Direct Measurements of theSurface Energy Balance

on Lake Superior (and Huron)

Peter Blanken, University of Colorado, Boulder

Christopher Spence, Environment Canada, Saskatoon

Newell Hedstrom, Environment Canada, Saskatoon

Introduction Background Site Methods Results Summary

Why measure the surface energy balance?• Help understand impacts of climate change (e.g. ice conditions)• Help calibrate/validate models to improve forecasts• Connections to the hydrologic cycle: evaporation-lake water levels• Ecological connections: water temperature cycles and thermal structure

Objective?To make continuous, multi-year direct measurements of the surface energy balance on Lake Superior to improve our understanding of key physical processes

• fluctuating water levels (e.g. Marquette)

Introduction Background Site Methods Results Summary

Introduction Background Site Methods Results Summary

Stannard Rock:39 km nearest shore

Air temperature and humidity

Rain: total & rate

Wind speed & direction

Latent, sensible,CO2, momentumfluxes; atm pressure, [H2O], [CO2 ]

Water surface temperature

Incident short- & long-wave radiation

Radio communication

• instrumentation

Introduction Background Site Methods Results Summary

32.4 m above mean water surface

0.5-hr means June 2008-March 2011

80% Turbulent Flux within 5.7 km

Greatest Sensitivity at

632 m

Not to Scale

• Turbulent Flux Footprint

Introduction Background Site Methods Results Summary

Short-wave Long-wave Radiation

NetRadiation

Turbulent Fluxes of Latent and Sensible

Heat

HeatStorage/Release

• radiation & energy balance

Introduction Background Site Methods Results Summary

SN JHLERLLSS

• eddy covariance

High-frequency vertical wind speed (w), & H2O / CO2 density (scalar s).

Covariance of deviation (′) from 30-min means (-).

Std. corrections.

swFluxs

Introduction Background Site Methods Results Summary

• wind rose

Introduction Background Site Methods Results Summary

2008-09

6%

4%

2%

WEST EAST

SOUTH

NORTH

5 - 10

10 - 15

15 - 20

20 - 25

25 - 30

30 - 35

35 - 40

40 - 45

2009-10

6%

4%

2%

WEST EAST

SOUTH

NORTH

5 - 10

10 - 15

15 - 20

20 - 25

25 - 30

30 - 35

Water Year Water Year

• wind direction and the energy balance

Introduction Background Site Methods Results Summary

20 40 60 80 100

30

210

60

240

90270

120

300

150

330

180

02008-09 Water Year

LE

H

20 40 60 80 100

30

210

60

240

90270

120

300

150

330

180

02009-10 Water Year

Rings : MeansW m-2

-15

0

15

30T

a (

oC

) Max 28.87

Min -16.31

0

1

2

3

ea (

kP

a)

Max 2.679

J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M0

20

40

U (

m s

-1)

Max 42.73

Month

• 0.5-hr basic meteorology with 10-day running mean

Introduction Background Site Methods Results Summary

2009 2010 2011

0

500

1000

RN (

W m

-2)

-200

0

300

600

LE

(W

m-2

)

-200

0

300

600

H (

W m

-2)

J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M

-750

0

750

J S (

W m

-2)

Month

• 0.5-hr energy balance with 10-day running mean

Introduction Background Site Methods Results Summary

2009 2010 2011

0

200

400

Measured

LE=mU+k

0

200

400

LE

(W

m-2

)

Measured

LE=U(m*ea+k)

Dec 29 Dec 31 Jan 2 Jan 4 Jan 6 Jan 8 Jan 10 Jan 12 Jan 140

200

400

Measured

LE=m*U/ea+k

• LE calculations

Introduction Background Site Methods Results Summary

2010 2011

• cumulative heat losses

Introduction Background Site Methods Results Summary

0

400

800

2008-09: 464 mm

2009-10: 645 mm

O N D J F M A M J J A S0

200

400

Month

Cum

ula

tive T

ota

l (m

m e

quiv

ale

nt)

2008-09: 374 mm

2009-10: 345 mm

Sensible Heat

Evaporation

• ice conditions

Introduction Background Site Methods Results Summary

March 3, 2009: 92% max

March 5, 2010:28% max

• Lake Huron: Spectacle Reef

Introduction Background Site Methods Results Summary

Introduction Background Site Methods Results Summary

Stannard Rock:

Spectacle Reef:17 km nearest shore

• basic meteorology: 24-hr means Superior vs Huron

Introduction Background Site Methods Results Summary

-15

0

15

30

Ta (

oC

)

0

1

2

3

ea (

kP

a)

Superior

Huron

O N D J F M A M J J A S0

5

10

15

U (

m s

-1)

Month

Time Lag for Maximum Correlation (Huron after Superior) :

Ta: 21 hrsea: 17 hrsU: 19 hrs

• energy balance: 24-hr means Superior vs Huron

Introduction Background Site Methods Results Summary

0

200

400

Rn (

W m

-2)

0

200

400

LE

(W

m-2

)

0

200

400

H (

W m

-2)

O N D J F M A M J J A S-800

-400

0

400

Js (

W m

-2)

Month

Superior

HuronTime Lag for Maximum Correlation (Huron after Superior) :

LE: 19 hrsH: 17 hrs

0

400

800

Superior: 586 mm

Huron: 584 mm

O N D J F M A M J J A S0

400

800

Month (2009-2010)

Cum

ula

tive (

mm

equiv

ale

nt)

Superior: 347 mm

Huron: 367 mm

• cumulative heat loss

Introduction Background Site Methods Results Summary

90 mm (15%)

Evaporation

Sensible Heat

Introduction Background Site Methods Results Summary

1. Annual Cycles:• Summer is the time for energy input (net radiation = heat storage); winter

is the time for energy output (heat storage = latent + sensible heat ) with a 5-month lag

• ~500-600 mm annual water level drop due to evaporation; ~ 200 mm difference between years

• Evaporation and sensible heat losses greater over Huron than Superior, yet meteorological conditions similar (20-hr delay)

2. Processes: • Evaporation and sensible heat losses occurred over 2-3 day-long events,

proportional to horizontal wind speed; inversely proportional to vapor pressure

3. Lake Water Levels: • Does a greater heat loss (latent and sensible heat) result in sufficient lake

temperature decrease to promote ice formation, thus reduce the next summer’s heat storage, thus reduce the next winter’s evaporation?

Direct Measurements of theSurface Energy Balance

on Lake SuperiorPeter Blanken, University of Colorado, Boulder

Christopher Spence, Environment Canada, Saskatoon

Newell Hedstrom, Environment Canada, Saskatoon

GLLKA