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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 s
and
tem
pera
ture
( ̊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