The impact of solar cycle on the dry sand skin temperature at Ponce de Leon Beach Jeremy Fimat

Motivations Skin temperature (T s ) is important to remote sensing (satellite). T s 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 June 2010: 6pm – 9pm  3 transects.

ZONE 2ZONE 1ZONE 3ZONE 0 Wet sand Damp 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 1984 Time 1pm9pm Dry sand temperature ( ̊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 Rn SH 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 :30 PM 1 PM

ZONE 2ZONE 1ZONE 3ZONE 0 Wet sand Damp sand“Beach”: Dry sand The 4 zones of the transect / 23 June Dune Transect

The Beach Zone: ZONE 2 / 23 June

ZONE 2ZONE 1ZONE 3ZONE 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 time Beach Zone (ZONE 2) Decreased warming: ΔT less positive. Increased cooling: ΔT more negative.

Average ΔT = +8.3 ̊F Average ΔT = +6 ̊F Average ΔT = +3.3 ̊F Average ΔT = +0.4 ̊F Average ΔT = -9.5 ̊F Average ΔT = ̊F Elevation sun angle with time SunriseSunset ΔT > 0 : WarmingΔT < 0 : Cooling Decreased warming Increased 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