The proposed work will assess long-term ozone trends from data collected by NOAA and its predecessors since the 1960s. The 1990 amendments to the US Clean Air Act responded to the US signing of the 1987 Montreal Protocol requires NOAA and NASA to monitor ozone and the reduction of ozone depleting substances. Signs of ozone recovery are occurring in the upper stratosphere. Questions are: is the ozone layer recovering globally and at what levels; and is the recovery at the rate expected from the reduction of ozone-depleting substances? To support this requirement NOAA�??s Earth System Research Laboratory, Global Monitoring Division (ESRL/GMD) ozone monitoring program performs ground-based (GB) observations of total column ozone with the stable, well-calibrated Dobson Spectrometers. Changes in vertical ozone profiles are assessed with the Dobson Umkehr technique at 5 stations. These measurements are supplemented by balloon-borne ozonesonde instruments from 10 stations in collaboration with the NASA Southern Hemisphere ADditional OZonesondes (SHADOZ) program. Additionally NASA and NOAA provide satellite measurements of ozone profiles through the Solar Backscatter Ultraviolet (SBUV) and related instruments on NASA�??s Nimbus-4 and -7, and on the NOAA Polar Orbiting Environmental Satellites (NPOES) yielding 40 years of continuous data. Since 2014 the Ozone Mapper Profiler Suite (OMPS) on Suomi National Polarorbiting Partnership (S-NPP) and recently the Joint Polar Satellite System (JPSS) augment the SBUV series. The SBUV Coherent dataset (SBUV COH) homogenizes data from these instruments to create a trend quality zonal mean dataset. This proposed project will integrate SBUV/OMPS satellite and NOAA�??s GB data to ascertain how limited geospatial sampling can impact the accuracy of trends derived from the GB records. We will select satellite ozone observations over the GB stations, both by closest geographical proximity and by dynamical matching using equivalent latitude. To interpret trends and stratospheric ozone variability we will use dynamical and chemical tracers from the NASA Global Model Initiative (GMI) chemistry transport model (CTM). The model uses interactive chemistry and transport, driven by re-analyses data (MERRA2) to simulate hourly ozone fields since 1979. GMI simulations and SBUV overpass records will be used to study the effects of limited sampling in ground-based observational records that may be an issue for trend analyses. The stated goal of this funding opportunity is �??explain various trends, patterns and extremes detectable in the existing long-term observational records�?�, in support of NOAA�??s long-term research goal to �??provide essential environmental information vital to our Nation�??s safety, prosperity and resilience�?�. This study supports both, by deriving trends from the GB stations and satellite records, while investigating causes for the differences related to sampling limitations, to the representativeness of equivalent latitudes and to stability of the records. The outcome of this study will provide ozone recovery rates over the globe, will provide recommendations for improving network coverage and modeling products that can be used directly by policy makers and other stakeholders, and will improve attribution of ozone regional variability to the global circulation processes through the use of the explanatory parameters derived from the NASA CTM simulations of ozone profiles at the location of ground-based stations.