1. New global short-wave radiation climatology from VOS data based on highly accurate parameterization:
interannual variability and the impact of cloud cover
Marina Aleksandrova Alexey Sinitsyn, Sergey Gulev
P.P. Shirshov Institute Of Oceanology, Moscow
OUTLINE
Existing SW parameterizations are based on total cloud cover
Application to VOS observations (1950-onwards).
Need for the new parameterization
Different cloud types imply strongly varying atmospheric transmission
New climatology of short-wave radiation

2. Data to develop parameterization
I. NEW PARAMETERIZATION
Data to develop parameterization
140 days of SW observation with 10-sec resolution
1500 hourly averages of SW radiation flux
simultaneous hourly observation of standard meteorological variables
Kipp&Zonen CNR-1
Spectral range for SW (pyranometr) 0,3-3 µm
Spectral range for infrared radiation
(pyrgeometr) µm
Range of view ≈180⁰
Temporal resolution sec
Accuracy (daily totals) ±10%

3. Clear sky conditions: Log-function instead of linear one
Okta, CL 1 2 3 4 5 6 7 8 ai
0.81
0.80
0.78
0.76
0.74
0.71
0.67
0.60
0.31 bi
0.15
0.13
0.17
0.14
0.12

4. Different cloud categories under 7-8 okta
Separate equations for different cloud types
8 octa - Ns
8 octa - Cs №
Category
Atm. transmission 1
Ns(7/0_2_X)
T=0,14 x sinh +0,11 2
Sc(Cu) (4_0_0)
T=0,33 x sinh +0,17 3
AsAc(0_7_X)
T=0,34 x sinh +0,19 4
Sc(no_Cu) (5_0_0_Sun1/0)
T=0,31 x sinh +0,22 5
Sc(no_Cu) (5_0_0_Sun_П)
T=0,25 x sinh +0,11
360 W/m2
620 W/m2
Dependence of transmission factor
on cloud types
Common for 8 okta
1 category
2 category
3 category
4 category
5 category
Comparison with alternative parameterization
implies better accuracy
Parameterization
Correlation
RMS error, W/m2
Dobson&Smith
0,97 81
MGO – total cloud cover
0,95 91
MGO – total + low cloud cover
0,96 88
New parameterizaton
0,98 53

5. New parameterization has been applied to VOS observation.
II. APPLICATION OF NEW PARAMETERIZATION AND DEVELOPMENT OF SW CLIMATOLOGY
New parameterization has been applied to VOS observation.
This dataset characterized by strong inhomogeneity of sampling in space and in time.
Number of observation per month
Spatial distribution of the VOS reports containing total cloud cover for December
Field production:
Spatially varying grid (2×2 to 4×10 cells)
Rotating local time around the clock (to allow for the use hourly models)
Objective interpolation (method of local procedures)

6. New global climatology of SW radiation
Month
Latitude
W/m2
Seasonal variation of zonally averaged SW radiation, W/m2

7. Comparison with the alternative hourly models

8. Comparison with alternative hourly models
Month
Global estimates of insolation
Dobson – New par.
MGO2 – New par.

9. Example of cloud distribution over the North Atlantic
December
June
December
June
December
June
December
June

10. Interannual variability of shortwave radiation and cloud cover over the North Atlantic
SW, W/m2
SW, W/m2
Cloud, okta
Cloud, okta
Year
Year
SW, W/m2
SW, W/m2
Cloud, okta
Cloud, okta
Linear trends
Year
Year
December
July
0-60⁰ N
20⁰-50⁰ N
SW Dobson
-0.64
-0.38
-1.17
-1.16
SW GGO
-0.66
-1.34
-1.50
SW new par.
-0.69
-0.39
-1.47
-1.68
Total cloud
0.038
0.027
0.066
0.077
Low clowd
0.013
0.008
0.067
0.079

11. CONCLUSIONS
New highly accurate parameterization  accounting for cloud types and non-linearity under clear skies
2. New global climatology of SW radiation flux (1950 – onwards)  significant differences with alternative hourly parameterizations
3. SW radiation flux over the North Atlantic is decreasing and cloud amount is increasing.
Interannual variability shows that during last 62 years incoming SW radiation over the North Atlantic is decreasing and amount of cloud is increasing.
To do:
To analyze potential links of the variability patterns to the cloud regimes in different regions of the ocean with incoming SW radiation.
Contacts:
Marina Aleksandrova