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A Numerical Study of the Evolving Convective Boundary Layer and Orographic A Numerical Study of the Evolving Convective Boundary Layer and Orographic Circulation around the Santa Catalina Mountains in Arizona. Part II: Circulation around the Santa Catalina Mountains in Arizona. Part II: Circulation with Deep Convection Circulation with Deep Convection J. Cory Demko J. Cory Demko ([email protected]) ([email protected]) Bart Geerts Bart Geerts ([email protected]) ([email protected]) Department of Atmospheric Science, University of Wyoming Department of Atmospheric Science, University of Wyoming Abstra Abstra ct ct The Weather, Research, and Forecasting (WRF) modeling system is used for several IOPs during the Cumulus Photogrammetric, In situ and Doppler Observations (CuPIDO) campaign, conducted in summer 2006 around the Santa Catalina Mountains in southeast Arizona (Damiani et al. 2008), with the purpose to examine the interplay between boundary-layer convergence and orographic thunderstorms in a weakly- sheared environment subject to strong surface heating. This study builds on Part I (Demko et al. 2009b, presented as paper 10.4 at this conference, 4:45 pm on Tuesday), which examines thermally- forced orographic boundary-layer circulations without deep convection. The study is motivated by the fact that operational models poorly capture the timing and intensity of orographic convection, mostly due to inaccurate coupling between boundary-layer processes and cumulus convection over complex terrain. Model Setup and Data Model Setup and Data Sources Sources Detailed simulations using WRF-NMM model version 3.0.1.1 Detailed simulations using WRF-NMM model version 3.0.1.1 have been conducted on several days during CuPIDO. Model have been conducted on several days during CuPIDO. Model output validation data sources used in this study include output validation data sources used in this study include ISFF stations located around the mountain, KTUS soundings, ISFF stations located around the mountain, KTUS soundings, and WRF output, specifically the 24 hr period from 06 UTC and WRF output, specifically the 24 hr period from 06 UTC to 06 UTC the following day. to 06 UTC the following day. H orizontal grid resolution (km ) 9 3 1 Vertical levels 43 43 43 M icrophysics Lin etal. scheme Longwave radiation Rapid RadiativeTransferM odel Shortw ave radiation D udhia schem e Surfacelayer Eta sim iliarity Land surface N oah Land Surface M odel Planetary boundary layer Mellor-Yamada-Janjićscheme Cumulus parameterization Kain-Fritsch scheme, none, none Fig. 1: Fig. 1: Map (right) illustrates the ISFF Map (right) illustrates the ISFF station locations as well as WRF’s station locations as well as WRF’s closest grid point to that station used closest grid point to that station used for validation and calculation of for validation and calculation of mountain-scale convergence. Specific mountain-scale convergence. Specific location of canyons and ridges also location of canyons and ridges also shown. shown. Fig. 2: Fig. 2: Schematic transect Schematic transect (right) of the boundary-layer (right) of the boundary-layer flow (labeled flow (labeled v v n ), convective ), convective boundary layer depth ( boundary layer depth ( z z i , dashed , dashed line), temperature distribution line), temperature distribution and Cu development over an and Cu development over an isolated, heated mountain isolated, heated mountain without large-scale wind, based without large-scale wind, based upon CuPIDO observations (Demko upon CuPIDO observations (Demko et al. 2009a) and WRF et al. 2009a) and WRF simulations (Demko et al. simulations (Demko et al. 2009b). Part of the solenoidal 2009b). Part of the solenoidal circulation feeds the orographic circulation feeds the orographic cumulus cloud (solid squiggly cumulus cloud (solid squiggly lines). The dashed squiggly lines). The dashed squiggly lines indicate possible lines indicate possible convergent flow above the CBL, convergent flow above the CBL, associated with moist associated with moist convection convection. Table 1 Table 1 : Configurations of the WRF model, version 3.0.1.1 for : Configurations of the WRF model, version 3.0.1.1 for simulations of 06 August 2006 shown in this study. Multiple simulations of 06 August 2006 shown in this study. Multiple values indicate domains 1 (outer) through 3 (inner). values indicate domains 1 (outer) through 3 (inner). 1. 1. Deep moist convection overwhelms and interrupts the Deep moist convection overwhelms and interrupts the thermally-driven anabatic surface flow, due to cold pool thermally-driven anabatic surface flow, due to cold pool dynamics dynamics . After the Cb dissipates or moves of the mountain, . After the Cb dissipates or moves of the mountain, the mountain-scale surface convergence reestablishes, possibly the mountain-scale surface convergence reestablishes, possibly resulting in multiple convection cycles. WRF V.3 accurately resulting in multiple convection cycles. WRF V.3 accurately simulates this evolution, with two peaks of convective simulates this evolution, with two peaks of convective intensity on 6 Aug, in the early and the late afternoon. intensity on 6 Aug, in the early and the late afternoon. 2. 2. WRF simulations indicate that enhanced MSC does develop 1-2 WRF simulations indicate that enhanced MSC does develop 1-2 hours prior to orographic deep convection. hours prior to orographic deep convection. Deeper convection Deeper convection is not necessarily associated with stronger precursor is not necessarily associated with stronger precursor convergence, but does produce a more intense cold pool and convergence, but does produce a more intense cold pool and stronger surface divergence. stronger surface divergence. 3. 3. Even though the surface flow is divergent after a Cb Even though the surface flow is divergent after a Cb outbreak outbreak , the anomalous low may persist over the mountain, , the anomalous low may persist over the mountain, which reestablishes the PGF, and therefore, the anabatic flow. which reestablishes the PGF, and therefore, the anabatic flow. 4. 4. The mass budget (Fig. 9) The mass budget (Fig. 9) indicates a relationship between the indicates a relationship between the amount of moist convection and imbalance. Not shown are hours amount of moist convection and imbalance. Not shown are hours without moist convection which shows smaller residuals. These without moist convection which shows smaller residuals. These large imbalances are the subject to further analysis and may large imbalances are the subject to further analysis and may be attributed to evaporative/condensational cooling/warming be attributed to evaporative/condensational cooling/warming and errors associated with finite differencing. and errors associated with finite differencing. Case 1: 06 August 2006 Case 1: 06 August 2006 Fig. 7 Fig. 7 : (a) WRF’s Cloud top chronology (CTC) and the observed CTC : (a) WRF’s Cloud top chronology (CTC) and the observed CTC with various other WRF derived stability parameters for 6 August. with various other WRF derived stability parameters for 6 August. These parameters (LCL, LFC, CBL, MLCAPE, and MLCIN) were computed These parameters (LCL, LFC, CBL, MLCAPE, and MLCIN) were computed over a 30x30 km over a 30x30 km 2 box. The cloud top chronology tracks the highest box. The cloud top chronology tracks the highest cloud liquid water and ice having a value at least 0.01 gkm cloud liquid water and ice having a value at least 0.01 gkm -3 -3 . The . The geographic location of the highest cloud element in WRF is shown geographic location of the highest cloud element in WRF is shown Conclusi Conclusi ons ons Fig. 3 Fig. 3 : Conceptual view of the diurnal evolution of a weakly-capped CBL : Conceptual view of the diurnal evolution of a weakly-capped CBL and thermally-forced circulation over an isolated mountain under and thermally-forced circulation over an isolated mountain under negligible mean wind and enough moisture for shallow to mediocre cumulus negligible mean wind and enough moisture for shallow to mediocre cumulus development (the focus of part I, Demko et al. 2009b). The horizontal development (the focus of part I, Demko et al. 2009b). The horizontal (vertical) dimensions of the west-east cross section are ~50 km (~5 km). (vertical) dimensions of the west-east cross section are ~50 km (~5 km). The times shown are: (a) near sunrise; (b) shortly before orographic The times shown are: (a) near sunrise; (b) shortly before orographic cumulus development; (c) orographic cumulus phase, typically around cumulus development; (c) orographic cumulus phase, typically around solar noon; (d) near sunset. Red contours are dry isentropes, purple solar noon; (d) near sunset. Red contours are dry isentropes, purple contours indicate variations of the height of the 850 hPa surface (Z contours indicate variations of the height of the 850 hPa surface (Z 850 850 ) ) and thus the direction of the pressure gradient, the bold grey contour and thus the direction of the pressure gradient, the bold grey contour is the top of the CBL or the nocturnal boundary-layer (NBL), and the is the top of the CBL or the nocturnal boundary-layer (NBL), and the The schematic on The schematic on the left shows the left shows the diurnal the diurnal evolution of the evolution of the thermally-forced thermally-forced circulation with circulation with mediocre moist mediocre moist convection (Part convection (Part I). In this I). In this poster (Part II) poster (Part II) we examine the we examine the two-way two-way interaction interaction between the BL between the BL circulation and circulation and deep convection. deep convection. Fig. 4 Fig. 4 : : 21 21 vertical vertical cross cross sectional sectional average of average of θ θ ’ west,east west,east , u , u ’ , , w, w, and PBL and PBL height for height for 12 (a), 15 12 (a), 15 (b), 18 (c), (b), 18 (c), and 21 (d) and 21 (d) UTC 06 UTC 06 August 2006. August 2006. Also shown Also shown are profiles are profiles of the mean of the mean θ θ west west (solid), (solid), θ θ east east (dashed) (dashed) (profiles on (profiles on the left) the left) and u and u (profile on (profile on the right). the right). By 21 UTC, the PBL has deepened to ~675 hPa over the mountain. The warm dome By 21 UTC, the PBL has deepened to ~675 hPa over the mountain. The warm dome is approximately 15 km wide, extends over the majority of the CBL, and has is approximately 15 km wide, extends over the majority of the CBL, and has strength of up to 2 K. The anabatic flow is rather symmetric on both sides strength of up to 2 K. The anabatic flow is rather symmetric on both sides with maxima with maxima u’ u’ located near the surface and on the western slopes. The anabatic located near the surface and on the western slopes. The anabatic circulation collides slightly downwind (west) of the crest, and is the main circulation collides slightly downwind (west) of the crest, and is the main focus of precipitation and a deep Cb burst ( focus of precipitation and a deep Cb burst ( 23 UTC 06 Aug – 01 UTC 07 Aug 23 UTC 06 Aug – 01 UTC 07 Aug ). ). Fig. 5 Fig. 5 : : Time versus Time versus height plot of mountain- height plot of mountain- scale (30x30 km scale (30x30 km 2 ) ) convergence (color convergence (color shaded), mean vertical shaded), mean vertical velocity as inferred from velocity as inferred from the convergence field the convergence field (black solid and dotted (black solid and dotted lines), and PBL height lines), and PBL height (black dashed). Note the (black dashed). Note the daytime deepening of the daytime deepening of the PBL in sync with the PBL in sync with the deepening of MSC. Deep deepening of MSC. Deep convection starting at 23 convection starting at 23 UTC produces low-level UTC produces low-level subsidence and near- subsidence and near- surface divergence (cold surface divergence (cold pool dynamics). Local pool dynamics). Local solar noon is at 19:30 solar noon is at 19:30 UTC, sunrise at 12:35 UTC, sunrise at 12:35 UTC, sunset at 02:25 UTC. UTC, sunset at 02:25 UTC. Fig. 6 Fig. 6 : Hydrostatic pressure : Hydrostatic pressure difference between Mt. Lemmon difference between Mt. Lemmon and closed boxes (black, left and closed boxes (black, left axis) and subsequent surface axis) and subsequent surface convergence (grey, right convergence (grey, right axis) for (a) 100, (b) 400, axis) for (a) 100, (b) 400, (c) 900, and (d) 1600 km (c) 900, and (d) 1600 km 2 boxes for period 06 UTC 06 boxes for period 06 UTC 06 August through 06 UTC 07 August through 06 UTC 07 August. The vertical lines August. The vertical lines show the time of minimum & show the time of minimum & maximum values, when the PGF maximum values, when the PGF becomes directed toward the becomes directed toward the mountain, and when surface mountain, and when surface flow becomes convergent. The flow becomes convergent. The average height MSL of each average height MSL of each box is shown in the upper box is shown in the upper left side of each figure. left side of each figure. Fig. 8 Fig. 8 : 2 m potential temperature (color shaded surface), 10 m wind : 2 m potential temperature (color shaded surface), 10 m wind (barbs), and cloud liquid or frozen water isosurface of 0.01 gkm (barbs), and cloud liquid or frozen water isosurface of 0.01 gkm -1 -1 for WRF for WRF forecast hours 19, 20, 21 (top/left to right), 22, 23 UTC 06 August, and forecast hours 19, 20, 21 (top/left to right), 22, 23 UTC 06 August, and 00 UTC 07 August (bottom/left to right). Also illustrated are 1 hr 00 UTC 07 August (bottom/left to right). Also illustrated are 1 hr accumulated precipitation contours over terrain in intervals of 0.01, 0.1, accumulated precipitation contours over terrain in intervals of 0.01, 0.1, 0.25, 0.5 inches respectively. Cloud isosurfaces are only showed within 0.25, 0.5 inches respectively. Cloud isosurfaces are only showed within the 900 km the 900 km 2 box centered on Mt. Lemmon to reduce image clutter. Notice how box centered on Mt. Lemmon to reduce image clutter. Notice how the majority of convection and subsequent precipitation is centered upon the majority of convection and subsequent precipitation is centered upon Pusch ridge, where the anabatic circulation belts collide slightly Pusch ridge, where the anabatic circulation belts collide slightly downwind of the peaks generating a narrow column of upward motion. downwind of the peaks generating a narrow column of upward motion. Fig. 9 Fig. 9 : Mass budget analysis for hours 19 UTC 06 August – 00 UTC 07 August : Mass budget analysis for hours 19 UTC 06 August – 00 UTC 07 August for 3 closed boxes performed over the 900 km for 3 closed boxes performed over the 900 km 2 area with vertical area with vertical dimensions of box 1 = (z dimensions of box 1 = (z mid-PBL mid-PBL to z to z sfc sfc ), box 2 = (z ), box 2 = (z PBL-top PBL-top to z to z mid-PBL mid-PBL ), and box 3 ), and box 3 =(z =(z cloud top cloud top to z to z PBL-top PBL-top ) which are represented by the horizontal planes. Flux ) which are represented by the horizontal planes. Flux values are in 10 values are in 10 6 kgs kgs -1 -1 and arrows indicate flux direction. Cloud and arrows indicate flux direction. Cloud isosurfaces of 0.01 gkm isosurfaces of 0.01 gkm -1 -1 are also shown. are also shown.
