1-01-01 Addition of variable definitions (part 2: lightning)

[fstuerzl]

Proposal Summary

Please consult the Guidance and use the following structure for new issues. Note, the content in this initial comment box is subject to modification to document the final decisions or to provide more details as needed.

Summary and Purpose

Add definitions to lightning variables.

Proposal

(definitions updated) notation	path	name	description
new	\Atmosphere\Lightning\Total lightning (flash) density	Total lightning (flash) density	Total number of detected flashes in the corresponding time interval and space unit. Note: The space unit (grid box) should be equal to the horizontal resolution and the accumulation time to the observing cycle
new	\Atmosphere\Lightning\Lightning (flash) density cloud-to-ground	Lightning (flash) density cloud-to-ground	Number of detected cloud-to-ground flashes in the corresponding time interval and space unit. Note:
258	\Atmosphere\Lightning\Lightning discharge polarity	Lightning discharge polarity	Polarity of the charge effectively lowered to ground during a lightning discharge.
259	\Atmosphere\Lightning\Lightning discharge rates	Lightning discharge rates	Number of lightning discharges per unit time in a given region (e.g. world-wide) or for a given storm system (e.g. a thunderstorm cell).
260	\Atmosphere\Lightning\Lightning discharge type (cloud to cloud, cloud to surface)	Lightning discharge type (cloud to cloud, cloud to surface)	Lightning discharge type, defined by the path of the lightning discharge: between two clouds or the same cloud (intra-cloud) or between cloud and ground (cloud-to-ground).
432	\Atmosphere\Lightning\Position\Lightning direction from station	Lightning direction from station	Azimuth of the lightning event with respect to the corresponding station.
433	\Atmosphere\Lightning\Position\Lightning distance from station	Lightning distance from station	Distance of the lightning event from the corresponding station.

new

(supersedes current 257) notation	path	name	description
tbd	\Atmosphere\Lightning\Lightning discharge current	Lightning discharge current	Current incurred by the lightning discharge.

deprecate

notation	path	name	description
257	\Atmosphere\Lightning\Lightning discharge energy	Lightning discharge energy

Reason

Every entry in the WMDR code lists should have a useful definition.

Stakeholder(s)

[include names and emails or handles of individuals or groups that introduced the proposal]

Consultations

@sibalm (Simone Balmelli, MeteoSwiss)

@hpohjolawmo (Heikki, WMO)

@gaochen-larc (Will Mc Carty)

@tjlang (Timothy Lang)

@deeplycloudy (Eric Bruning)

@... (Steve Goodman)

@... (Pekka Rossi)

Context

[include references to manuals or guides that are reviewed to ensure alignment, if proposal differs then document how and why]

Expected Impact of Change

LOW

[fstuerzl]

Variables 12001 and 12002 are included in OSCAR/Requirements, so I suggest to use the definitions provided there:

Name	Definition
Total lightning density	Total number of detected flashes in the corresponding time interval and the space unit. The space unit (grid box) should be equal to the horizontal resolution and the accumulation time to the observing cycle
Cloud to Ground lightning density	Number of detected cloud-to-ground flashes in the corresponding time interval and the space unit. The space unit (grid box) should be equal to the horizontal resolution and the accumulation time to the observing cycle

[amilan17]

subset of issue #190

[joergklausen]

I have reached out to a colleague on this one.

https://library.wmo.int/?lvl=notice_display&id=220 may also contain some useful descriptions.

[JohnEyre]

OSCAR/Requirements currently contains two lightning variables:

• total lightning density,
• cloud to ground lightning density. So there is a clear match here, and the only issue is the ordering of the words in the variable name.

[sibalm]

This is a proposal for the descriptions notation | path | name |  description -- | -- | -- | -- 12001 | \Atmosphere\Lightning\Total lightning density | Total lightning density | Total number of detected flashes in the corresponding time interval and space unit. 12002 | \Atmosphere\Lightning\Lightning density cloud-to-ground | Lightning density cloud-to-ground |  Number of detected cloud-to-ground flashes in the corresponding time interval and space unit. 257 | \Atmosphere\Lightning\Lightning discharge energy | Lightning discharge energy | Energy released by the lightning discharge. 258 | \Atmosphere\Lightning\Lightning discharge polarity | Lightning discharge polarity | Polarity of the charge effectively lowered to ground during a lightning discharge.  259 | \Atmosphere\Lightning\Lightning discharge rate | Lightning discharge rate |  Number of lightning discharges per unit time in a given region (e.g. world-wide) or for a given storm system (e.g. a thunderstorm cell) 260 | \Atmosphere\Lightning\Lightning discharge type (intra-cloud, cloud-to-ground) | Lightning discharge type (intra-cloud, cloud-to-ground) | Lightning discharge type, defined by the path of the lightning discharge: between two clouds or the same cloud (intra-cloud) or between cloud and ground (cloud-to-ground). 432 | \Atmosphere\Lightning\Position\Lightning direction from station | Lightning direction from station | Azimuth of the lightning event with respect to the corresponding station   433 | \Atmosphere\Lightning\Position\Lightning distance from station | Lightning distance from station | Distance of the lightning event from the corresponding station

[sibalm]

And here are some further comments:

12001-12002) Optionally, we may replace the name "Total lightning density" by "Total lightning flash density", and "Lightning density cloud-to-ground" by "Cloud-to-ground lightning flash density", to make it clear we are speaking of flashes. The sentence: "The space unit (grid box) should be equal to the horizontal resolution and the accumulation time to the observing cycle" may not be appropriate for lightning data. Indeed, lightning data do not have a uniquely defined horizontal resolution (the localization accuracy varies for each event) nor observing cycle (lightning events are detected in real time). So, there is no unique space and time unit for defining the lighting density. A typical definition of lightning density is #events/km^2/min A last comment: we may also consider adding "lighing discharge" densities; in this case, we don't speak of flashes anymore, but of their subcomponents (strokes and pulses). These correspond e.g. to the lightning events that are plotted in NinJo.

257-) Lightning energy is difficult to measure, and is not, for instance, part of the data we receive from Météorage. Instead, we receive the measurement of the lightning current intensity (measured in kA). It may be meaningful to add the current intensity as a new voice of the lightning vocabulary, or even to replace the lightning energy by it.

259-) As you see by the description, the concept of "lighting discharge rate" is not unique, as it can be applied to different contexts (regions, thunderstorm cells,...). Does it makes sense to keep this voice? Or shall we specify it better?

432-433) We may replace "lightning" by "lightning discharge", so that it is clear we are not speaking of lightning flashes. Notice: we receive lightning data on the whole COSMO-Alps domain. The stations mentioned here (I presume, in our case, Swissmetnet stations), are not responsible for the lightning detection (instead, a network of Météorage antennas makes the detection). For historical and climatological reasons, we however classify lightning data depending on the distance from each SwissMetNet station. I cannot judge whether it makes sense to keep these voices here, but it must be clear that these parameters are somehow "artificial".

Best regards,

Simone Balmelli

[JohnEyre]

@sibalm @joergklausen @amilan17 . Thanks for these explanations. I suggest that we also check with experts on lightning imagery from satellites, as I know that the processing of these data (and hence potentially the data dissemination) uses many of these concepts. WMO Space Programme will have the appropriate contacts.

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/Meeting-2022.09.22 notes:

• @joergklausen will work on this
• @amilan17  ask Heikki to help find someone from the space-based lightning community to review
• @gaochen-larc can reach out to Will McCarty

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2022.10.06-TT-WIGOSMD meeting notes:

no progress yet

[amilan17]

Steve Goodman from NOAA can provide some feedback after October

[joergklausen]

Definitions provided by @sibalm make sense. Still need to agree on remaining comments, paraphrased here:

• 12001: Optionally, replace the name "Total lightning density" by "Total lightning flash density"
• 12002: Optionally, replace "Lightning density cloud-to-ground" by "Cloud-to-ground lightning flash density", to make it clear we are speaking of flashes.
• (new) Also consider adding "lightning discharge" densities; in this case, we don't speak of flashes anymore, but of their subcomponents (strokes and pulses).
• 257: Supersede "Lightning energy" by (new) "Lightning current intensity" (measured in kA).
• 259: The concept of "lighting discharge rate" is not unambiguous, as it can be applied to different contexts (regions, thunderstorm cells,...). Does it makes sense to keep it? Or is there a need for better specification?
• 432: Suggestion to replace "lightning" by "lightning discharge", so that it is clear we are not speaking of lightning flashes.
• 433: Suggestion to replace "lightning" by "lightning discharge", so that it is clear we are not speaking of lightning flashes.

Need comments from @hpohjolawmo and @gaochen-larc (Will Mc Carty) and @joergklausen (Urs Germann)

[joergklausen]

I reached out to Urs Germann, but he doesn't feel compenent enough to provide additional insight.

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2022.11.03-TT-WISOSMD notes: @amilan17: Heikki will provide some feedback soon

[amilan17]

@sibalm thank you for your contributions to the definitions of these proposals. Can you please update your profile with your full name and affiliation? I like to document who has contributed to proposals for amendments when submitting for approval. Thanks. Anna (WMO Secretariat)

[joergklausen]

Proposal updated. Need review by @hpohjolawmo (Heikki) and @gaochen-larc (Will McCarthy)

[amilan17]

@joergklausen I don't see any changes in the proposal summary. Am I missing something?

[joergklausen]

@joergklausen I don't see any changes in the proposal summary. Am I missing something?

I had to redo this, left the page before updating, apparently ...

[amilan17]

Review from Heikki, Steve Goodman and Pekka Rossi

**

• According to GitHub thread is not clear what was the reason for the proposed change of 12001 and 12002 from “total lightning density” to “total lightning flash density”. This is causing an issue for the existing measurement when total lightning density is not always based only on flash measurements. Thus, we think it is better to keep it as it is, or then create additional codes for all total densities based on all variables.
• Also, existing codes are based on the ground based lightning detection systems and they are not supporting space-based measurements. Additional codes should be created to support space-based lightning detection. It should take into account pulses, events, groups and flashes. It should also cover the optical energy measured by space based lightning detection system. However, The fundamental idea that WMDR codes are technology independent should be kept in mind.
•  We propose additional review to be done for entire code library related to lighting detection before any changes, and then to create the next version of the codes supporting all existing lighting detection technologies.

**

and 

**

If your objective is to system agnostic then perhaps fewer codes is better, for example,

• Ground based RF space-based optical
• Stroke…..…………………… group 
• Pulse ………………………… event
• Flash …………………………. Flash
• Peak current (kA)………………. Radiance (fJ) 
• Polarity………………………… N/A 

**

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2022.11.22-TT-WIGOSMD notes:

@joergklausen will reach out to collaborators to see if they are willing to form a temporary editing team to finalize this proposal such that it represents sattelite and ground observations.

[sibalm]

@sibalm thank you for your contributions to the definitions of these proposals. Can you please update your profile with your full name and affiliation? I like to document who has contributed to proposals for amendments when submitting for approval. Thanks. Anna (WMO Secretariat)

@amilan17 I have updated my profile. Please tell me if you need more information. Thank you!

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2023.02.16-TT-WIGOSMD notes:

Anna will follow up with organizing a side meeting with specific experts.

[deeplycloudy]

I was invited to join this conversation Gao Chen as a result of a side conversation with @tjlang, who I will take the liberty of quoting:

I think lightning flash extent density (FED) may be a useful addition to the WMO metadata standards. FED, which is calculable from anything that measures the horizontal extent of lightning flashes (including LIS, GLM, MTG-LI, and Lightning Mapping Arrays), is very helpful for understanding where lightning occurs.

I agree with this idea. It would be useful to distinguish between quantities that arise from lighting mapping (which accounts for the spatial extent of lighting discharges) and point-location measurements.

For point-location and mapped flashes, the respective terms in my mind would be “flash density" and "flash extent density,” as suggested by Timothy.

We could also add “flash area,” which now has use in US NWS operations, and is another basic measurement made by lightning mapping systems.

[tjlang]

Note that flash density has units of inverse area inverse time (e.g., number of flashes s^-1 km^-2). Flash extent density (FED) is similar except here you count number of flash portions that pass thru a given area in a given time. So even if the flash centroids are elsewhere you can have portions of them pass thru a given area in a given time as the lightning channels propagate. Flash area is just basic area units (e.g., km^2).

[joergklausen]

@amilan17 Please set up meeting with all stakeholders mentioned in issue. Suggestion: 28 March or 30 March. Thanks

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2023-03-17-TT-WIGOSMD notes: @amilan17 set up meeting with stakeholders

[joergklausen]

IMHO, the only way forward here is to organize this meeting suggested earlier.

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2023.06.01-TT-WIGOSMD notes:

• no progress
• @amilan17 will try to set up a meeting soon

[joergklausen]

@amilan17 Setup a MS Teams meeting with Tim Lang, John Eyre, Simone Balmelli, Heikki

[meulenvd]

@joergklausen has asked me to give this action new momentum because it seems almost solved but not really finalized. Taking notice of all the comments, I have concluded that in fact the discussion is much broader and I can split this issue into the following activities:

1. modification of the existing notations 12001, 12002, 258, 259, 260, 432 and 433 and replacement of 257 by a new notation
2. introduction of new, alternative notations
3. introduction of new notations in line with satellite based products because the present notations are largely associated with surface based observations
4. additional review to be done for the entire code library related to lighting detection to generate a more complete or better structured set; may be a complete reorganization of all lightning associated notifications.

So, in order to speed up, it may be better to finalized first activity no. 1 and than follow up with the others.

w/r 1: For the current proposal (see on top), I think acceptance is straightforward at present. One suggestion is still open (see comment by @joergklausen: 432 (direction) and 433 (distance): Suggestion to replace "lightning" by "lightning discharge", so that it is clear we are not speaking of lightning flashes.

w/r 2: mentioned in the comment by @deeplycloudy and @tjlang a new notation is suggested: lightning flash extent density (FED). However the notations with lightning (flash) density are comparable and distinction between a new notation and the existing ones must be clear to avoid confusion.

w/r 3: This would be a separate activity, dedicated to experts working on lightning observations by satellites. I recommend to take note of the new (2021) Volume IV of the GIMO (WMO-No. 8) on Space-based Observations and with paragraphs describing the technology to determine and observe lightning from space. For an excerpt from this Volume on lightning, see: 8_IV_2021_en(Excerpt on Lightning).pdf

w/r 4: A overall review of the entire code library is proposed. It will help to improve consistency, although such a review may result in a major revision of the present naming convention (flash, discharge, etc.). Although the WMDR codes should be technology free, most notations are linked to available observation techniques. So, this review will be quite a challenge and time consuming. For this activity I recommend to take note of the new version of the chapter on Lightning Detection in GIMO, Volume III (WMO-No. 8). The latest version is approved by EC-76 mid 2023, see: 8_III_6_en_LCP.pdf

So, I kindly request all contributors to give there comments on this proposal, in particular @sibalm (Simone Balmelli, MeteoSwiss), @hpohjolawmo (Heikki, WMO), @gaochen-larc (Will Mc Carty), @tjlang (Timothy Lang), and @deeplycloudy (Eric Bruning).

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2024.02.15-TT-WIGOSMD notes: Jitze added a proposal in GH (see above) with no comment yet; will follow through with an email;

[JREyre]

@meulenvd @joergklausen @amilan17 This Issue is still in need of expert review, and I hope that contacts established by Jitze will achieve this. At the end of the day, we need a set of names and definitions that are acceptable to both space-based and surface-based observing communities, because they are both trying to provide observational information on the same geophysical phenomena. However, it would be acceptable for some variables to relate only to space-based or only to surface-based observations (and, in these cases, the definitions should make this clear).

[meulenvd]

@joergklausen @amilan17 @JREyre Separate E-mail send to @sibalm @hpohjolawmo @gaochen-larc @tjlang @deeplycloudy, requesting comments, see e-mail (2024-02-19) issue 391.pdf

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2024.04.09%E2%80%90TT%E2%80%90WIGOSMD notes: @amilan17 to organize a meeting with relevant parties; John recommends just having a meeting with key experts;

[amilan17]

@meulenvd and I agree to move forward with step 1 (see attached). If/when we need other codes, new amendments can be proposed at that time. The original purpose here was to add missing definitions.

lightning-issue391.docx

[meulenvd]

see list of steps w/r step 2 and 3 (introduction of new or alternative notations in line with satellite based products) the following information on

• Flash extent density (FED)
• Average flash area (AFA) and
• total optical energy (TOE)

might be of interest:

• GOES-R Lightning Detection Fact Sheet
• A Global LIS/OTD Climatology of Lightning Flash Extent Density

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/2024.05.16%E2%80%90TT%E2%80%90WIGOSMD notes: team agrees to move forward with proposal as is.

[amilan17]

@joergklausen branch is updated