Part 3 Selected Modeling and Preliminary Confrontation with VOCALS Hypothesis

Transcription

1 Part 3 Selected Modeling and Preliminary Confrontation with VOCALS Hypothesis

2 Transition to deep convection Shallow convection Transition to shallow convection Coastal clearing Aerosol VOCALS Paradigm C. R. Mechoso

3 Synoptic Variability in VOCALS Region Rhea George EOF Analysis of SLP (NCEP reanalysis data)

4 Zooming in on PC1 to note behavior during VOCALS-REx (Oct 15-Nov 30) Time (days) in 2008 Rhea George

5 Composite difference plots on SLP dominant mode of variability N d LWP Temperature Advection Low Cloud Fraction Omega Rhea George

6 Multi-satellite data for model evaluation M. Brunke and X. Zeng, U. Arizona These plots from October 1, 2008 onward and a detailed description of what s in these plots available at zona.edu/~brunke/v OCALS/

7 Preliminary model evaluation using pre-vocals data: A detailed description of this figure available at

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11 Met Office models in VOCALS Phil Brown Global (40km resolution) Unified Model (UM) products supplied daily to VOCALS Field Catalog. 17km resolution Regional UM ran on most days and also supplied the Field Catalog. Missing data have been supplied post-campaign. NAME model provided dispersion forecasts from both the Global and Regional (when available) models.

12 Unified Model performance example 1 Some cloud inhomogeneities are artefacts associated with change of BL height between grid levels (increase from 38 to 70 model levels in 2009). Misses larger POC/rift regions on this occasion but gets some realistic structure parallel to Peru coast

13 Unified Model performance example 2 Good reproduction of large-scale structure at S edge of Sc sheet GOES visible 1515 UTC 7/11/2008

14 Modelling - PreVOCA GOAL: Assess the forecast skill and biases of global/ regional model simulations of SE Pacific boundary-layer clouds and aerosols on diurnal and longer timescales. WHAT? Daily hindcasts for October 2006 over the SE Pacific, compated with satellite and ESRL cruise data for model assessment and improvement. WHO? 14 modeling groups using regional and global models, including NCAR, GFDL climate models run in forecast mode. WHEN? Data submission complete; analysis mostly complete, journal submission early FOLLOW-UP? Second phase (VOCA) will repeat using REx period, with aerosol/chemical/microphysics focus. COORDINATORS: Wyant, Bretherton, Wood, Mechoso

15 Pre-VOCA Model NRL COAMPS COLA RSM IPRC Reg_CM (IRAM) PNNL (WRF-Chem) UCLA (WRF) U. Chile (WRF) ECMWF oper. 3-12h forecast ECMWF 5-day forecast ECMWF coupled fcst ensemble GMAO GEOS-5 DAS JMA 24-30h forecast NCEP oper h forecast UKMO oper h forecast LMDZ NCAR CAM3.5/6 GFDL UCLA 7.3 Levels / Resolution [km] (inner domain) 81 (27) 50 ~25 45 (15) 45 (15) 45 ~25 ~40 ~125 ~56 ~60 ~38 ~

16 Finding I: Models agree on large-scale dynamics, but less well on cloud cover Winds Regional Global fcst Climate m s hpa subsidence Pa s-1

17 Finding October II: PBL varies soundings more among at IMET climate BUOY than forecast locationmodels! (20S, 85W) Regional Global forecast Climate UCLA AGCM Climate (LMDZ is quasi-regional) Humidity (20S, 85W) UCLA AGCM

18 Surface Fluxes from VOCALS-REX S. de Szoeke GFDL CM2.1 iroam UCLA AGCM

19 SEP ocean heat budget: a substantial contribution from oceanic variability. T. Toniazzo. IMET buoy: over more than 3 years, either the heat budget is not maintained, or it is via rectification of variability. Task: understand time-scales, length-scales, structures, mechanisms, processes... HiGEM GCM: the vertically integrated oceanic heat budget is consistent with Bob Weller's observational estimate. This is accompanied by surface SST climatology very close to observed.

20 Contributions from different time-scales u "T = u "T + u' "T' + u' "T + u "T' rectifying non-rectifying u' = u'1 + u'2 etc.; spatially or temporally filtered components Geostrophic transients with 4 month < P < 1 yr are dominant Organised in large-scale pattern Interannual Interseasonal subseasonal 15S 15S 15S 20S 20S 20S 25S 25S 25S 95W 90W 85W 80W 75W 95W 90W 85W 80W 75W 95W 90W 85W 80W 75W

21 A conceptual model: transient displacements of a sharp salinity ( spiciness ) front Geostrophic temperature advection anomalies: u' "T' ~ "S' x "T' As long as the displacement is larger than the width of the fronts, the associated advection tendencies generate a rectifying dipolar pattern

22 Large-eddy Simulations of Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus Hailong Wang and Graham Feingold NOAA Earth System Research Lab, Boulder, CO Objectives: To examine how aerosol-cloud-drizzle interactions and dynamical feedbacks affect the formation and evolution of Pockets of Open Cells (POCs); To study the microphysics and dynamics at open-/closed-cell boundaries; To help inform analyses of POC observations emanating from VOCALS-REx and in turn to gain observational feedbacks to refine our simulations and our understanding of POC-related processes. Model: Large-eddy simulations (LES) are performed using the Weather Research and Forecasting (WRF) model; New in the WRF model: 2-moment microphysics (Feingold et al. 1998) and monotonic advection scheme (Wang et al. 2008); Case: The 9th GCSS LES intercomparison case (Ackerman et al. 2008) -- RF02 of the Second Dynamics and Chemistry of Marine Sc (DYCOMS-II) Experiments: N65 and N500 (initial CCN concentration of 65 and 500 cm -3 ); domain size: 60!60 km 2. N (Initial CCN linearly increasing from 65 to 300 cm -3 in x-direction); domain size: 180!60 km 2. Cyclic boundary conditions; dx=dy=300 m, dz=30 m, and dt=3 s.

23 Impact of drizzle on the formation and evolution of mesoscale open cells (Wang and Feingold 2008a) Cases: N65 and N500 Cloud albedo w and rain rate at 200 m Time (h) Dark areas have very little dynamical support. Drizzle and downdrafts Reflective open-cell walls Updraft rings The shape of open cells matches the ring-like structures in w fields, which are associated with embedded drizzle clusters; Simulation results support the hypothesis that drizzle plays a critical role in the formation and evolution of open cells. The dynamic response to evaporative cooling and moistening associated with drizzle manifests itself in cellular organization in the turbulent flow, and promotes and sustains the formation of an open cellular structure in clouds.

24 The microphysics and dynamics at open-/close-cell boundaries (Wang and Feingold 2008b) Cloud albedo (top); w and rain rate (black lines) at 300 m (bottom) Case: N Total particle # conc. and q v perturbation (top); cloud, rain and wind vector (bottom) x-z cross-section CCN+N d, cm -3 q v Cloud Drizzle Drizzle suppressed on the clean side Drizzle promoted in the closed cells Mesoscale circulation near open-/closed-cell boundaries characterized by an x-direction outflow from open-cell regions to closed cells in lower boundary layer and a return inflow in the cloud layer, which is induced by the contrast in CCN concentration and changes in drizzle; The circulation transports moisture to closed cells and CCN to open cells; Drizzle on the clean side of the boundary is suppressed, while drizzle at the closed-cell boundary is promoted due to the dilution of CCN and the moisture supply.

25 Atmospheric modeling at the Instituto Geofísico del Perú K. Takahashi 1000 hpa wind for Oct 5-15, 2008 NCAR/PSU MM5 v.3-7 Run for VOCALS- Rex Peru period #x = 45, 15, 5 km. #x = 5 km Radio-soundings m/s The results show coastally confined (within 50 km) alongshore nearsurface jets associated with coastal topography Coastal jets Andes mountains Coastal range m PBL: Gayno-Seaman; Cu: Kain-Fritsch; shallow conv. ; Rad: CCM2

26 Atmospheric modeling at the Instituto Geofísico del Perú K. Takahashi Simulation reproduces the coastal clearing. Cloud water path and inversion level Hydraulic effects on the inversion height associated with the coastal jets appear to be related to the clearing. 950 hpa 955 hpa 960 hpa #x = 5 km g/m 2 Comparison with field measurements and further experiments and sensitivity tests are in process. 945 hpa 940 hpa Coastal clearing Depressed inversion coincident with the jets PBL: Gayno-Seaman; Cu: Kain-Fritsch; shallow conv.; Rad: CCM2

27 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Aerosol-Cloud-Precipitation Hypothesis #1: Variability in the physicochemical properties of aerosols has a measurable impact upon the formation of drizzle in stratocumulus clouds over the SEP Synthesis: REx and recent CloudSat observations support this hypothesis. In areas with higher accumulation mode aerosol concentrations (or, alternatively higher droplet concentrations), stratocumulus clouds of a given liquid water path (LWP) drizzle less. However, LWP is also a critical control on drizzle.

28 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Aerosol-Cloud-Precipitation Hypothesis #1: Variability in the physicochemical properties of aerosols has a measurable impact upon the formation of drizzle in stratocumulus clouds over the SEP Synthesis: REx and recent CloudSat observations support this hypothesis. In areas with higher accumulation mode aerosol concentrations (or, alternatively higher droplet concentrations), stratocumulus clouds of a given liquid water path (LWP) drizzle less. However, LWP is also a critical control on drizzle.

29 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Aerosol-Cloud-Precipitation Hypothesis #2: Precipitation is a necessary condition for the formation and maintenance of pockets of open cells (POCs) within stratocumulus clouds. Synthesis: All POCs sampled in REx contained drizzling cells, but the surrounding overcast stratocumulus commonly also supported some drizzle. Thus drizzle seems necessary, but not sufficient, to cause transition of closed-cell convection into a POC.

30 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Aerosol-Cloud-Precipitation Hypothesis #3: The small effective radii measured from space over the SEP are primarily controlled by anthropogenic, rather than natural, aerosol production, and entrainment of polluted air from the lower free-troposphere is an important source of cloud condensation nuclei (CCN). Synthesis: Measured cloud droplet concentrations were closely correlated with those of accumulation mode aerosol particles. Such aerosols mainly seemed to derive from pollution injected into the boundary layer at the coast, but entrainment of thin tongues of high SO 2 (and other mainly gaseous pollutants) far offshore may also promote the growth of Aitken mode aerosol particles to CCN size. Atmospheric DMS concentrations were not strongly elevated near the coastal upwelling zone. Atmospheric photochemical destruction of DMS, however, seemed to be the dominant source of new sulfate far offshore, dominating SO 2 entrainment from the free troposphere in some cases.

31 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Aerosol-Cloud-Precipitation Hypothesis #4: Depletion of aerosols by coalescence scavenging is necessary for the maintenance of POCs. Synthesis: All POCs exhibited much lower CCN concentrations than in the surrounding regions, and air exiting from their cloudly updrafts was often observed to be nearly entirely cleansed of all condensation nuclei of any size.

32 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Coupled Ocean-Atmosphere-Land Hypothesis #1: Oceanic mesoscale eddies play a major role in the transport of heat and fresh water from coastally upwelled water to regions further offshore. Synthesis: Oceanic mesoscale eddies were surveyed. Work with very high resolution coupled GCMs supports this hypothesis. Detailed comparisons of observations and simulations are under way.

33 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Coupled Ocean-Atmosphere-Land Hypothesis #2: By changing the physical and chemical properties of the upper ocean, upwelling has a systematic and noticeable effect on aerosol precursor gases and the aerosol size distribution over the SEP. Synthesis: DMS concentrations were not strongly elevated near the coastal upwelling zone. However, photochemical destruction of DMS seemed to be dominant source of new sulfate far offshore, dominating SO 2 entrainment from the free troposphere. Analysis of oceanic photochemical DMS destruction observations is under way.

34 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Coupled Ocean-Atmosphere-Land Hypothesis #3: The diurnal subsidence wave ( upsidence wave ) originating in northern Chile/southern Peru has an impact upon the diurnal cycle of clouds that is wellrepresented in numerical models. Synthesis: A detailed examination of ship radiosondes and prevoca/voca model output is under way.

35 Preliminary Confrontation of VOCALS Hypotheses with Rex Observations Coupled Ocean-Atmosphere-Land Hypothesis #4: The entrainment of cool fresh intermediate water from below the surface layer during mixing associated with energetic near-inertial oscillations generated by transients in the magnitude of the trade winds is an important process to maintain heat and salt balance of the surface layer of the ocean in the SEP. Synthesis: No progress reported so far.