Squall Lines moving over Santarem

Julia Cohen Federal University of Para, Brazil

David FitzjarraldAtmospheric Sciences Research Center/ University at Albany, USA

Wet season

Fitzjarrald et al, 2008

Squall Lines initiated by the sea breeze

Squall Lines initiated by the sea breeze

Squall Lines initiated by the sea breeze

Squall Lines initiated by the sea breeze

Squall Lines initiated by the sea breeze

Mean feature of the Squall Lines(1979 to 1986)

CLASSIFICATION• Coastal Squall Line (CSL) = moves no more 170km.• Squall Line type 1 (SL1) = moves 170 and 400 km inland.• Squall Line type 2 (SL2) = moves more than 400 km inland.

• Max Occurrence May and August.

• mean length = 1400 km.• mean width = 170km.

• Average propagation speed = 12 and 16 m/s.• life time: 9, 12 and 16 hours.

00-03 UTC

00-03 UTC

06-09 UTC06-09

UTC 12-15 UTC

12-15 UTC

18-21 UTC

18-21 UTC

(From Kousky et al. 2006, CMORPH analyses)

Influence of large scale ‘mega squall lines’ on precipitation

Time of ‘maximum precipitation rate’

Fitzjarrald et al, 2008

Objective

The precipitation climatology of eastern Amazon reflects the relative importance of locally forced convective rain and instability line rainfall. (near Santarém these splits out by time of day).

Numerical simulations of instability lines to describe instability line rainfall component.

Climatology • Imagery satellite (2000 to 2006)• CSL propagating < 140 km• SL1 propagating 140 to 400km• SL2 propagating > 400km• CMORPH (0.25o) – 00 to 09UTC (Dec 2002 to

December 2006);• Reanalyses CPTEC-ETA (40km) – (2000 to 2004).

Analyse the contribution of the rain generated by squall lines when passing Santarem region.

Monthly distribution of the number of squall lines during 2000 to 2006

SLC propagated < 140 km ( stippled)SL1 propagated 140 to 400 km (white) SL2 propagated > 400 km (black)SL2 propagated > 400 km and moved over Santarem (gray)

CMORPH composite rainfall totals for storms between 00 to 09UTC 12/1/02 – 12/31/06

Propagated past Santarem Not propagated deeply into the Basin

Branch north has more rainfall than branch south.Less rainfall in confluence Tapajos and Amazonas River.

SLC (fine line)SL1 (short dashed line)SL2 (heavy continuous line)SL2 over Santarém (long dashed line)

Numerical Experiment Description

• BRAMS = Brazilian developments on the Regional Atmospheric (RAMS) (Cotton et al., 2003).

• The model’s initialization was variable, each 6 hours, with the analysis of CPTEC’s global model, the radiosondes and the available surface data.

• The integration period was 36 hours, initiating on June, 02, 2006, at 12 UTC.

• Models of surface and vegetation, radiation, Cloud microphysics.

• Grell’s deep convective parameterization and shallow convection parameterization.

• Control and Topography Experiments.

3 Grids • Points X = 82,113,140

• Points Y = 60,89,113

• Points Z = 27,27,27

• Points in soil = 8

Grid increments ( 72 , 24, 8 km) River and Topography (m)

Grid 2 Grid 3

(included June, 03 04UTC)

Satellity Infra-Red Cannel and Rate Precipitation (mm/h) by BRAMS

June 02 2006 16 UTC

Grid 2 (24 km)

June,03 2006 08 UTC

Grid 3 (8 km)

Data = Vila Franca (2.34S, 55.02W)Model = (2.63S 54.5W)

Grid 2

Fitzjarrald et al, 2008

Macapa – Close coastal Santarem

Grid 2

June, 02 18 UTC June, 03 06UTC

Vertical wind (cm/s) and Mixture rate all condensate

June, 03 2006 08 UTC

Grid 3

Control (with topography) Test (without topography)

Grid 3 - 0.6 SControl (with topography) Test (without topography)

CONCLUSIONS

• Even weak topography is important to squall propagation speed and rainfall intensity at STM.

• Weak meridional jet associated with inland propagation.

• Gravity waves trail the squall and may influence how far the squall propagates into the continent.

• Case study precipitation agrees with observations at Vila Franca (confluence ‘lake’) both in rainfall total and rainfall timing.

Future studies• Case studies for only local convective rain.• Composite rainfall transects normal to

Amazon (CMORPH, reanalysis, BRAMS).• Soil moisture ‘memory’ and squall line

propagation.• Role of trailing gravity waves in squall wake.• Role of river water temperature on regional

convection.