NASAs High-Resolution GEOS Forecasting and Reanalysis Products: Stratospheric Intrusions at GMAO

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A Study of the Meteorological Conditions Associated with Anomalously Early and Late Openings of a Northwest Territories Winter Road

In the Canadian Arctic, winter roads are engineered across the frozen land, rivers, and lakes. The strength and longevity of these roads depend on particular weather conditions. Our research focuses on the winter road between Tulita and Norman Wells, Northwest Territories, which has been maintained officially by the territorial government since 1982. Statistical analysis of the opening dates for the winter road showed five seasons with extremely early dates and five with extremely late dates. The extremely early-opening seasons are distinguished by anomalously high sea-level pressures, anomalously cold tropospheric air, and northwesterly surface winds during the November prior to the road opening. The extremely late-opening seasons are characterized by an anomalously strong Aleutian low in the preceding November. The extremely late-opening years are correlated with strong El Niño seasons, whereas the extremely early-opening years are not systematically associated with teleconnection patterns. Our analysis of meteorological conditions near Norman Wells, associated with the extreme opening dates for this winter road, may provide planners with more precise information germane to this road construction.Dans l’Arctique canadien, les routes hivernales sont construites sur le sol, les lacs et les rivières gelées. La solidité et la durabilité de ces routes dépendent de conditions météorologiques particulières. Nos recherches mettent l’emphase sur la route hivernale officiellement entretenue par le gouvernement territorial depuis 1982, entre Tulita et Norman Wells dans les Territoires du Nord-Ouest. L’analyse des statistiques relativement aux dates d’ouverture de cette route ont permis de dénoter des dates d’ouverture très hâtives dans le cas de cinq saisons, et très tardives dans le cas de cinq autres saisons. Les années où l’ouverture est extrêmement hâtive sont distinguées par une pression au niveau de la mer irrégulièrement haute, de l’air troposphérique irrégulièrement froid, et des vents de surface du nord-ouest durant le mois de novembre précédant l’ouverture de la route. Les cinq années dont l’ouverture est extrêmement tardive sont précédées par un mois de novembre où la basse pression des Aléoutiennes y est irrégulièrement forte. Les résultats démontrent que les années où l’ouverture est extrêmement tardive sont des saisons influencées par El Niño tandis que les années dont l’ouverture est extrêmement hâtive ne sont pas systématiquement associées avec des signaux de téléconnexions. L’analyse des conditions météorologiques près de Norman Wells, associée avec les dates d’ouvertures extrêmes pour cette route, procure aux planificateurs de ces routes de l’information plus précise pour la construction de celles-ci

Influence of Mid-Latitude Cyclones on European Background Surface Ozone Investigated in Observations, MACC and MERRA-2 Reanalyses

The relationship between springtime mid-latitude cyclones and background ozone at two rural monitoring sites on the west coast of Europe -- Mace Head, Ireland and Monte Velho, Portugal -- is explored using a combination of observations and three reanalyses: 1) the European Centre for Medium-Range Weather Forecasts' (ECMWF) ERA-Interim reanalysis, 2) the Monitoring Atmospheric Composition and Climate (MACC) reanalysis and 3) NASA's Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) reanalysis. The ERA-Interim cyclone tracks are used here to establish the long-term relationship between cyclones and ozone observations (since 1988). The MACC reanalysis data set, which covers the period 2003-2012, is produced with the ECMWF integrated forecast system (IFS) model two-way coupled to a chemistry transport model (CTM). Since the MACC reanalysis uses a similar atmospheric model to ERA-Interim, MACC is used to explore the mechanisms within the case study cyclones that can influence surface ozone concentrations at Mace Head and Monte Velho. The MERRA-2 reanalysis also provides 3D distributions of ozone, although less ideal for analysis of surface ozone concentrations since MERRA-2 ozone under represents ozone variability outside the stratosphere as it does not have a detailed chemistry scheme or emission sources for the troposphere. The MERRA-2 reanalysis, which has the potential to identify more features within the cyclones as the resolution is higher than the MACC reanalysis, is used in conjunction with the MACC reanalysis to provide a measure of uncertainty to the case study analysis. We found the main source of high ozone to these two sites is from the stratosphere, which is well represented in both the MERRA-2 and the MACC reanalyses, either from direct injection into the cyclone or associated with aged airstreams from decaying downstream cyclones that can become entrained and descend toward the surface within new cyclones over the NA region

Accessibility of NASA GEOS Composition Forecasts for the Health and Air Quality Communities

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Stratospheric Intrusion-Influenced Ozone Air Quality Exceedences Investigated in MERRA-2

Ozone near the surface is harmful to human health and is a result of the photochemical reaction with both man-made and natural precursor pollutant sources. Therefore, in order to reduce near surface ozone concentrations, communities must reduce anthropogenic pollution sources. However, the injection of stratospheric ozone into the troposphere, known as a stratospheric intrusion, can also lead to concentrations of ground-level ozone exceeding air quality standards. Stratospheric intrusions are dynamical atmospheric features, however, these intrusions have been misrepresented in models and reanalyses until recently, as the features of a stratospheric intrusion are best identified in horizontal resolutions of approximately 50 km or smaller. NASA's Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) reanalysis is a publicly-available high-resolution dataset (~50 km) with assimilated ozone that characterizes stratospheric ozone on the same spatiotemporal resolution as the meteorology. We show that stratospheric intrusions that impact surface air quality are well represented in the MERRA-2 reanalysis. This is demonstrated through a case study analysis of stratospheric intrusion events which were identified by the United States Environmental Protection Agency (EPA) to impact surface ozone air quality in spring 2012 in Colorado. The stratospheric intrusions are identified in MERRA-2 by the folding of the dynamical tropopause under the jet stream and subsequent isentropic descent of dry, O3-rich stratospheric air towards the surface where ozone air quality exceedences were observed. The MERRA-2 reanalysis can support air quality agencies for more rapid identification of the impact of stratospheric air on ground-level ozone

Novel Application of NASA's GEOS-CF CO Forecasting System to ACT-America Airborne Campaign

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Using NASA's New Composition Forecast to Investigate Ozone Exceedance Events Linked with Stratospheric Intrusions

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Observing World Cities from Space: Progress and Challenges

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Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

1998-2016 ozone trends in the lower stratosphere (LS) are examined using the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) and related NASA products. After removing biases resulting from step-changes in the MERRA-2 ozone observations, a discernible negative trend of -1.67+/-0.54 Dobson units per decade (DU/decade) is found in the 10-km layer above the tropopause between 20 deg N and 60 deg N. A weaker but statistically significant trend of -1.17+/-0.33 DU/decade exists between 50 deg S and 20 deg S. In the Tropics, a positive trend is seen in a 5-km layer above the tropopause. Analysis of an idealized tracer in a model simulation constrained by MERRA-2 meteorological fields provides strong evidence that these trends are driven by enhanced isentropic transport between the tropical (20 deg S20 deg N) and extratropical LS in the past two decades. This is the first time that a reanalysis dataset has been used to detect and attribute trends in lower stratospheric ozone. Plain Language Summary. Stratospheric ozone shields the biosphere from harmful ultraviolet radiation and affects the Earths radiative budget. Observational data show evidence that concentrations of ozone in the upper stratosphere have increased in the last 15 years. This is an expected result of the implementation of the Montreal Protocol and its amendments banning emissions of ozone depleting substances into the atmosphere. The evolution of stratospheric ozone is also impacted by climate change through its dependence on temperature and circulation, which can be different at different altitudes. These effects are less well understood. This study uses NASAs data and computer models to analyze the long-term changes in ozone since 1998. It is shown that the increase in the upper stratospheric ozone has been partially offset by a small but discernible decline of ozone concentrations in the lowermost stratosphere, in qualitative agreement with one recent study. A chemistry model simulation forced by meteorological data provides strong evidence that the primary mechanism driving this negative trend is an intensification of transport of ozone-poor air from the tropics into the extratropics, indicative of a systematic change in the lower-stratospheric circulation between 1998 and 2016

NASA's High-Resolution GEOS Forecasting and Reanalysis Products: Support for TOLNet

Stratospheric intrusions (SIs) the introduction of ozone-rich stratospheric air into the troposphere have been the interest of decades of research for their link with surface ozone air quality exceedances, especially at the high elevations in the western USA in springtime; however, the impact of SIs in the remaining seasons and over the rest of the USA is less clear. We can expect MERRA-2 to realistically represent both atmospheric dynamics and composition. The operational GEOS weather forecasting system, GEOS-FP, has a similar ozone observing system to MERRA-2, while NASA's new global high-resolution air quality forecast system, GEOS-CF, combines the operational GEOS weather forecasting model with the state-of-the-science GEOS-Chem chemistry module (version 12), simulating a wide range of additional air pollutants and tracers which strengthens this detailed analysis of the intrusions and the sources for the high ozone concentrations. Using a multitude of observational datasets, including lidar, air craft, ozonesondes and air quality monitoring surface sites, in combination with the GEOS forecast and reanalysis products, we aim to provide the public with tools which are available in near-real time to enhance their capability to identify the impact of stratospheric air on surface ozone concentrations separate from anthropogenic sources. In particular, improved understanding of the connections between large-scale climate variability and local-scale dynamically-driven air quality events may support improved seasonal prediction of SI events