Hurricane Dorian Outer Rain Band Observations and 1D Particle Model Simulations: A Case Study

Abstract

The availability of high quality surface observations of precipitation and volume observations by polarimetric operational radars make it possible to constrain, evaluate, and validate numerical models with a wide variety of microphysical schemes. In this article, a novel particle-based Monte-Carlo microphysical model (called McSnow) is used to simulate the outer rain bands of Hurricane Dorian which traversed the densely instrumented precipitation research facility operated by NASA at Wallops Island, Virginia. The rain bands showed steady stratiform vertical profiles with radar signature of dendritic growth layers near −15 °C and peak reflectivity in the bright band of 55 dBZ along with polarimetric signatures of wet snow with sizes inferred to exceed 15 mm. A 2D-video disdrometer measured frequent occurrences of large drops >5 mm and combined with an optical array probe the drop size distribution was well-documented in spite of uncertainty for drops <0.5 mm due to high wind gusts and turbulence. The 1D McSnow control run and four numerical experiments were conducted and compared with observations. One of the main findings is that even at the moderate rain rate of 10 mm/h collisional breakup is essential for the shape of the drop size distribution.

Testing the Drop-Size Distribution-Based Separation of Stratiform and Convective Rain Using Radar and Disdrometer Data from a Mid-Latitude Coastal Region

“…The bright-band thickness and the dBZ peak (>55 dBZ) were high. Bringi et al [31] have examined this particular case using 1D Particle Model Simulations.…”

“…We consider three events here: (i) a category-1 Hurricane event (Dorian), whose outer rainbands passed over the WFF site on 06 September 2019 [30,31], (ii) a squall-like event with an 'ill-defined' line convection which occurred on 14 October 2019, and (iii) a more widespread event with small embedded convective cells on 16 October 2019.…”

Separation of Stratiform and Convective Rain Types Using Data from an S-Band Polarimetric Radar: A Case Study Comparing Two Different Methods

“…but Z dr decreases, indicating, once again, the possible occurrence of drop break process but also indicating an increase in number concentration (per unit volume). These features were also observed in the stratiform rain regions of the outer rain-bands of Category-1 Hurricane Dorian (again over Wallops; [20]). A 1D MonteCarlo microphysical model using the super-particle concept (named McSnow; [21]) together with radiosonde data as model input also showed the importance of drop break-up even in light to moderate rain rates, being consistent with the radar observations [20].…”

“…These features were also observed in the stratiform rain regions of the outer rain-bands of Category-1 Hurricane Dorian (again over Wallops; [20]). A 1D MonteCarlo microphysical model using the super-particle concept (named McSnow; [21]) together with radiosonde data as model input also showed the importance of drop break-up even in light to moderate rain rates, being consistent with the radar observations [20]. The corresponding CFADs for NW and Dm are shown in Figure 5.…”

Measurements of Rainfall Rate, Drop Size Distribution, and Variability at Middle and Higher Latitudes: Application to the Combined DPR-GMI Algorithm

“…(d) Simulations of gamma DSDs with uncorrelated N W , D m , and shape parameter (µ). (e) The outer rain bands of: (a) Category-1 Hurricane Dorian, described by Thurai et al [34] and modeled using a cloud particle model by Bringi et al [35], which traversed the WFF disdrometer network site for ≈8 h; (b) tropical storm Irma (<14 h) near the Huntsville site; (c) tropical depression Nate, which was very shallow at times with negligible echo above the melting layer and 'pure' warm rain at times (overall <16 h) near Huntsville. Figure 1 shows the locations marked as WFF and HSV.…”