1. LAND TEAM. GOES-R AWG Annual Meeting. June 14-16, 2011
LAND TEAM GOES-R AWG Annual Meeting. June 14-16, Fort Collins, CO
LAND SURFACE AND AIR TEMPERATURE (LST & SAT) AT CLEAR AND OVERCAST SKIES
Konstantin Y. Vinnikov (University of Maryland), Yunyue Yu (NOAA/NESDIS), Mitchell D. Goldberg (NOAA/NESDIS)
Dan Tarpley (Short & Associates), Ming Chen (IMSG), Chuck N. Long (PNNL)
Statistical analysis of multiyear records of LST & SAT observed at six US SURFRAD stations
LST & SAT at OVC sky conditions
LST & SAT at ALL sky conditions
LST & SAT at CLR sky conditions
OCCURRENCE OF CLR & OVC SKIES
STATISTICAL DISTRIBUTION OF CLOUDINESS
CLR-clear sky. (Fractional amount) = 0.
OVC-overcast sky. (Fractional amount) ≥ 0.9.
OTHER skies. 0 < (Fractional amount) ≤ 0.9.
“Bin averaging” technique.
Bin size= 1 hour x 1 month.
LST –Land Surface Temperature;
SAT- Surface Air Temperature;
ALL sky conditions (CLR & OVC & OTHER).
“Bin averaging” technique is applied to estimate Expected Value and Standard Deviation of LST and SAT at each 1 hour x 1 month bin.
LST –Land Surface Temperature;
SAT- Surface Air Temperature;
OVC - Overcast sky conditions.
“Bin averaging” technique.
LST –Land Surface Temperature;
SAT- Surface Air Temperature;
CLR - Clear sky conditions.
“Bin averaging” technique.
For small pixels fractional amount of total cloudiness has a U-shaped statistical distribution with much larger occurrences of CLR and OVC sky conditions compared to other fractional amounts of cloudiness. Generally, CLR sky takes place in about 1/3 of all observations with relatively small diurnal/seasonal variations.
CLR sky occurrence is smaller during the spring/summer months with early afternoon minimum, and larger - in the autumn. At the Desert Rock, NV station clear sky conditions prevail because of very dry regional climate.
OVC sky occurrence has daytime maximum in the diurnal cycle and winter maximum in the seasonal cycle.
Most of the selected stations display a sharp decreasing of OVC sky occurrence at sunset and a sharp increasing – at sunrise.
Occurrence of the “OTHER” fractional cloudiness, other than CLR and OVC, is also about 1/3 of all observations but it is largest during warm season with morning maximum that usually exceeds 50%.
At CLR sky, diurnal and seasonal amplitudes of LST are significantly larger than those of SAT.
Annual cycle of standard deviations of LST and SAT have summer minimum and cold season maximum.
Diurnal cycle of LST has a maximum close to noon time.
Maximum in diurnal cycle of SAT is shifted to ~3p.m. local solar time.
Standard deviations of LST are very close to those of SAT.
At OVC sky, diurnal and seasonal amplitudes of LST are noticeably larger than those of SAT.
Annual cycles of standard deviations of LST and SAT have summer minimum and cold season maximum.
Diurnal cycle of LST has a maximum close to noon time.
Maximum in diurnal cycle of SAT is shifted to ~3p.m. of local solar time.
Standard deviations of LST are very close to those of SAT.
LST and SAT, display regular seasonal and diurnal cycles in the expected value with significantly larger amplitudes for LST compared to SAT
The annual cycle of standard deviations of LST and SAT have a summer minimum. Cold season maximum is shifted to the spring.
The diurnal cycle of LST has a maximum close to noon time.
The maximum in diurnal cycle of SAT is shifted to ~3p.m. local solar time.
Standard deviations of LST are only a little larger than those of SAT.
ANNUAL AVERAGES OF LST & SAT
CLR & OVC SKIES DIFFERENCES <LST-SAT>
LST & SAT DIFFERENCES AT CLR & OVC
LST & SAT CORRELATIONS AT LAG=0 .
Estimates of the systematic difference <LST-SAT> are statistically significant for ALL, CLR & OVC sky conditions.
Daytime differences are much larger at CLR than at OVC skies.
Nighttime <LST-SAT> differences are close to ZERO at OVC sky, and they are about -2 to -4°C at CLR sky conditions.
At CLR sky , the systematic <LST-SAT> differences are mostly larger than their standard deviations.
At OVC sky, this systematic differences have the same order of value as their SD- standard deviations.
Sensitivity of LST and SAT to changes in Cloudiness.
“Bin averaging technique” estimates of mean differences of <LST> or <SAT> at CLR and OVC skies :
<LSTclr>-<LSTovc> & <SATclr>-<SATovc>.
Daytime LST increases with decrease of cloudiness.
Nighttime LST is decreases with decrease of cloudiness.
LST is almost twice as sensitive to change in cloudiness compared to SAT.
<LSTclr-LSTovc> is almost mirror symmetric to noon time in the diurnal cycle. (Does it mean that thermal inertia of the vegetated “Land Surface” is negligibly small?)
<SATclr-SATovc> is almost mirror symmetric to ~3 p.m. time in the diurnal cycle. (Is it shifted because of thermal inertia of surface air layer?)
Values |<LSTclr-LSTovc>|>2°C & |<SATclr-SATovc>|>2°C are statistically significant.
Standard Deviations of LST & SAT (ºC) and
their Lag=0 X-Correlation Coefficients
for ALL, CLR, and OVC Skies
Annual Averages of LST, SAT and their Differences
for ALL, CLR, & OVC Skies, ºC.
ALL
CLR
OVC
LST
SAT
Diff
FPK
6.5
5.7
0.8
6.6
5.9
0.7
5.5
4.5
1.0
SXF
8.2
7.9
0.3
7.5
0.0
7.4
PSU
9.7
9.8
-0.1
8.0
8.6
-0.5
10.1
BON
10.8
11.2
-0.4
9.1
10.0
-0.9
11.1
DRA
20.3
18.3
1.9
20.6
18.6
2.0
17.8
16.2
1.6
GWN
16.9
16.7
0.2
15.2
15.1
0.1
16.4
0.5
0≤ALL≤1
CLR=0
OVC≥0.9
0<OTHER<0.9
σLST ºC
σSAT
Lag=0
CORR
FPK
6.6
6.4
0.93
6.7
0.92
5.6
5.7
0.95
6.1
6.3
SXF
5.5
5.4
4.5
4.8
0.97
0.94
PSU
5.3
5.1
4.7
4.9
4.2
0.96
BON
5.0
DRA
4.0
0.90
3.6
3.9
4.3
GWN
0.91
4.1
The Differences of Annual Means <LST-SAT> at ALL, CLR & OVC skies.
The Differences of <LST> or <SAT> at CLR and OVC, ALL and CLR, ALL and OVC skies are relatively small and do not exceed 2°C at the most of the SURFRAD stations.
Lag=0 correlation between LST and SAT is very stable and is the largest at OVC sky conditions.
Standard Deviations of LST and SAT at ALL, CLR, OVC, and OTHER skies are very close between themselves.
LAG-CORRELATION of LST & SAT
CROSS-LAG-CORRELATION of LST & SAT
CONCLUSIONS
Your Questions should be addressed to:
Expected values of LST and SAT display strong diurnal and seasonal variations. They are significantly different at CLR and OVC sky conditions.
LST at CLR sky is warmer than at OVC sky at daytime and it is colder at nighttime. The same is true for SAT.
LST is warmer than SAT at daytime and colder than SAT at nighttime at CLR, OVC and ALL skies.
Scales of lag-correlation and cross-lag-correlation of LST and SAT are almost the same at CLR, OVC and ALL skies.
Moving mid-latitudinal weather systems are responsible for temporal variability of LST and SAT.
At arbitrary sky conditions, the observed temporal variations of LST and SAT carry the same weather-related signal.
Communicating author: Konstantin Vinnikov, University of Maryland, Department of Atmospheric and Oceanic Science, College Park, MD
Phone:
Related publications:
Konstantin Y. Vinnikov, Yunyue Yu, M. K. Rama Varma Raja, Dan Tarpley, Mitchell D. Goldberg, 2008: Diurnal-Seasonal and Weather-Related Variations of Land Surface Temperature Observed from Geostationary Satellites. Geophysical Research Letters, 35, doi: /2008GL
Konstantin Y. Vinnikov, Yunue Yu, Mitchell D. Goldberg, Ming Chen, and Dan Tarpley, 2011: Scales of temporal and spatial variability of midlatitude land surface temperature. J. Geophys. Res., 116, doi: /2010JD
Empirical estimates of
LAG-CORRELATION FUNCTIONS of time series of standardized anomalies of LST (BLUE lines) and SAT (RED lines):
F(t) is LST or SAT, t is time.
is time
dependent Expected value of F(t).
F’(t)=F(t)-E[F(t)] is anomaly;
θ(t)=F’(t)/σF (t) is standardized anomaly.
is lag-correlation, τ is Lag.
Synoptic scale temporal variations prevail in lag-correlation functions of LST and SAT at ALL, CLR, & OVC skies.
Larger-scale, interseasonal to interdecadal, temporal variability of LST and SAT are much weaker compared to the synoptic-scale component. There is no statistically significant lag-correlation for lags above two weeks.
Empirical Estimates of CROSS-LAG-CORRELATION FUNCTIONS of LST and SAT at ALL, CLR, & OVC skies:
There is no significant difference between scales of temporal variability (autocorrelation) of LST and SAT.
The scales are the same at CLR, OVC, & ALL sky conditions.
Temporal variations of LST and SAT are modulated by the same synoptic-scale weather processes and closely correlated.