Chuliang Xiao1 and Brent Lofgren2 1CILER , University of Michigan2NOAA GLERL

A Study of Great Lakes Effects on Synoptic Processes by Using WRF

Comparison Experiments

The Great Lakes Operational Meteorology Workshop 2014

Ann Arbor, MI

Outline

• Synoptic Overviews• Data and Model• Results from Model Comparisons• Conclusions

Outline

• Synoptic Overviews– Low Patterns– Low Tracks

• Data and Model• Results from Model Comparisons• Conclusions

Synoptic Map (Deep Low)17Nov2013 18Nov2013

Midwest Tornados outbreak

Courtesy http://www.hpc.ncep.noaa.gov/dailywxmap/

Synoptic Map (Shallow Low)14Dec2013 15Dec2013

East-coast Snowstorm outbreak

Courtesy http://www.hpc.ncep.noaa.gov/dailywxmap/

Outlines and Centers992 hPa

1012 hPa

Outline

• Synoptic Overviews• Data and Model– Datasets (NCEP Eta, FNL, SST, Station)– Model description– Experimental designs

• Results from Model Comparisons• Conclusions

Datasets

• NCEP Eta (6 hourly, 40 km, North America)• NCEP FNL (6 hourly, ~100 km, Global) (for comparison with NCEP Eta)

• NCEP RTG SST (Daily, HR, ~ 8 Km, Global)• MODIS (20-cat. Land Use; 16-cat. Soil; Collected in 2001)• Gauged Precipitation (Great Lake area)

Datasets (Cont.)Dataset NCEP Eta NCEP FNL RTG SST

Resolution 40 km 1*1 degree 1/12 degree

6 hourly 6 hourly Daily

Format GRIB 2 GRIB 2 GRIB 1

Provider NCEP Eta 212 grid NCEP GFS NCEP MMAB

WRF (Version 3.5.1) Domain

Projection Lambert

True latitudes 30°N, 60°N

Reference Latitude 45°N

Reference Longitude 85°W

Analysis field NCEP Eta (40 km x 40 km)

Domain Resolution 15 km x 15 km

Domain Mesh 100 x 142

Land Surface Model Noah LSM with MODIS 2001 (30”)

WRF Domain (Cont.)

Lakes-mean: Only lake gridsArea-mean: Red rectangle areaDomain-mean: ALL model grids

Experiment Comparison

Cases Deep Low Shallow Low

ExperimentIntegration Period (2013)

00Z16Nov~12Z19Nov 00Z13Dec~12Z16Dec

CONTROL MODIS, NCEP Eta

NOLakes Modifed Landuse+Vegetation+Soil, NCEP Eta

SSTLakes MODIS, NCEP Eta , Updated RTG SST

Landuse ModificationCONTROL NOLakes

Modification (Cont.)

Variable Description Variable Name CONTROL-

MODIS

NOLakes- Modified

Superior Others

Land use LU_INDEX Water Bodies (17) Mixed Forest (5) Cropland

(12)

Vegetation fraction VEGFRA 0% 20% 25%

Soil category fraction

SOILCTOP Water(14)

Sandy Loam(3)

Silt Loam(4)SOILCBOT

Modification (Cont.)

• The land use, vegetation and soil categories were specified differently between Lake Superior and the other four lakes.

• This allows small surface fluxes of heat and moisture to develop, but prevents any mechanical effects from discontinuities in surface roughness.

The lake surface and substrate temperature were also altered in Sousounis and Fritsch (1994).

Outline

• Synoptic Overviews• Data and Model• Results from Model Comparisons– Validation (Precipitation)– Storm Evolutions (SLP)– Surface process (Temperature, Moisture, Heat flux)– Vertical extent (local circulation)– Local circulation <-> background flow

• Conclusions

Model Validation (Precipitation)

NCEP Eta 40km

NCEP FNL 100km

CONTROL 15km

Observation

Deep Low Shallow Low

Storm Evolutions (Area-mean SLP)

Black: CONTRLRED: NOLakesBlue: SSTLakes

local time (EST)

The bottom bars are the differences

Deep Low

Shallow Low

Surface process (Temperature)

Lakes-Mean Surface Temp (TSK)

Area-MeanAir Temp at 2 m(T2)

Lakes-Mean TSK-T2

Black: CONTROLRED: NOLakesBlue: SSTLakes

local time (EST)

Lake temperature is not changed in the initial time, but got quick equilibrium in WRF-Noah

ColdLakes

Surface process (Humidity)

CONTROL

CONTROL-NOLakes

CONTROL-SSTLakes

Vector: (qu, qv)Shading: (qu, qv)∇q: mix ratio

Surface process (Sensible Heat)

Cross Sections992 hPa

1012 hPa

Dashed: Southwest-Northeast

Dot: Northwest-Southeast

Cross-sections

Shading: Temperature; Contour: Geopotential Height

NW-SE

SW-NE

Circulation Configuration

Vector: U, V at 10 mShading: T850Contour: Z500

CONTROL

CONTROL-NOLakes

CONTROL-SSTLakes

Conclusions

• WRF performs well in simulating both the deep low and shallow low.

• Lake-air temperature gradient induces vertical heat flux; lake-land roughness contrast contributes to moisture convergence.

• The Great Lakes’ effect generally strengthens the low system near the surface but is sensitive to the background flow.

• This effect becomes much more significant for the development of the shallow low and extends to a higher level, tilting downwind.

• The remote influence of the Great Lakes tends to be subtle in both cases.

THANK YOU