Dear Tony, Here is a paper Nikki Prive, I, and others submitted to Earth and Space Science that is relevant. Lidia also wrote a relevant paper and submitted it to Mon. Wea. Rev., but she should send it to you if she wishes. It's title is *The Value of Radio Occultation Data in Global NWP: An OSSE on the Impact of Profile Volume, Geographical Distribution, and Satellite Bias Correction.* My takeaway from both of these papers is that the number of observations is more important than their distribution for NWP. However, there are advantages to nearly uniform geographical and temporal coverage. With all satellites in the same polar orbits, there are gaps in local time coverage and this can be important in NWP for specific cases, such as tropical cyclone formation. Even though all local time coverage is of relatively minor importance to NWP, it is much more important for climate and essential for space weather. All considered, a mix of low- and high- inclination constellations is optimal for all purposes, and our 20K profiles per day number is still a good goal. I am sorry I won't be at the IROWG meeting in September. Rick Dr.Richard A. Anthes President Emeritus University Corporation for Atmospheric Research 3090 Center Green Drive Boulder, CO 80301 Office: FL-4 Room 3248 Phone: 303-497-2617 Fax: 303-497-2610 On Thu, Jul 16, 2026 at 1:15 PM Mannucci, Anthony J (US 3620) via Announcements <announcements@lists.irowg.org> wrote:

Dear IROWG colleagues, At the latest Coordination Group for Meteorological Satellites (CGMS) plenary meeting (June 2026), IROWG was notified that CGMS Working Group III (WGIII) tasked IROWG with coordinating a scientific assessment of the impact of the decline in COSMIC-2 radio occultation (RO) observations expected as the constellation ages. The IROWG assessment is to inform the next WGIII Risk Assessment Workshop (24–26 February 2027). FYI, IROWG is under CGMS-WGII (Satellite data and products), while WGIII is the Working Group on Operational Continuity and Contingency Planning. The action reads:

*Action #*

*Actionee*

*AGN item*

*Description*

*Action feedback/closing document*

*Deadline*

*Status*

*54.01p_wgiii*

IROWG

WGIII

IROWG to assess the impact of the decline in COSMIC data availability, possibly distinguishing between the respective contributions of low- and medium-inclination orbit, and analysing the number of RO required to mitigate the risk

4 June 2026 - A follow-up call will be arranged to better understand how the action item supports agency priorities - IROWG can help coordinate an assessment - The timeline for completing the assessment depends on the detailed plan for conducting the assessment

End of 2026

(9th WGIII RAWS: 24-26 Feb 2027)

*OPEN*

WGIII has indicated that “we do not need IROWG to weigh in on the potential acquisitions strategies for data, but rather to provide information about what data is needed to maintain capabilities and/or mitigate loss of COSMIC-2.The purpose of the action is for IROWG to provide information to WGIII in advance of the next Risk Assessment to inform WGIII discussion/evaluation of risk posed by degradation/loss of COSMIC-2 and, if needed, discussion of potential contingencies to mitigate loss of COSMIC-2. The questions WGIII would like the IROWG to answer are:

1. >From a scientific perspective, what is the minimum number of equatorial (low inclination) RO needed to maintain current performance of operational NWP 2. Define what they mean by low inclination (clarify the orbital characteristics for low inclination so we can be sure we are all talking about the same thing) 3. Identify if there are options to use increases in the number of non-low inclination RO to mitigate the loss of COSMIC 2 and if so, to be specific about how many additional occultations (be specific about number and distribution needed). "

The IROWG Co-Chairs will meet with WGIII shortly after IROWG-11 (September 2026) to provide an update on the community's progress. Therefore, we would like to begin gathering relevant information before the workshop and continue the discussion during IROWG-11.

We would greatly appreciate hearing from anyone who has:

- existing publications, reports, or presentations relevant to the impact of declining COSMIC-2 observations; - ongoing studies or planned work related to this topic; - operational or research experience that could help inform the scientific assessment.

We recognize that IROWG is an international scientific working group, and contributions are entirely voluntary. Existing analyses, ongoing work, and expert perspectives are all valuable.

If there is sufficient interest, the IROWG Co-Chairs would also be happy to organize an informal community discussion before IROWG-11 to exchange ideas and help facilitate discussion during the workshop.

If you have relevant material or would like to contribute to this assessment, please contact the IROWG Co-Chairs at your convenience.

Thank you in advance for your help and for supporting this community effort.

Best regards, Hui Shao and Uli Foelsche, IROWG Co-Chairs Tony Mannucci, IROWG Rapporteur

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