Polarimetric Radar Convective Cell Tracking Reveals Large Sensitivity of Cloud Precipitation and Electrification Properties to CCN

Here we apply the cell tracking methodology, with details about the algorithm to be found in Hu et al, 2017, to quantifying aerosol and thermodynamic factors affecting the vigor and the time-height evolution of hydrometeors and electrification properties of convective cells. Benefitting from the Dual-polarimetric NEXRAD radar network, we composite more than 5000 well-tracked cells among three radars (at Houston, Lubbock and Oklahoma City), stratified by CCN, CAPE and land/sea locations. The analyzed cell properties include Z, Z_DR, Kdp, and ρ_hv, Dm (raindrop diameter) and Nw (raindrop concentration) by the algorithm of Bringi et al. (2003). Lightning Mapping Array (LMA) data is also included in the analysis, which provides a 3D structure of lightning occurrence and RF power. The contrasting CCN conditions over marine, land, pristine and polluted areas are identified based on the satellite retrieval technique described in Rosenfeld et al. (2016). The results show that more CCN are associated with:

1. Increased echo top height, manifesting the invigoration effect.

2. Enhanced reflectivities, especially above the freezing level at around 4.5 km.

3. Raindrop sizes at the initial stage increase at the expense of their concentrations, due to the smaller cloud droplets and suppressed coalescence.

4. Larger propensity for hail.

5. Lightning sources increase with greater CCN concentration and is likely due to the delayed warm rain process and enhanced mixed phase process under more CCN condition, when activated CCN into cloud droplets is too high (> ~1000 cm^-3) the glaciation is delayed too much and leave little ice at lower levels and thus decrease lightning activity.

6. Land pristine clouds have fewer lightning sources than polluted clouds. Marine pristine clouds seldom have lightning

Increased CAPE had a similar effect to the effect of added CCN.

References

[1] Bringi, V. et al., J. Atmos. Sci., 60, 354-365. (2003)

[2] Rosenfeld, D. et al., Proc. Natl. Acad. Sci., 113, 5828-5834. (2016)

[3] Hu, J. et al., in preparation.