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