FA scientific documentation

physics/docs/pdftxt/HWRF_FAMP.txt

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+/**
+\page HWRF_famp HWRF Ferrier-Aligo (FA) Microphysics Scheme
+\section des_famp Description
+
+The Ferrier-Aligo (FA) microphysics (Aligo et al. 2018 \cite aligo_et_al_2018) is a single
+moment scheme predicting mass mixing ratios of rain water (\f$q_r\f$), cloud water (\f$q_c\f$),
+cloud ice (\f$q_i\f$), and snow-graupel (\f$q_s\f$). The FA scheme is currently used operationally
+in the North American Mesoscale Forecast System (NAM; including the parent 12-km domain, the 3-km
+NAM nests, and the 1.5km fire weather nest), the Hurricane Weather Research and Forecasting Model (HWRF),
+the Hurricanes in a Multi-scale Ocean-coupled Non-hydrostatic Model (HMON), and the High-Resolution
+Window (HiResW) Non-dydrostatic Multiscale Model on the B grid (NMMB). The FA scheme advects each 
+species separately in the NAM nests, and advects the total condensate in the 12-km parent NAM,HiResW NMMB,
+HWRF, and HMON.
+
+Unique to the FA scheme is the calculation of a diagnostic array called the "rime factor" (RF), which
+represents the degree of riming onto snow-graupel, and takes into account the temperature of the ice particle, 
+the impact velocity of the cloud droplet on the ice particle, and the size of the cloud droplet. For all
+practical purposes, one can categorize precipitation ice as snow, graupel, or hail, similar to the ice
+species predicted in other microphysical schemes based on the value of the RF. For example, an RF = 1 
+represents unrimed snow; lightly rimed snow occurs when 1 < RF < 2; heavily rimed snow when 2< RF \f$\leqslant\f$ 5;
+graupel when 5 < RF < 10; and frozen drops or hail when RF \f$geqslant\f$ 10. In reality, the RF knows 
+no arbitrary cutoff between different ice categories, and the categorizations above are somewhat subjective.
+Figure 1 is a schematic illustration of the FA scheme processes and each process is described in Table 1.
+
+\image html FA_MP_schematic.png "Figure 1: Local Land-atmosphere Interaction (courtesy of Michael Ek)" width=10cm
+
+Owing to operational computation constraints, and unique to the FA scheme, the sedimentation process 
+does not use finite differencing of precipitation fluxes in the vertical in order to circumvent the 
+requirement that small time steps be used in order to maintain numerical stability, particularly since 
+the vertical resolution often increases dramatically near the ground. The algorithm is instead based upon
+a partitioning of precipitation already present in the grid box at the beginning of the time step and the
+precipitation entering the grid box from above at the end of the time step. A more detailed description 
+of the sedimentation algorithm can be found in Aligo et al. (2018, appendix D).
+
+An algorithm was developed in FA to improve stratiform rainfall by allowing the rain intercept parameter,
+\f$N_{or}\f$, to vary with height and the mean drop diameter to be fixed below melting layers. This is 
+different from other single-moment microphysics schemes (WSM6 and Lin) that assume a constant value for
+\f$N_{or}\f$. The algorithm in the FA scheme, simular to what is done in the Thompson scheme \cite thompson_et_al_2008,
+assumes that a snow-graupel particle about to enter the melting layer from above has the same mean mass
+as a drop formed from melting below the melting layer. The mean drop diameter calculated below the melting layer
+acts as the lower limit for the mean drop sizes as the rain descends to lower levels. This algorithm is only
+active if 1) the snow-graupel density above the melting level (i.e.\f$T_c<0^{o}C\f$) is \f$<225kg m^{-3}\f$ 
+(which corresponds to an RF=10), 2) the rain content does not exceed \f$1gm^{-3}\f$, and 3) there is vertical
+continuity of the rain at lower levels with the rain that formed from melting ice.
+
+The FA scheme also uses a drizzle parameterization in order to minimize the spatial extent of light (<20dBZ)
+reflectivity echoes that developed at the top of moist boundary layers, over the Southeastern U.S., within
+warm conveyor belts, and over ocean areas covered by stratocumulus in the NMMB. The drizzle parameterization
+uses a variable \f$N_{or}\f$ following Westbrook et al. (2010) \cite westbrook_et_al_2010, and approach 
+conceptually similar to that described in Thompson et al.(2008) for drizzle. Figure 2a
+
+
+
+
+\section intra_famp Intraphysics Communication
+
+ + For grid-scale condensation and evaporation of cloud process (\ref arg_table_zhaocarr_gscond_run)
+ + For precipitation (snow or rain) production (\ref arg_table_zhaocarr_precpd_run)
+
+\section gen_famp  General Algorithm
+ + \ref general_gscond
+ + \ref general_precpd
+
+
+*/