Modifications to the CERES TOASRB FM1 and FM2 Monthly Mean

In Spring 2007, the CERES TOASRB TOA fluxes were reprocessed from March 2000 to Oct 2005 for Terra and July 2002 to Oct 2005 for Aqua (where available) to correct for their 1) missing data, and 2) unrealistically large (~3 PW) global mean net flux imbalance and also, to fill in missing data.The adjustments made to adjust for the global imbalance have only been made at TOA. Surface fluxes have not been adjusted.

1) Missing Data: The missing data all occur for the Absorbed Solar Radiation (ASR) and thus net radiation near the delimiter of the incoming radiation where it is difficult to obtain an accurate albedo. To fill the missing data, we firstly took advantage of the fact that the areas missing varied from year to year and we formed a climatology of the available data on albedo. A least squares fitted first harmonic of the annual cycle was then derived for each point, and the missing climatological mean values determined and these were used to fill in the missing albedo. Interpolated values of albedo were constrainted not to exceed unity. The ASR and net radiation were then derived. Therefore the approach used is conservative, but it produces quite reasonable numbers. Because the missing points are weighted by small incoming radiation, the impact on the ASR is very small relative to the global mean, but it is desirable to do this step rather than treat the data as missing in order to provide fields that are continuous in space and time.

2) Global Imbalances: The reprocessing methodology we use takes into account recent estimates of uncertainty provided by the CERES Science Team (Wieliki et al. 2006) and the partitioning of the imbalance among longwave and shortwave fluxes.

Error Source
SW
LW
RT
Total Solar Irradiance
+1.0
0.0
+1.0
Absolute Calibration
1.0
1.0
2.0
Spectral Correction
0.5
0.3
0.8
Spatial Sampling
<0.1
<0.1
<0.1
Angle Sampling
+0.2
-0.1
+0.1
Time Sampling (diurnal)
<0.2
<0.2
<0.2
Reference Altitude (20 km)
0.1
0.2
0.3
Twilight SW Flux (-0.25 Wm-2)
<0.1
0.0
<0.1
Near Terminator SW Flux
+0.7
0.0
+0.7
3-D Cloud Optical Depth bias
+0.7
0.0
+0.7
CERES SRBAVG Ed2D RT
< 4.6
< 1.8
6.4

To address the inconsistencies between the retrieved TOA flux and recent estimates of the global imbalance based on ocean heat content tendency (e.g. Levitus et al. 2005) and land surface tendency (Huang 2006), we adjust the fields to be consistent with a 0.45 PW net warming of the climate system reported by Hansen et al. 2005. To do this, we adjust OLR upward uniformly by 1.5 W/m2. Albedo is then increased uniformly [by 4.338% of its original value for FM1 and 4.685% for FM2 - these correpond to adjustments of less than 0.5% in albedo terms] such that the global-annual-mean net flux at TOA is ~0.45 PW for the March 2000 to October 2005 period.


References:

  • Fasullo, J. T. and K. E. Trenberth, 2008: The annual cycle of the energy budget: Global mean and land-ocean exchanges, J. Clim, 21, 10, 2297-2313.
  • Fasullo, J. T. and K. E. Trenberth, 2008: The annual cycle of the energy budget: Meridional structures and poleward transports, J. Clim, 21, 10, 2314-2326.
  • Hansen, J., and co-authors, 2005: Earth's energy imbalance: Confirmation and implications. Science, 308, 1431-1435.
  • Huang, S., 2006: Land warming as part of Global Warming, EOS, 87, 31 Oct 2006, p44.Wielicki, B. A., K. Priestley, P. Minnis, N. Loeb, D. Kratz, T. Charlock,
  • D. Doelling, D. Young, 2006: CERES Radiation Budget Accuracy Overview, 12th Conf. Atmospheric Radiation, Madison , Wisconsin.