In paleoclimate research, there always talking about the forcing factors, such as insolation and solar irradiance. However, I could not make it clear the difference between them. I have some knowledge about the latter one, which indicate the activity of the sun, such as sunspot, and could be measured by 10Be and 14C.
Could you shared some of your opinions on this? Thanks.
Dear Mingda, this is a good question. As I understand it, Insolation is measured in watt-hour per square metre (Wh/m2) and irradiance in watts per square meter (W/m2). Irradiance thus have more to do with the spectral or electromagnetic energy on a surface area at any instance of time, while Insolation is more the energy one can capture over a period of time.
kind regards, Gerro
Dear Dr.Prinsloo,
Thanks for your attention. You mentioned the unit between these two concepts are different. However, it seems the unit of them are both W/m2.
Here are the related papers,
Berger and Loutre 1991 on QSR (doi: 10.1016/0277-3791(91)90033-Q)
Steinhilber et al. 2009 on GRL (doi: 10.1029/2009GL040142, 2009)
Best wishes,
Dear All: The only difference is that the solar irrandence or activity is the measurement of sun radiation itself, for which Minda is right and nothing is relate to earth situation such as earth title, precession, etc, while isolation is the radiation to the top of atomospher of earth which is related to differnce hemisphers (north or south) and different latitudes related to earth obitor.
Yes, the irradiance essentially denotes the instantaneous rate in which power is delivered to a surface, while the insolation denotes the cumulative sum of the energy striking the surface for a specified time interval. There are many papers over years on these topics and I am sure you would have googled them already. I thought one simple write-up given by a solar cell company could demystify ( in a simpler way) the concepts. Pl see URL below:
http://sargosis.com/articles/science/intro-guide/irradiance-vs-insolation/
Irradiance is the rate of energy that is being delivered to a surface area at any given time. Its units are Watts per square meter. That means that for any given surface area A, there exists a specific amount of power P that is being delivered to that area in photonic form. The equation is shown below:
Irradiance = Power / Area
Insolation is the total amount of energy that has been collected on a surface area within a given time. While the irradiance denotes the instantaneous rate in which power is delivered to a surface, the insolation denotes the cumulative sum of all the energy striking the surface for a specified time interval. This interval must be specified in order to make sense, and the typical unit of time measurement is the hour. Since energy is equal to the rate of power P being delivered for a specified time T, the resultant insolation equation is as follows:
Insolation = Power * Time / Area
Insolation is a vague colloquial term, not a scientific quantity--at least not anymore
The terms to use are either irradiance (W/m2) or irradiation for accumulated energy over time (MJ/m2 or kWh.m2)
Chris is correct. Irradiance is the derivative and irradiation (insolation) is the integral. Insolation is not necessarily calculated top-of-atmosphere, but can also be calculated below plant canopies or incident upon structures. It is important to consider how they are measured. Solar radiation sensors generally have high sampling rates, so some averaging may be performed, while the angle of incidence can affect the responsivity of the detector.
https://www.campbellsci.com/solar-radiation
https://www.licor.com/env/products/light/
"a vague colloquial term, not a scientific quantity"???
Hmmm...
Solar radiation is the radiant energy emitted from the sun. Therefore:
Irradiance refers to the amount of solar radiation received per unit area by a given surface, expressed in kW/ m².
Insolation refers to the quantity of solar radiation energy received on a surface during an amount of time, expressed in kWh/ m².
Irradiance : W/m² (instantaneous and "power" concept)
Irradiation : Wh/ m² (accumulated and "work" concept)
Insolation may be one of the expressions of irradiation and abbreviation for "incident solar radiation".
So why does the IPCC use total irradiance in its models which only varies +/-1% rather than insolation which changes by up to 22%?
Is it because they need the sun's impact to not dwarf that of CO2
Insolation is a measurement of the cumulative energy measured over some area for a defined period of time (e.g., annual, monthly, daily, etc.). For these units to be interpreted correctly the time interval must be clearly stated (e.g., Wh, per square meter annual or Wh/ m²/year ).
Thanks, can you then perhaps explain why IPCC models rely on irradiance rather than insolation, when the latter clearly has a variable effect and the former does not
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