Organization(s):

National Oceanic and Atmospheric Administration (NOAA), Earth System Research Laboratory (ESRL)

What does this program measure?

Total Downwelling solar and thermal infrared radiation (or irradiance) is measured in units of Watts per square meter. Aaerosol optical depth is also measured.

*** The Mauna Loa Observatory record of solar transmission of sunlight is the longest continuous record of this nature in existence.

How does this program work?

We primarily use commercial thermopile broadband radiometers to measure the irradiance and aerosol optical depth, a measure of the total dust and particle load of the atmosphere, is measured with a sunphotometer.

Measurement	Instruments	Frequency	Site
Global Irradiance	Eppley Pyranometers with Q, OG1, and RG8 filters	continuous	MLO
Direct Irradiance	Eppley pyrheliometer with Q filter(2)	continuous	MLO
Direct Irradiance	Eppley pyrheliometer with Q, OG1, RG2, and RG8 filters	3/day (weekdays)	MLO
Direct Irradiance	Eppley/Kendall active cavity radiometer	continuous	MLO
Diffuse Irradiance	Eppley pyrgeometer with shading disk and Q filter (2)	continuous	MLO
UV Solar Radiation	Yankee Environmental UVB pyranometer (230-320 nm)	continuous	MLO
Diffuse (IR) Irradiance	Terrestrial downwelling IR pyrgeometer with shading disk	continuous	MLO
Column Water Vapor	2 two-wavelength tracking sunphotometers: 860, 940 nm	continuous	MLO

Why is this research important?

Solar and infrared radiation are fundamental ingredients in maintaining the current climate, and also play a major role in anticipated changes in that climate. Aerosol optical depth helps quantify the role of aerosol in radiatively forced climate change.

Are there any trends in the data?

Read a MLO Solar Irradiance publication (.pdf format)

While no persistent long-term trends have been detected, there are excursions of several years in duration following major volcanic eruptions and there appears to be increased springtime aerosol loading in the last few years.

As the plot below shows, aerosols from large volcanic eruptions block some sunlight from reaching the earth's surface. Note how the lidar measurements of the volcanic aerosols in the stratosphere anti-correlate with the solar record.

How does this program fit into the big picture?

What is it's role in global climate change?

Solar and thermal infrared (IR) radiation are vehicles for climate change but at the same time are affected by that change. Our radiation measurements can be used to investigate both the causes of and the response to climate change.

Comments and References

• Dutton, E. G., J. J. DeLuisi, and A. P. Austring, 1985. Interpretation of Mauna Loa
• Atmospheric Transmission Relative to Aerosols, Using Photometric Precipitable Water Amounts. J. Atmos. Chem., 3, 53-68.
• Dutton, E.G., 1992. A Coherence Between the QBO and the Amplitude of the Mauna Loa Atmospheric Transmission Annual Cycle. International J. Climatology 12, 383-396.
• Dutton, E.G. and J.R. Christy, 1992. Solar Radiative Forcing at Selected Locations and Evidence for Global Lower Tropospheric Cooling Following the Eruptions of El Chichón and Pinatubo. Geophys. Res. Lett. 19, 2313-2316.
• Dutton, E.G., P. Reddy, S. Ryan, and J.J. DeLuisi, 1994. Features and effects of optical depth observed at Mauna Loa, Hawaii: 1982-1992. J. Geophys. Res. 99, 8295-8306.
• Dutton, E.G. and B.A. Bodhaine, 2001: Solar irradiance anomalies caused by clear-sky transmission variations above Mauna Loa 1957-1999. J. Clim., 14, 3255-3262.