in MAPR and ISS surface data Identify event characteristics Link to environmental characteristics

Time of Occurrence

~18 bore and 8 S-Pol and MAPR wave events were S-Pol and MAPR bore/wave events ~18 bore and 8 S-Pol and MAPR wave events were observed. Bore events are observed in the later stages of LLJ periods when precipitation occurs.

BORE Example From MAPR 4 June Pre-bore height Post height

Bore Height Displacements Layer Height (km) Time (mins)

Implications and Speculations Undular bore-like disturbances are ubiquitous over this region when convection and low-level jets are present. Bore lifting varies. These disturbances can promote intense lifting with displacements of up to ~2 km. They initiate convection and help maintain existing systems by lifting their inflow (removing CIN) and by creating a deeper moist inflow. These disturbances surely contribute to the nocturnal precipitation maximum over this region allowing systems to cross over this unfavorable environment into more moist air.