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...N and l are derived from the predicted q and specified N0 and m for each species by rearranging terms in (2) and (3). Following many onemoment schemes (e.g., Lin et al. 1983; Rutledge and Hobbs 1984; =-=Dudhia 1989-=-; Grabowski 1998), N0 is constant for a given species. Values are taken from existing schemes described in the literature and shown in Table 1. Note that while most one-moment schemes use constant val...

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...pecified for rain, snow, and graupel, and N and l are derived from the predicted q and specified N0 and m for each species by rearranging terms in (2) and (3). Following many onemoment schemes (e.g., =-=Lin et al. 1983-=-; Rutledge and Hobbs 1984; Dudhia 1989; Grabowski 1998), N0 is constant for a given species. Values are taken from existing schemes described in the literature and shown in Table 1. Note that while mo...

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...ciated with differences in the rain size distribution parameters (the rain intercept parameter N0r and the rain slope parameter lr) between the runs. The rain evaporation rate is given by (similar to =-=Rutledge and Hobbs 1983-=-; Reisner et al. 1998) ›qr ›t evap 5 2pN0rDy(S 1) A01B0 3 f 1 l2r 1 f 2 arr ma 1 2 S 1 3 c G(br/21 5/2) lbr /21 5/2r " # , (4) where Dy is the diffusivity of water vapor in air, S is the liqui...

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... Further investigation of the impact of the graupel microphysics is beyond the scope of this study. The change in snow and graupel number concentration due to melting and sublimation (not included in =-=Reisner et al. 1998-=-) is calculated by assuming that the relative change in number concentration is the same as the change in mixing ratio due to these processes following Ferrier (1994). FollowingMCK and Ferrier (1994),...

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... size spectra rather than just one (i.e., the mass mixing ratio). Several two-moment schemes have been developed and utilized in a variety of applications (e.g., Koenig and Murray 1976; Ferrier 1994; =-=Meyers et al. 1997-=-; Khairoutdinov and Kogan 2000; Seifert and Beheng 2001; Milbrandt and Yau 2005; Morrison et al. (2005, hereafter MCK). These schemes predict the number concentrations and mixing ratios of the hydrome...

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...bove the melting layer. Changes in the interaction between the cold pool and ambient wind shear with the reduced latent cooling may also impact the intensity and character of the convective updrafts (=-=Rotunno et al. 1988-=-; Weisman and Rotunno 2004). The stronger convective updrafts in the sensitivity simulation with reduced evaporation are associated with a reduced rearward flux of positively buoyant air into the stra...

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...he hydrometeor size spectra rather than just one (i.e., the mass mixing ratio). Several two-moment schemes have been developed and utilized in a variety of applications (e.g., Koenig and Murray 1976; =-=Ferrier 1994-=-; Meyers et al. 1997; Khairoutdinov and Kogan 2000; Seifert and Beheng 2001; Milbrandt and Yau 2005; Morrison et al. (2005, hereafter MCK). These schemes predict the number concentrations and mixing r...

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...ipitation are common in both midlatitude and tropical environments, and have been extensively studied by numerous researchers (e.g., Fujita 1955; Zipser 1969; Ogura and Chen 1977; LeMone et al. 1984; =-=Houze 1989-=-; Biggerstaff and Houze 1991, 1993). These studies have suggested several common morphological features described by the conceptual model of Biggerstaff and Houze (1991, see their Fig. 18). These feat...

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...ve regions is consistent with surface disdrometer measurements in midlatitude and tropical systems indicating a sharp decrease in N0r between these two regions, referred to previously as the N0 jump (=-=Waldvogel 1974-=-; Tokay and Short 1996; Atlas et al. 1999). Decreasing the value of N0r specified in 1-M to the mean value predicted in 2-M for the stratiform region (2 3 106 m24) significantly increased the amount o...

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...nvestigated by Tokay and Short (1996) and Atlas et al. (1999). These studies showed that N0r decreases rapidly during the transition from convective to widespread stratiform rain (e.g., see Fig. 4 in =-=Tokay and Short 1996-=-); Waldvogel (1974) termed this decrease in N0r the ‘‘N0 jump.’’ Tokay and Short (1996) found relatively high evaporation rates in the convective region compared to the stratiform region, and conclude...

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...herein. The trailing stratiform region is associated with a mesoscale updraft at mid- and upper levels, and mesoscale downdraft on the order of tens of centimeters per second. Modeling studies (e.g., =-=Fovell and Ogura 1988-=-; Tao *The National Center for Atmospheric Research is sponsored by the National Science Foundation. Corresponding author address:HughMorrison, National Center for Atmospheric Research, 3450 Mitchell ...

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...udies have attempted to simulate squall lines with an enhanced region of trailing stratiform precipitation using cloud-system-resolving models (e.g., Fovell and Ogura 1988; Lafore and Moncrieff 1989; =-=McCumber et al. 1991-=-; Ferrier et al. 1995). Fovell and Ogura (1988) and McCumber et al. (1991) found that inclusion of ice microphysics enhanced stratiform precipitation relative to liquid-only schemes, because of an inc...

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...ent. Numerous studies have attempted to simulate squall lines with an enhanced region of trailing stratiform precipitation using cloud-system-resolving models (e.g., Fovell and Ogura 1988; Lafore and =-=Moncrieff 1989-=-; McCumber et al. 1991; Ferrier et al. 1995). Fovell and Ogura (1988) and McCumber et al. (1991) found that inclusion of ice microphysics enhanced stratiform precipitation relative to liquid-only sche...

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...ntroduction Squall lines with trailing stratiform precipitation are common in both midlatitude and tropical environments, and have been extensively studied by numerous researchers (e.g., Fujita 1955; =-=Zipser 1969-=-; Ogura and Chen 1977; LeMone et al. 1984; Houze 1989; Biggerstaff and Houze 1991, 1993). These studies have suggested several common morphological features described by the conceptual model of Bigger...

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...aries are free slip with zero vertical velocity. Surface fluxes are zero and radiative transfer is neglected. Previous studies have shown some impact of radiative transfer on squall-line development (=-=Tao et al. 1993-=-, 1996), but these impacts are neglected here for simplicity. The model is initialized with the environmental temperature and moisture profiles used by Weisman and Klemp (1982, 1984) and others (see F...

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...erived from the predicted q and specified N0 and m for each species by rearranging terms in (2) and (3). Following many onemoment schemes (e.g., Lin et al. 1983; Rutledge and Hobbs 1984; Dudhia 1989; =-=Grabowski 1998-=-), N0 is constant for a given species. Values are taken from existing schemes described in the literature and shown in Table 1. Note that while most one-moment schemes use constant values of N0, it is...

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...have suggested enhanced subsidence in the transition zone associated with dynamically and/or microphysically driven downdrafts (i.e., by evaporative cooling and precipitation loading; e.g., Houze and =-=Rappaport 1984-=-; Smull and Houze 1985; Srivastava et al. 1986). The diagnostic modeling study of Rutledge and Houze (1987) suggested that the location of the heaviest stratiform precipitation could be explained by t...

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...tion of two moments of the hydrometeor size spectra rather than just one (i.e., the mass mixing ratio). Several two-moment schemes have been developed and utilized in a variety of applications (e.g., =-=Koenig and Murray 1976-=-; Ferrier 1994; Meyers et al. 1997; Khairoutdinov and Kogan 2000; Seifert and Beheng 2001; Milbrandt and Yau 2005; Morrison et al. (2005, hereafter MCK). These schemes predict the number concentration...

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...rated by mesoscale ascent in the stratiform region. The mesoscale downdraft appears to be associated with evaporation of precipitation falling into unsaturated air beneath the stratiform cloud (e.g., =-=Brown 1979-=-), which may be enhanced by melting (Leary and Houze 1979). Rutledge et al. (1988) found that the mesoscale downdraft was strongest just beneath the melting layer of the stratiform region in the area ...

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...ling stratiform precipitation are common in both midlatitude and tropical environments, and have been extensively studied by numerous researchers (e.g., Fujita 1955; Zipser 1969; Ogura and Chen 1977; =-=LeMone et al. 1984-=-; Houze 1989; Biggerstaff and Houze 1991, 1993). These studies have suggested several common morphological features described by the conceptual model of Biggerstaff and Houze (1991, see their Fig. 18)...

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...rrower and less intense than observed, and Fovell and Ogura (1988) further noted the lack of a clear transition zone of low radar reflectivity in their simulation as was observed. Subsequent studies (=-=Sui et al. 1998-=-; Lang et al. 2003) focused on the ratio of stratiform and convective precipitation; these studies also suggested a bias toward heavy (convective) rain rates, although Lang et al. (2003) note that the...

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...quall lines with trailing stratiform precipitation are common in both midlatitude and tropical environments, and have been extensively studied by numerous researchers (e.g., Fujita 1955; Zipser 1969; =-=Ogura and Chen 1977-=-; LeMone et al. 1984; Houze 1989; Biggerstaff and Houze 1991, 1993). These studies have suggested several common morphological features described by the conceptual model of Biggerstaff and Houze (1991...

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...but these impacts are neglected here for simplicity. The model is initialized with the environmental temperature and moisture profiles used by Weisman and Klemp (1982, 1984) and others (see Fig. 1 in =-=Weisman and Klemp 1982-=-), which are broadly typical of the environment of midlatitude, continental squall lines although they are relatively moist at midlevels. The initial convective available potential energy (CAPE) is 22...

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... Ln., Boulder, CO 80307. E-mail: morrison@ucar.edu MARCH 2009 MORR I SON ET AL . 991 DOI: 10.1175/2008MWR2556.1 2009 American Meteorological Society et al. 1993) and thermodynamic retrievals (e.g., =-=Hauser et al. 1988-=-) indicate that air at mid- and upper levels of the trailing stratiform region is positively buoyant, at least in part due to the advection of positively buoyant air from the convective region in the ...