Using Machine Learning for Model Physics: an Overview

In the overview, a generic mathematical object (mapping) is introduced, and its relation to model physics parameterization is explained. Machine learning (ML) tools that can be used to emulate and/or approximate mappings are introduced. Applications of ML to emulate existing parameterizations, to develop new parameterizations, to ensure physical constraints, and control the accuracy of developed applications are described. Some ML approaches that allow developers to go beyond the standard parameterization paradigm are discussed.Comment: 50 pages, 3 figures, 1 tabl

Photochemistry of Triton's Atmosphere and Ionosphere

The photochemistry of 32 neutral and 21 ion species in Triton's atmosphere is considered. Parent species N2, CH4, and CO (with a mixing ratio of 3 x 10(exp -4) in our basic model) sublime from the ice with rates of 40, 208, and 0.3 g/sq cm/b.y., respectively. Chemistry below 50 km is driven mostly by photolysis of methane by the solar and interstellar medium Lyman-alpha photons, producing hydrocarbons C2H4, C2H6, and C2H2 which form haze particles with precipitation rates of 135, 28, and 1.3 g/sq cm/b.y., respectively. Some processes are discussed which increase the production of HCN (by an order of magnitude to a value of 29 g/sq cm/b.y.) and involve indirect photolysis of N2 by neutrals. Reanalysis of the measured methane profiles gives an eddy diffusion coefficient K = 4 x 10(exp 3)sq cm/s above the tropopause and a more accurate methane number density near the surface, (3.1 +/- 0.8)x IO(exp 11)/cu cm. Chemistry above 200 km is driven by the solar EUV radiation (lambda less than 1000 A) and by precipitation of magnetospheric electrons with a total energy input of 10(exp 8) W (based on thermal balance calculations). The most abundant photochemical species are N, H2, H, 0, and C. They escape with the total rates of 7.7 x 10(exp 24)/ s, 4.5 x 10(exp 25)/s, 2.4 x 10(exp 25)/s, 4.4 x 10(exp 22)/s, and 1.1 x 10(exp 24), respectively. Atomic species are transported to a region of 50-200 km and drive the chemistry there. Ionospheric chemistry explains the formation of an E region at 150-240 km with HCO(+) as a major ion, and of an F region above 240 km with a peak at 320 km and C(+) as a major ion. The ionosphere above 500 km consists of almost equal densities of C(+) and N(+) ions. The model profiles agree with the measured atomic nitrogen and electron density profiles. A number of other models with varying rate coefficients of some reactions, differing properties of the haze particles (chemically passive or active), etc., were developed. These models show that there are four basic unknown values which have strong impacts on the composition and structure of the atmosphere and ionosphere. These values and their plausible ranges are the CO mixing ratio f(sub co) = 10(exp -4) - 10(exp -3), the magnetospheric electron energy input (1 +/- 0.5) x 10(exp 8) W, the rate coefficient of charge-exchange reaction N2(+) + C(kappa) = 10(exp -11) - 10(exp -10)cu cm/s, and the ion escape velocity upsilon(sub i) approx. equals 150 cm/s

A Machine Learning Outlook: Post-processing of Global Medium-range Forecasts

Post-processing typically takes the outputs of a Numerical Weather Prediction (NWP) model and applies linear statistical techniques to produce improve localized forecasts, by including additional observations, or determining systematic errors at a finer scale. In this pilot study, we investigate the benefits and challenges of using non-linear neural network (NN) based methods to post-process multiple weather features -- temperature, moisture, wind, geopotential height, precipitable water -- at 30 vertical levels, globally and at lead times up to 7 days. We show that we can achieve accuracy improvements of up to 12% (RMSE) in a field such as temperature at 850hPa for a 7 day forecast. However, we recognize the need to strengthen foundational work on objectively measuring a sharp and correct forecast. We discuss the challenges of using standard metrics such as root mean squared error (RMSE) or anomaly correlation coefficient (ACC) as we move from linear statistical models to more complex non-linear machine learning approaches for post-processing global weather forecasts.Comment: 9 pages, 4 figures, 1 tabl

No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere, which-given methane's lifetime of several centuries-predicts an even, well mixed distribution of methane. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally

Martian dust storm impact on atmospheric H₂O and D/H observed by ExoMars Trace Gas Orbiter

Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere

Spectroscopy and photochemistry of planetary atmospheres and ionospheres: Mars, Venus, Titan, Triton and Pluto

The chemical composition of any planetary atmosphere is of fundamental importance in determining its photochemistry and dynamics in addition to its thermal balance, climate, origin and evolution. Divided into two parts, this book begins with a set of introductory chapters, starting with a concise review of the Solar System and fundamental atmospheric physics. Chapters then describe the basic principles and methods of spectroscopy, the main tool for studying the chemical composition of planetary atmospheres, and of photochemical modeling and its use in the theoretical interpretation of observational data on chemical composition. The second part of the book provides a detailed review of the carbon dioxide atmospheres and ionospheres of Mars and Venus, and the nitrogen-methane atmospheres of Titan, Triton and Pluto. Written by an expert author, this comprehensive text will make a valuable reference for graduate students, researchers and professional scientists specializing in planetary atmospheres

Russian Missions to the Moon, Venus, and Mars in 1960s

This presentation was part of the session : Historical PerspectivesSixth International Planetary Probe WorkshopFlights to the Moon, Venus, and Mars were a natural continuation of the Russian space program after the success of the first orbiters (Sputniks) in 1957-58. Sixteen spacecraft were sent to the Moon in 1959-1970 in the Soviet Union. Basic technological achievements of that program involved the first flyby of the Moon (1959), the first hard landing (1959), the first soft landing (1966), the first orbiter of the Moon (1966), and the first automatic sample return (1970). First observations of the Moon's environment (no magnetic field, no radiation belts, mascons, X-ray and gamma-ray spectroscopy of the rocks, images of the Moon, etc.), discovery of the solar wind and the first measurements of its properties, first studies of the outer radiation belt, micrometeorites and cosmic rays in the interplanetary space were among the scientific results of those missions. Insufficient reliability of the forth rocket stage (which drove a spacecraft to interplanetary orbit from the orbit around Earth) and some spacecraft subsystems badly affected the Russian flights to Venus and Mars in the early 1960s. The first spacecraft Venera was launched to Venus in 1961 and lost halfway to the target. The 2MV program presumed a landing probe to Venus and flyby of Mars with launch in 1962. The Mars 1 probe was lost halfway to Mars. The 3MV program involved a landing probe to Venus and flybys of Venus and Mars using similar spacecraft with launch in 1964-1965. The spacecraft for Mars was not ready by the launch time in 1964 and was sent to the Moon as Zond 3 in 1965. Veneras 2 and 3 were launched in 1965 and lost near Venus. All later Russian missions to Venus were successful. Venera 4 (1967) was the first soft entry probe that made observations down to 22 km and flyby of Venus. Veneras 5 and 6 (1969) were alive down to 17 km, and Venera 7 (1970) made the first soft landing on Venus. Scientific return of the early Venera missions included studies of the interplanetary space at the cruise phase and the first direct measurements of pressure, density, and temperature profiles in the atmosphere and its chemical composition. Atomic O and H were detected and observed in the Venus' upper atmosphere as well. The Mars 1969 mission involved a new large spacecraft and a new powerful booster. However, the mission crashed at the launch phase. The author was technically responsible for the surface phase state and gamma-ray detector at the Venus lander of 2MV, the photometer at the Venus lander of 3MV (Venera 3), electronics of the IR radiometer at Luna 13 (1966), and the ultraviolet spectrometer at the Venera 2, Zond 3, and Mars 1969 missions. This UV spectrometer was also used at the Cosmos 65 and Cosmos 121 orbiters in 1965 and 1966 and returned the first study of the global ozone distribution

Atmospheric photochemistry

International audienc

Photochemistry of Pluto's Atmosphere

This work include studies of two problems: (1) Modeling thermal balance, structure. and escape processes in Pluto's upper atmosphere. This study has been completed in full. A new method, of analytic solution for the equation of hydrodynamic flow from in atmosphere been developed. It was found that the ultraviolet absorption by methane which was previously ignored is even more important in Pluto's thermal balance than the extreme ultraviolet absorption by nitrogen. Two basic models of the lower atmosphere have been suggested, with a tropopause and a planetary surface at the bottom of the stellar occultation lightcurve, respectively, Vertical profiles, of temperature, density, gas velocity, and the CH4 mixing ratio have been calculated for these two models at low, mean, and high solar activity (six models). We prove that Pluto' " s atmosphere is restricted to 3060-4500 km, which makes possible a close flyby of future spacecraft. Implication for Pluto's evolution have also been discussed. and (2) Modeling of Pluto's photochemistry. Based on the results of (1), we have made some changes in the basic continuity equation and in the boundary conditions which reflect a unique can of hydrodynamic escape and therefore have not been used in modeling of other planetary atmospheres. We model photochemistry of 44 neutral and 23 ion species. This work required solution of a set of 67 second-order nonlinear ordinary differential equations. Two models have been developed. Each model consists of the vertical profiles for 67 species, their escape and precipitation rates. These models predict the chemical structure and basic chemical processes in the current atmosphere and possible implication of these processes for evolution. This study has also been completed in full