Normalized Insolation Clearness Index

[francoistardy]

Hello,
Could there be an error in your Normalized Insolation Clearness Index equation at this site:

https://power.larc.nasa.gov/docs/methodology/energy-fluxes/derived-parameters/

I use it with KT from your site, using your own solar azimuth angle, and consistently get values that are greater than 1.

Best regards,
François Tardy, Montreal

[ASDC - bmacpher]

Thank you for reporting this potential issue with the Normalized Insolation Clearness Index we are currently assessing the data.

Thank you,

Bradley

[ASDC - bmacpher]

Can you please provide a ___location of where you observe this issue in the POWER data?

Thank you,

Bradley

[ASDC - bmacpher]

We currently do not have the Normalized Insolation Clearness Index implemented in the POWER API but we plan to do so in the future. The equation you found on the POWER website was previously used. The previous equation used an approximation for airmass. In the future, when we reimplement the NKT equation we will be using Perez et al., 1990 (equation 1) that uses an updated expression for airmass.

Perez, R., Ineichen, P., Seals, R., and Zelenka A., 1990. Making full use of the clearness index for parameterizing hourly insolation conditions. Solar Energy, 45(2): 111-114.