the impact of solar cycle on the dry sand skin temperature at ponce de leon beach

The impact of solar cycle on the dry sand

skin temperature at Ponce de Leon Beach

Jeremy Fimat

Motivations

• Skin temperature (Ts) is important to remote sensing (satellite).

• Ts connected to airflow in dune environment through radiative fluxes (energy budget).

• Fluxes impact the wind flow and atmospheric stability.

• Biological effects: Turtles hatchlings.

“The Denuded Beach”

Transect

From water’s edge to dune crest (East-to-West)

Methods• Skin temperature measured with an IR

thermometer.• Every 3 feet.

When

• Data collected over two days and two different periods of the day:- 23 June 2010: 10am – 3pm

6 transects.- 30 June 2010: 6pm – 9pm

3 transects.

ZONE 2 ZONE 1ZONE 3 ZONE 0

Wet sandDamp sand“Beach”: Dry sand

The 4 zones of the transect / 23 June

Dune

Transect

8am 4pm 12am

Sand temperature diurnal variation

R.J. Stathers, June 1984Time1pm 9pm

D

ry sa

nd te

mpe

ratu

re (

C)

• Surface energy budget: energy balance under ideal conditions (e.g., clear sky).

• 4 energy fluxes at skin surface:– Rn: Net radiation= incoming – outgoing radiation– SH: Sensible heat (Air). – GH: Ground heat flux.– LH: Latent heat: water vapor flux.

Diurnal skin temperature changes (ΔT)

Responses

Surface Energy Budget: for dry sand in early-morning (8am)

Sand surface

Rn

SH

GH

Surface Energy Budget: for dry sand at mid-morning (10am)

Sand surface

Rn

SH

GH

Surface Energy Budget: for dry sand at solar peak (1pm-2pm)

Sand surface

Rn

SH

GH

Surface Energy Budget: for dry sand at mid-afternoon (3/4pm)

Sand surface

Rn

SH

GH

Surface Energy Budget: for dry sand in early evening (6pm)

Sand surface

Rn SH

GH

Surface Energy Budget: for dry sand in late evening (9pm)

Sand surface

RnSH

GH

Expectations for ΔT

• ΔT = T an hour – T at the previous hour.• ΔT>0 = warming.• ΔT<0 = cooling.• An important ΔT in early morning (10am).• ΔT decreasing until solar peak.• ΔT = 0 in early afternoon.• ΔT increasing until sunset (9pm).

Local solar radiation on 23 June 2010

2:30 PM

1 PM

ZONE 2 ZONE 1ZONE 3 ZONE 0

Wet sandDamp sand“Beach”: Dry sand

The 4 zones of the transect / 23 June

Dune

Transect

The Beach Zone: ZONE 2 / 23 June

ZONE 2 ZONE 1ZONE 3 ZONE 0

Wet sandDamp sand“Beach”: Dry sand

The 4 zones of the transect / 30 June

Dune

Transect

The Beach Zone: ZONE 2 / 30 June

Observed ΔT with timeBeach Zone (ZONE 2)

Decreased warming: ΔT less positive.

Increased cooling: ΔT more negative.

Average ΔT = +8.3 FAverage ΔT = +6 F

Average ΔT = +3.3 FAverage ΔT = +0.4 F

Average ΔT = -9.5 F

Average ΔT = -11.4 F

Elevation sun angle with time

Sunrise Sunset

ΔT > 0 : Warming ΔT < 0 : Cooling

Decreased warmingIncreased cooling

• Maximum warming rate during mid-morning.• Maximum cooling rate during the evening.• Equilibrium after solar peak.• Dry sand skin temperature is correlated to

slope of solar elevation angle.• Governed by surface energy budget.

Conclusion/Summary: Dry sand / Beach Zone (ZONE 2)

Questions ? Next: Erik Mackay