Mesoscale environments related to precipitation extremes and severe events in convective situations over SESA, their simulation with high resolution models. Matilde Nicolini, Yanina García Skabar and Paola Salio CIMA-DCAO-CONICET-UBA- SMN
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Mesoscale environments related to precipitation extremes and severe events in convective situations over SESA, their simulation with high resolution models.
Yanina García Skabar and Paola Salio
2ND MEETING OF IFAECI (UMI 3351) Buenos Aires. Argentina
Current Objectives: severe events in convective situations over SESA, their simulation with high resolution models
investigate the mechanisms controlling deep moist convection in the north-central domain of Argentina and to focus on short range prediction of these mechanisms.
improve short range mesoscale numerical prediction with emphasis in different forcings of convection, from two different strategies: an explicit deterministic prediction of convection with high resolution and an ensemble forecast that allows a probabilistic approach.
Diurnal cycle in convergence patterns in the boundary layer east of the Andes and convection
To progress in the study of the mechanisms that control the diurnal cycle of precipitation and convection in subtropical latitudes east of the Andes during summer
If nocturnal convergence in the boundary layer exists over the broad valleys east of the Andes then it may be efficient in triggering or intensifying deep moist convection -that may have started earlier during the afternoon if moisture is available and conditional instability prevails-.
Methodology: east of the Andes and convection
SALLJEX was performed in Southeastern South America from November 15, 2002 to February 15, 2003 to monitor, quantify and analyze the low-level circulation over this region and its related precipitation. Enriched analyses were generated ingesting all available data with a higher spatial and temporal resolution than that available for the region, following a downscaling methodology, using Brazilian Regional Atmospheric Modeling System (BRAMS, www.brams.cptec.inpe.br).
To identify the convective systems and their life cycle IR brightness temperature data was employed at half hourly intervals with a horizontal resolution of 4km over the area between 10ºS-40ºS and 40ºW- 75ºW, data online at http://lake.nascom.nasa.gov/).
The present study is organized around a two weeks long period (since January 24 up to February 7/2003) during SALLJEX that followed a cold incursion and during which different environmental conditions prevailed.
BRAMS was applied to obtain analysis every three hours, with a horizontal resolution of 80 km covering mostly South America and an enhanced inner domain with 20 km resolution for the region encompassing Central and Northern Argentina, southern Brazil, Bolivia, Paraguay and Uruguay
Questions: east of the Andes and convection
¿Are the 20 km resolutionenriched analyses with SALLJEX data capable to reproduce a diurnal cycle of convergence/divergence and rising/subsiding motions at the top of the boundary layer, that may be related to a northwestern mountains-central plain flow regime?
¿To which extent these circulations are sufficient by themselves to support deep convection or else other ABL circulation patterns as the east of the Andes low-level jet are more effective depending on the synoptic situation?
The study period was characterized by two different main synoptic conditions:
January 24 to 30:persistent anticyclonic circulation(intensified South Atlantic Convergence Zone, SACZ) and a quasi-stationary front at the southern border of the domain. Subsidence and diabatic warming in the subtropical boundary layer favored relatively dry conditions over central Argentina.
January 31 to February 7: extreme heat wave with a weak SACZ and the presence of an intense thermal low over northwestern Argentina enhancing a northerly flow and coherently the presence of theeast of the Andes low-level jet (SALLJ). Warm and moist horizontal advection dominated over Argentina.
Anticyclonic situation synoptic conditions:
SALLJ dominated situation
During anticyclonic conditions synoptic conditions:
Average ABL conv/div in the area shows that mesoscale zonal circulations (mountain/broad plain) dominate over meridional circulations in the average total convergence values at night and divergence dominates in the afternoon.
Moisture and/or zonal convergence are not enough to support both nocturnal and daytime convection over the northern plains. Southward (35S), convection is triggered in the evening and intensified at night forced by a quasi-stationary frontal zone (not shown in the figures).
During strong and shifted to the south SALLJ synoptic conditions:
Average ABL conv/div in the area shows that meridional circulation (more efficient to advect moisture) dominates (over zonal circulations) convergence values at night while zonal circulation dominates the divergence in the afternoon over the plains.
Higher moisture values during this period and convergence related to a propagating frontal zone are efficient to trigger convection in the afternoonat 35S (even if mean zonal divergence dominates in the area). It propagates northward and intensifies during night in a domain dominated by meridional convergence related to the SALLJ.
Both the patterns of divergence related to ABL mesoscale circulations and deep convection present a nocturnal phase in their diurnal cycles.
Mesoscale circulations are altered once deep convective circulations dominate over the plains.
a) synoptic conditions:
Mesoscale circulations east of the Andes
Nicolini, M., Garcia Skabar, Y., (2010)
BRAMS 3.2 Brazilian Regional Atmospheric Modeling System version 3.2
Simulation period : March 2007 from 25 to 31 at 12UTC
Two-way grid interactive nesting technique
Number of atmospheric levels: 30;
vertical cordinate: shaved eta
Horizontal Resolution: Grid 1 - 50 km Grid 2 - 12.5 km, Grid 3 - 3.125 km
GDAS analyses from NOAA/NCEP as initial and boundary conditions.Model includes topography data (1km resolution)
terrain land use (1km resolution), soil types (50km resolution), weekly sea surface temperaturesdaily soil moisture heterogeneous fields from USP/CPTECParameterizations:
Shallow cumulus:Sousa and Silva;
Deep convection: Grell; Explicit convection on Grid 2 and 3
Radiative: Chen and Cotton;
Vertical diffusion: Mellor-Yamada;
Microphysics: 8 water species, bulk water scheme
To describe the synoptic and mesoscale environment with particular emphasis in the relationship convective precipitation/ LLJ.
To evaluate BRAMS performance in simulating an extreme rainfall situation
Observed precipitation over central Argentina, CMORPH (blue) and models forecast by (red and yellow) different grids accumulated between March 26 to 31, 2007. Grid 2 represents the precipitation forecast for 12.5 km and Grid 3 for 3.125 km respectively.
Synoptic Forcing (blue) and models forecast by (red and yellow) different grids accumulated between March 26 to 31, 2007. Grid 2 represents the precipitation forecast for 12.5 km and Grid 3 for 3.125 km respectively.
Meridional wind at 30S
Equivalent potential temperature
200 hPa Streamlines
and wind intensity
Vertically Integrated Moisture flux and its convergence
Temporal Evolution of GPS-Precipitable water (blue) and models forecast by (red and yellow) different grids accumulated between March 26 to 31, 2007. Grid 2 represents the precipitation forecast for 12.5 km and Grid 3 for 3.125 km respectively.
Convective and Stratiform Precipitation estimated by the CMORPH and IR area and the relationship with the LLJ
Stratiform and convective estimated precipitation for all systems that affect the central region of Argentina between March 25 to April 1, 2007 (green and purple). Meridional wind at 30ºS averaged between 63 and 58ºW and its ageostrophic component (pink and blue respectively) calculated from grid 3.
To progress in theforecast of MCS events and specifically to evaluate the performance of BRAMS forecast andstudy the sensitivityto different initial conditions, horizontal and vertical resolution and settings on cloud microphysics schemein a pre-frontal squall line event.
During early morning of January 12, 2010 an extended convective line developed in association with a cold front that propagated over the central and northern part of Buenos Aires Province, Argentina.
Methodology: CMORPH and IR area and the relationship with the LLJ
following Walko et al, 1995.
setting at National Weather Service
from 18 UTC to 12 UTC of next day
initialized with a 6 hours ETA model forecast
Comparison against radar data squall line reflectivity evolution at 3 KM.
Ensemble FCST 07 Ezeiza Radar
All forecasts present a squall line reflectivity pattern similar to radar observations but forecasts depict larger reflectivity values, compared with Ezeiza radar that has a tendency to underestimation.
Comparison against CMORPH estimations evolution at 3 KM.
8KM 30 min resolution
Area with accumulated precipitation >15mm/30min
Comparison against disdrometer accumulative Precipitation 10 min
Surface automatic stations Precipitation 10 min
Pergamino San Pedro Boedo-Bs.As.
10min acc. Precipitation
Wind Speed 10m
10min acc. Precipitation
Wind Speed 10m
Case studies approach
CHUVA Project Precipitation 10 min
Leader: Luiz Agusto Toledo Machado
Sites for the field campaign
New experiment at Foz de Iguazu
From 10-2012 to 1-2013
Cloud processes of tHe main precipitation systems in Brazil: A contribUtion to cloud resolVing modeling and to the GPM (GlobAl Precipitation Measurement)
Scientific questions: Precipitation 10 min
How to estimate rainfall from warm and deep clouds?
What is the contribution of rain from warm clouds to the total precipitation in different regions of Brazil?
How to improve both space and time precipitation estimation of rainfall over the continent for the GPM constellation?
What are the average characteristics (3D - cloud processes) of the main regimes of precipitation in Brazil?
What is the contribution of the aerosol in the process of formation of precipitation?
What are the main surface and boundary layer processes in the formation and maintenance of clouds?
How cloud microphysics and electrification processes evolves during the cloud life cycle?
How to improve precipitation estimation and cloud microphysics description by using conventional and polarimetric radar?
4.2 INSTRUMENTATION PACK Precipitation 10 min
The following instruments will compose the typical instrumentation pack to be used in the field
1. Dual Polarization Doppler X band radar (see figure 4)
2. EZ Lidar ALS450 (see Figure 4)
3. Microwave Radiometer MP3000 (see Figure 4)
4. 6 Laser Disdrometer (Figure 5)
5. 3 Meteorological Surface Stations
6. 2 Field Mill - Campbell
7. Radiosonde RS-92
8. Turbulent fluxes of heat and moisture
9. GPS Station
10. Soil Moisture
11. Airplane equipped with cloud microphysical instrumentation (only some campaigns)
12. Rain gauges
13. CCD cameras
14. Vertical pointing radar – micro rain radar (Figure 6)
15. Low-light Level CCD cameras
Satellites images: NOAA, TRMM, Megha-Tropique, AQUA, GOES and MSG
Radiosondes from Brazilian network
Surface Station (raingauge)
Brasildat network - Brazilian lightning detection network): http://www.rindat.com.br
STARNET (South American lightning network) - http://www.zeus.iag.usp.br
At some sites the basic pack information will be complemented by others instruments available like
X Band dual polarization and Doppler radar (Alcântara)
1S-Band Doppler radar (Belém, Manaus, Curitiba, São Roque, Pelotas and Fortaleza)
Micrometeorological Tower (Maranhão- Amazonas – Santa Maria) 4
San Luis Precipitation 10 min
Salto Grande –
Probability Density Functions
Probability Density Functions
Results Precipitation 10 min
Vertical cross section of potential temperature wind barbs and meridional component of the wind at 25°S. All panels cover a longitudinal range from 65°W to 54°W, at 3 h apart
Borque et al., 2010, Wea. and For. Vol. 25, 3970–986