The first instance of the changeover was with the Cooperative Hurricane Upper Air Stations (CHUAS) Radiosonde Observations System (CROS) during the winter of 2015-2016. Since the changeover, the sites have become more reliable as there are fewer parts with the potential for failure, and an upgrade in the functionality of the software being utilized. In addition to the frequency changeover, the CHUAS network switched over from radiosondes with Radio Direction Finding (RDF) generated winds to radiosondes with Global Positon System (GPS) generated winds. Within the past year, the NWS has been required to transition additional upper air stations to 403 MHz systems due to the launching of the GOES-R satellite. Multiple upper air stations are located in close proximity to the GOES-R downlink stations, and it was determined the current operational radiosondes could pose some interference to the satellite downlink. This prompted the NWS to develop the Transitional Radiosonde Observing System (TROS) which will be deployed during the fall of 2016 at eight sites within the NWS upper air network.
This paper will discuss the operational observations conducted at the sites which have been transitioned to the 403 MHz center frequency and the processes which occurred in order for this transition to ensue. It will also confer the additional updates to the NWS Upper Air network to 403 MHz in the future.