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Context: Solar sectoral Rossby waves have only recently been unambiguouslyidentified in Helioseimsic and Magnetic Imager (HMI) and Michelson DopplerImager (MDI) maps of flows near the solar surface. So far this has not beendone with the Global Oscillation Network Group (GONG) ground-basedobservations, which have different noise properties.  Aims: We utilize 17 years of GONG++ data, to identify and characterize solarRossby waves using ring-diagram helioseismology. We compare directly with HMIring-diagram analysis.  Methods: Maps of the radial vorticity are obtained for flows within the top 2Mm of the surface for 17 years of GONG++. The data is corrected for systematiceffects including the annual periodicity related to the $B_0$ angle. We thencompute the Fourier components of the radial vorticity of the flows in theco-rotating frame. We perform the same analysis on the HMI data that overlap intime.  Results: We find that the solar Rossby waves have measurable amplitudes inthe GONG++ sectoral power spectra for azimuthal orders between $m=3$ and$m=15$. The measured mode characteristics (frequencies, lifetimes andamplitudes) from GONG++ are consistent with the HMI measurements in the overlapperiod from 2010 to 2018 for $m\le9$. For higher-$m$ modes the amplitudes andfrequencies agree within two sigmas. The signal-to-noise ratio of modes inGONG++ power spectra is comparable to HMI for $8\le m\le11$, but is lower by afactor of two for other modes.  Conclusions: The GONG++ data provide a long and uniform data set to studysolar global-scale Rossby waves from 2001.

Solar Rossby waves observed in GONG++ ring-diagram flow maps