ASDC - cheyenne.e.land wrote:
> Hello we apologize for the delay, but thank you for using POWER,
>
> The Services Version 2 of POWER provides Data Version 901 POWER data
> (Services Version 1 provided Data Version 801). The Data Version 901
> improves the 1) underling source data models and 2) enhances traceability
> to source data models. Specifically, the underling source data models for
> radiation-based parameters has changed from SRB v3 to SRB v4 for 1984
> through 2000. From 2001, we now provide CERES SYN1deg until three months
> before present time. Like in previous versions, POWER continues to provide
> support for Near Real Time (NRT) availably with FLASHFlux. For the enhanced
> traceability, Data Version 901 POWER data includes improved parameter
> abbreviations and definitions, in order to be more clear about what
> parameter is being used. The most prominent change is that POWER provides
> data at the underlying source data model's grid resolution.
>
> So, changes in the values are to be expected:
>
> [list]For meteorology-based parameters, we are no-longer using bilinear
> interpolation to put the source data on a common 0.5 x 0.5 degree grid as
> it was in Data Version 801 (to enhance traceability). Not using
> interpolation causes some slight variation in the values compared to the
> previous version, but the values are exactly the same as the source dataset
> for a particular point location. The differences in values between Data
> Version 801 and 901 could be more pronounced for a specific point location
> if:
>
> [list=2]the location is close to a land/sea boundary.[/list]
> [list]the location is close to the grid box boundary (since the data could
> potentially have pulled from a adjacent grid box when it was not using
> original source data grid). [/list][/list]
>
> [list]For solar-based parameters, we are no-longer replicating the source
> data on a common 0.5 x 0.5 degree grid; we changed the underling source
> data models to newer versions. For more information, please review the data
> sources
> [url=
https://power.larc.nasa.gov/docs/methodology/data/sources/]here[/url].[/list]
> [list]The elevation, or altitude, is also not interpolated so the same
> reasons for meteorology-based parameters apply.
> [/list]
>
> For this parameter in specific, Equivalent no sun days is calculated using
> the formula:
>
> [img]
https://i.postimg.cc/jCYrxx5R/Screen-Shot-2022-08-10-at-3-51-55-PM.png[/img]
>
> Converting Minimum Available Insolation Over a Consecutive n-day period to
> Minimum Available Insolation Over a Consecutive n-day period (%) uses the
> following formula:
>
> [img]
https://i.postimg.cc/sxYhmJMy/Screen-Shot-2022-08-10-at-4-06-36-PM.png[/img]
>
> The difference you are experiencing is due to the revised parameter
> definitions and the formula that we have used. The parameter
> “EQUIV_NO_SUN_BLACKDAYS_MONTH” (2019), “NO_SUN_BLACKDAYS_MAX” (2021), and
> “MAX_EQUIV_NO_SUN_DAYS” (now) refer to the same parameter. The most recent
> values are the correct ones.
>
> Regards,
> ASDC User Services
I really appreciate the detailed follow up. Was this always the formula used and if not is there any way of getting the older parameters back?
For reference I had the older definitions commented in my code -
EQUIV_NO_SUN_BLACKDAYS_MONTH” (2019) - Equivalent number of NO-SUN or BLACK days is the number of days that a backup storage system must provide energy to account for the expected days without solar insolation.
NO_SUN_BLACKDAYS_MAX” (2021) - The maximum number of consecutive days that a backup storage system must provide energy to account for the expected days without solar insolation
MAX_EQUIV_NO_SUN_DAYS” (now) - Maximum equivalent no sun days is the maximum or the worse no sun days among all consecutive n-day equivalent no-sun days in a particular month
Based on the older definitions, I was led to believe you were tracking consecutive no-sun days in a given month (which is useful for spec'ing battery bank sizes) whereas now it's a total number of no-sun days over a consecutive period (which would tell the total number of days in a month that the battery bank would run in a deficit but not necessarily consecutively?).
Again, thank you for your help