I attended the 4th Annual SORCE Meeting: âEarthâs Radiative Budgetâ?, and was impressed by the research being conducted on the role of solar forcing on the Earthâs climate. This group of scientists are clearly represent the world leaders in assessing solar forcing of the Earthâs climate system. Last week I presented extracts from several of the talks, and here I will present excerpts of my notes for the meeting.
The total solar irradiance in near real time can be obtained from several websites (see). An interesting finding at the meeting is that the âsolar constantâ? value used, based on a multi-year time average is slightly smaller than is typically used and is 1361 Watts per meter squared. This value does vary over time in several interesting ways (see and see). For example, In October 2003 there was a sharp drop in total solar irradiance due to the passage of several large sunspots across the face of the Sun. When the surface of the Sun is dominated by plages, an increase in total solar irradiance occurs. Over the period since early 2004, there has been a small decrease up to the present.
The solar spectrum also varies in time (see). Several presentations discussed the significance of the observed variations in the solar spectrum. Jerry Harder stated, for example, that the
âgreatest absolute variability occurs in mid visible (direct)â? solar radiation and that the ârelative uncertainty in solar forcing is very large and must be reduced in order to separate natural and anthropogenic forcingâ?.
In terms of how the climate system responds to solar forcing, Robert Cahalan concluded in this talk that using âcloud fraction for radiation [effects] is an inadequate âband aidââ? and that ânone of the 1-D schemes work.â?
His abstract also presents this conclusion where he wrote, â The interaction of clouds with solar and terrestrial radiation is one of the most important topics of climate research. Because of the complexity of clouds, only full three-dimensional (3D) treatment of this interaction can provide answers to many climate and remote sensing problemsâ¦â?
Another valuable source of solar forcing data is the Geostationary Radiation Budget Experiment (GERB), which was discussed by Steven Dewitte. This is new data (and became available for public use in March; see) will further expand our understanding of solar forcing. The animations from these satellite data are very informative (see), and show the complex regional variations in solar forcing and in the total radiation budget.
Roger Davies presented time series of deseasonalized 10-day and annual anomalies related to the TOA radiation budget analyzed from MISR measurements, from early 2000 to the present. He concludes, as stated in his abstract that,
“The biggest interannual global anomalies observed by MISR that affect the top of atmosphere radiative budget appear to be those in the effective cloud height. These show interesting decreases through 2005, averaging about 10m/yr. On a regional basis, the largest signal occurs systematically in the InterTropical Convergence Zone, associated with a reduction in high cloud fraction. The 2006 data appear, however, to be showing an increase in height.”
MISR is the âMultiangle Imaging SpectroRadiometerâ? which images Earthâs climate system simultaneously at 9 different angles;). His analysis of the MISR satellite data further illustrates the significant temporal and regional variability in climate data which is not accurately simulated (or understood) using climate models.
Judith Leanâs presentation entitled âSolar Radiative Forcingâ? updated our understanding of the magnitude of total solar irradiance. In her abstract, she stated,
âSimulations of the evolution of magnetic flux on the Sunâs surface suggest a secular total irradiance increase of order 0.08% during the past three centuries, which is less then the increase of 0.2-0.4% inferred from earlier studies of variations of Sun-like stars and cosmogenic isotopes.â?
The discussion of the SORCE talks will continue this week.