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arXiv2011

Microburst nowcasting applications of GOES

Recent testing and validation have found that the Geostationary Operational Environmental Satellite (GOES) microburst products are effective in the assessment and short-term forecasting of downburst potential and associated wind gust magnitude. Two products, the GOES sounder Microburst Windspeed Potential Index (MWPI) and a new bi-spectral GOES imager brightness temperature difference (BTD) product have demonstrated capability in downburst potential assessment. In addition, a comparison study between the GOES-R Convective Overshooting Top (OT) Detection and MWPI algorithms has been completed for cases that occurred during the 2007 to 2009 convective seasons over the southern Great Plains. Favorable results of the comparison study include a statistically significant negative correlation between the OT minimum temperature and MWPI values and associated measured downburst wind gust magnitude. The negative functional relationship between the OT parameters and wind gust speed highlights the importance of updraft strength, realized by large CAPE, in the generation of heavy precipitation and subsequent intense convective downdraft generation. This paper provides an updated assessment of the GOES MWPI and GOES BTD algorithms, presents case studies demonstrating effective operational use of the microburst products, and presents results of a cross comparison study of the GOES-R overshooting top (OT) detection algorithm over the United States Great Plains region.

physics.ao-ph↗

arXiv2011

Misure quantitative del seeing atmosferico

A simple technique of measurement of seeing in daytime and nighttime, based upon drift-scan observations, is presented, along with observational examples. This experience can be repeated easily in classroom contexts.

astro-ph.IM↗

arXiv2011

3D effects in the dynamics of oceanic rogue waves: A numerical study

Recent results of numerical simulations of fully nonlinear evolutionary equations for long-crested deep-water waves are discussed, where formation of extreme waves was observed. Several examples demonstrate that three-dimensionality of the fluid motion has an essential influence on the process of rogue wave formation. In particular, in the presence of elongate wave groups, the most tall extreme waves occur when in an initial state the wave fronts were oriented obliquely to the direction of the group. An "optimal" angle, resulting in the highest rogue waves, depends on initial wave amplitude and group width, and it is about 18-28 degrees in a practically important range of parameters. Besides that, the mechanism of spatial-temporal focusing on a random wave background has been simulated for several values of nonlinearity.

physics.ao-ph↗

arXiv2011

Ignition from a Fire Perimeter in a WRF Wildland Fire Model

The current WRF-Fire model starts the fire from a given ignition point at a given time. We want to start the model from a given fire perimeter at a given time instead. However, the fuel balance and the state of the atmosphere depend on the history of the fire. The purpose of this work is to create an approximate artificial history of the fire based on the given fire perimeter and time and an approximate ignition point and time. Replaying the fire history then establishes a reasonable fuel balance and outputs heat fluxes into the atmospheric model, which allow the atmospheric circulation to develop. Then the coupled atmosphere-fire model takes over. In this preliminary investigation, the ignition times in the fire area are calculated based on the distance from the ignition point to the perimeter, assuming that the perimeter is convex or star-shaped. Simulation results for an ideal example show that the fire can continue in a natural way from the perimeter. Possible extensions include algorithms for more general perimeters and running the fire model backwards in time from the perimeter to create a more realistic history. The model used extends WRF-Fire and it is available from openwfm.org.

physics.ao-ph↗

arXiv2011

Universal constants and equations of turbulent motion

In the spirit of Prandtl's conjecture of 1926, for turbulence at high Reynolds number we present an analogy with the kinetic theory of gases, with dipoles made of quasi-rigid and 'dressed' vortex tubes as frictionless, incompressible but deformable quasi-particles. Their movements are governed by Helmholtz' elementary vortex rules applied locally. A contact interaction or 'collision' leads either to random scatter of a trajectory or to the formation of two likewise rotating, fundamentally unstable whirls forming a dissipative patch slowly rotating around its center of mass which is almost at rest. This approach predicts von Karman's constant as 1/sqrt(2 pi) = 0.399 and the spatio-temporal dynamics of energy-containing time and length scales controlling turbulent mixing [Baumert 2009]. A link to turbulence spectra was missing so far. In the present paper it is shown that the above image of random vortex-dipole movements is compatible with Kolmogorov's turbulence spectra if dissipative patches, beginning as two likewise rotating eddies, evolve locally into a space-filling bearing in the sense of Herrmann [1990], i.e. into an "Apollonian gear". Its parts and pieces are incompressible and flexibly deformable vortex tubes which are frictionless, excepting the dissipative scale of size zero. For steady and locally homogeneous conditions our approach predicts the dimensionless pre-factor in the 3D Eulerian wavenumber spectrum as [(4 pi)^2/3]/3 = 1.8, and in the Lagrangian frequency spectrum as 2. Our derivations rest on geometry, methods from many-particle physics, and on elementary conservation laws.

physics.flu-dyn↗

arXiv2011

Ensemble regional data assimilation using joint states

We propose a data assimilation scheme that produces the analyses for a global and an embedded limited area model simultaneously, considering forecast information from both models. The purpose of the proposed approach is twofold. First, we expect that the global analysis will benefit from incorporation of information from the higher resolution limited area model. Second, our method is expected to produce a limited area analysis that is more strongly constrained by the large scale flow than a conventional limited area analysis. The proposed scheme minimizes a cost function in which the control variable is the joint state of the global and the limited area models. In addition, the cost function includes a constraint term that penalizes large differences between the global and the limited area state estimates. The proposed approach is tested by idealized experiments, using `toy' models introduced by Lorenz in 2005. The results of these experiments suggest that the proposed approach improves the global analysis within and near the limited area domain and the regional analysis near the lateral boundaries. These analysis improvements lead to forecast improvements in both the global and the limited area models.

nlin.CD↗

arXiv2011

United Nations Basic Space Science Initiative: 2011 Status Report on the International Space Weather Initiative

The UNBSSI is a long-term effort for the development of astronomy and space science through regional and international cooperation in this field on a worldwide basis. A series of workshops on BSS was held from 1991 to 2004 (India 1991, Costa Rica and Colombia 1992, Nigeria 1993, Egypt 1994, Sri Lanka 1995, Germany 1996, Honduras 1997, Jordan 1999, France 2000, Mauritius 2001, Argentina 2002, and China 2004; http://www.seas.columbia.edu/~ah297/un-esa/) and addressed the status of astronomy in Asia and the Pacific, Latin America and the Caribbean, Africa, and Western Asia. One major recommendation that emanated from these workshops was the establishment of astronomical facilities in developing nations for research and education programmes at the university level. Such workshops on BSS emphasized the particular importance of astrophysical data systems and the virtual observatory concept for the development of astronomy on a worldwide basis. Pursuant to resolutions of the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) and its Scientific and Technical Subcommittee, since 2005, these workshops focused on the International Heliophysical Year 2007 (UAE 2005, India 2006, Japan 2007, Bulgaria 2008, Ro Korea 2009; http://www.unoosa.org/oosa/SAP/bss/ihy2007/index.html). Starting in 2010, the workshops focus on the International Space Weather Initiative (ISWI) as recommended in a three-year-work plan as part of the deliberations of UNCOPUOS (http://www.stil.bas.bg/ISWI/). Workshops on the ISWI have been scheduled to be hosted by Egypt in 2010 for Western Asia, Nigeria in 2011 for Africa, and Ecuador in 2012 for Latin America and the Caribbean. Currently, 14 IHY/ISWI instrument arrays with > 600 instruments are operational in 95 countries.

physics.space-ph↗

arXiv2011

Frequency Characteristics Of Acoustic-Gravity Eigenwaves Of The Nonadiabatic Atmosphere

The main objective of the given work consists in the account of the basic mechanisms, which decline processes in atmosphere from adiabaticity approach, and in the study of effect non-adiabaticity on the swing of eigenmodes of atmosphere at various altitudes. The dispersion equation is solved, dispersion curves for acoustic and gravity branches are explored. The increment of growth of eigenmodes at various altitudes of atmosphere is explored. Frequencies (real part) both for acoustic, and for gravity branches acoustic-gravity waves (AGW) in nonadiabatic atmosphere, coinciding with frequencies of the adiabatic model for the same wave vectors at low altitudes, smoothly decrease with altitude. It leads to decrease of a phase velocity for both branches at larger altitudes in a real atmosphere in comparison with predicted by the adiabatic model.

physics.plasm-ph↗

arXiv2012

Scientific Case for Avoiding Dangerous Climate Change to Protect Young People and Nature

Global warming due to human-made gases, mainly CO2, is already 0.8°C and deleterious climate impacts are growing worldwide. More warming is 'in the pipeline' because Earth is out of energy balance, with absorbed solar energy exceeding planetary heat radiation. Maintaining a climate that resembles the Holocene, the world of stable shorelines in which civilization developed, requires rapidly reducing fossil fuel CO2 emissions. Such a scenario is economically sensible and has multiple benefits for humanity and other species. Yet fossil fuel extraction is expanding, including highly carbon-intensive sources that can push the climate system beyond tipping points such that amplifying feedbacks drive further climate change that is practically out of humanity's control. This situation raises profound moral issues as young people, future generations, and nature, with no possibility of protecting their future well-being, will bear the principal consequences of actions and inactions of today's adults.

physics.ao-ph↗

arXiv2012

Hamiltonian description and traveling waves of the spatial Dysthe equations

The spatial version of the fourth-order Dysthe equations describe the evolution of weakly nonlinear narrowband wave trains in deep waters. For unidirectional waves, the hidden Hamiltonian structure and new invariants are unveiled by means of a gauge transformation to a new canonical form of the evolution equations. A highly accurate Fourier-type spectral scheme is developed to solve for the equations and validate the new conservation laws, which are satisfied up to machine precision. Further, traveling waves are numerically investigated using the Petviashvili method. It is found that their collision appears inelastic, suggesting the non-integrability of the Dysthe equations.

physics.class-ph↗

arXiv2011

Comment on "Triggering Rogue Waves in Opposing Currents"

The authors of a recent Letter ([1] M. Onorato, D. Proment, and A. Toffoli, Phys. Rev. Lett. 107, 184502 (2011)) based their study of rogue waves in nonuniform currents on a modified nonlinear Schrödinger equation (NLSE; see Eq.(1) in [1]). However, I show here that equation is not correct. It gives wrong solutions even in the first order on the supposedly small parameter $U/c_{\rm g}$, where $U(x)$ is a current, and $c_{\rm g}=g/(2 ω)$ [here $ω$ is a mean frequency of a quasi-monochromatic wave train, and $g$ is the gravity acceleration]. I also suggest an accurate variant of NLSE, valid in the presence of a large-scale nonuniform current under condition $(1+4ωU/g) \gtrsim 0.2$.

physics.flu-dyn↗

arXiv2012

New observations in transient hydrodynamic perturbations. Frequency jumps, intermediate term and spot formation

Sheared incompressible flows are usually considered non-dispersive media. As a consequence, the frequency evolution in transients has received much less attention than the wave energy density or growth factor. By carrying out a large number of long term transient simulations for longitudinal, oblique and orthogonal perturbations in the plane channel and wake flows, we could observe a complex time evolution of the frequency. The complexity is mainly associated to jumps which appear quite far along within the transients. We interpret these jumps as the transition between the early transient and the beginning of an intermediate term that reveals itself for times large enough for the influence of the fine details of the initial condition to disappear. The intermediate term leads to the asymptotic exponential state and has a duration one order of magnitude longer than the early term, which indicates the existence of an intermediate asymptotics. Since after the intermediate term perturbations die out or blowup, the mid-term can be considered as the most probable state in the perturbation life. Long structured transients can be related to the spot patterns commonly observed in subcritical transitional wall flows. By considering a large group of 3D waves in a narrow range of wavenumbers, we superposed them in a finite temporal window with oblique and longitudinal waves randomly delayed with respect to an orthogonal wave which is supposed to sustain the spot formation with its intense transient growth. We show that in this way it is possible to recover the linear initial evolution of the pattern characterized by the presence of longitudinal streaks. We also determined the asymptotic frequency and phase speed wavenumber spectra for the channel and wake flows. The mild dispersion observed can in part explain the different propagation speeds of the backward and forward fronts of the spot.

physics.flu-dyn↗

arXiv2013

Invariant parameterization and turbulence modeling on the beta-plane

Invariant parameterization schemes for the eddy-vorticity flux in the barotropic vorticity equation on the beta-plane are constructed and then applied to turbulence modeling. This construction is realized by the exhaustive description of differential invariants for the maximal Lie invariance pseudogroup of this equation using the method of moving frames, which includes finding functional bases of differential invariants of arbitrary order, a minimal generating set of differential invariants and a basis of operators of invariant differentiation in an explicit form. Special attention is paid to the problem of two-dimensional turbulence on the beta-plane. It is shown that classical hyperdiffusion as used to initiate the energy-enstrophy cascades violates the symmetries of the vorticity equation. Invariant but nonlinear hyperdiffusion-like terms of new types are introduced and then used in the course of numerically integrating the vorticity equation and carrying out freely decaying turbulence tests. It is found that the invariant hyperdiffusion scheme is close to but not exactly reproducing the 1/k shape of energy spectrum in the enstrophy inertial range. By presenting conservative invariant hyperdiffusion terms, we also demonstrate that the concepts of invariant and conservative parameterizations are consistent.

math-ph↗

arXiv2012

Infrared/Terahertz double resonance spectroscopy of CH3F and CH3Cl at atmospheric pressure

A new method for highly selective remote sensing of atmospheric trace polar molecular gases is described. Based on infrared/terahertz double resonance spectroscopic techniques, the molecule- specific coincidence between the lines of a CO2 laser and rotational-vibrational molecular absorption transitions provide two dimensions of recognition specificity: infrared coincidence frequency and the corresponding terahertz frequency whose absorption strength is modulated by the laser. Atmospheric pressure broadening expands the molecular recognition "specificity matrix" by simultaneously relaxing the infrared coincidence requirement and strengthening the corresponding terahertz signature. Representative double resonance spectra are calculated for prototypical molecules CH3F and CH3Cl and their principal isotopomers, from which a heuristic model is developed to estimate the specificity matrix and double resonance signature strength for any polar molecule.

physics.atom-ph↗

arXiv2017

Principal component proxy tracer analysis

We introduce a powerful method for dynamical reconstruction of long-lived tracers such as ozone. It works by correlating the principal components of a matrix representation of the tracer dynamics with a series of sparse measurements. The method is tested on the 500 K isentropic surface using a simulated tracer and with ozone measurements from the Polar Aerosol and Ozone Measurement (POAM) III satellite instrument. The Lyapunov spectrum is measured and used to quantify the lifetime of each principal component. Using a 60 day lead time and five (5) principal components, cross validation of the reconstructed ozone and comparison with ozone sondes return root-mean-square errors of 0.20 ppmv and 0.47 ppmv, respectively.

physics.ao-ph↗

arXiv2012

Microwave emissivity of fresh water ice--Lake ice and Antarctic ice pack--Radiative transfer simulations versus satellite radiances

Microwave emissivity models of sea ice are poorly validated empirically. Typical validation studies involve using averaged or stereotyped profiles of ice parameters against averaged radiance measurements. Measurement sites are rarely matched and even less often point-by-point. Because of saline content, complex permittivity of sea ice is highly variable and difficult to predict. Therefore, to check the validity of a typical, plane-parallel, radiative-transfer-based ice emissivity model, we apply it to fresh water ice instead of salt-water ice. Radiance simulations for lake ice are compared with measurements over Lake Superior from the Advanced Microwave Scanning Radiometer on EOS (AMSR-E). AMSR-E measurements are also collected over Antarctic icepack. For each pixel, a thermodynamic model is driven by four years of European Center for Medium Range Weather Forecasts (ECMWF) reanalysis data and the resulting temperature profiles used to drive the emissivity model. The results suggest that the relatively simple emissivity model is a good fit to the data. Both cases, however, show large discrepencies whose most likely explanation is scattering both within the ice sheet as well as by cloudy atmospheres. Scattering is neglected by the model. Further work is needed to refine the scattering component of ice emissivity models and to generate accurate estimates of complex permittivities within sea ice.

physics.ao-ph↗

arXiv2012

Comments on the Paper "Earth's energy imbalance and implications" by J. Hansen, M. Sato, P. Kharecha, and K. von Schuckmann

In our comments we explicitly acknowledge the attempt of Hansen et al. to assess various uncertainties inherent in geophysical data being based on different measuring concepts and observation methods. However, with regard to the planetary energy budget, this paper offers some vulnerable points. We will focus our comments on these vulnerable points only. We will show that the energy imbalance of the entire Earth-atmosphere system is, indeed, based on these inherent uncertainties. We will demonstrate that the accuracy in the quantification of the global energy flux budget as claimed by Hansen et al. is, by far, not achievable in case of the entire Earth-atmosphere system. Using the value of the solar constant of S_0 = 1361 W/m^2 recently determined on the basis of total-solar-irradiance (TSI) observation by three different satellite projects (ACRIMSAT/ACRIM3 launched in 2000, SORCE/TIM launched in 2003, and PICARD/PREMOS launched in 2010) we will document that the planetary energy imbalance of F = 0.58 +/- 0.15 W/m^2 calculated by Hansen et al. does not exist. Consequently, the implications related to this planetary energy imbalance have no basis.

physics.ao-ph↗

arXiv2012

The study of ground-level ozone in Kiev and its impact on public health

Ground-level ozone in Kiev for an episode of its high concentration in August 2000 was simulated with the model of the urban air pollution UAM-V (Urban Airshed Model). The study of total ozone over Kiev and its concentration changes with height in the troposphere is made on the basis of ground-based observations with the infrared Fourier spectrometer at the Main Astronomical Observatory of National Academy of Sciences of Ukraine as a part of the ESA-NIVR-KNMI no 2907. In 2008 the satellite Aura-OMI data OMO3PR on the atmosphere ozone profiles became available. Beginning in 2005, these data include the ozone concentration in the lower layer of the atmosphere and can be used for the evaluation of the ground-level ozone concentrations in all cities of Ukraine. Some statistical investigation of ozone air pollution in Kiev and medical statistics data on respiratory system was carried out with the application of the "Statistica" package. The regression analysis, prognostic regression simulation, and retrospective prognosis of the epidemiological situation with respect to respiratory system pathologies in Kiev during 2000-2007 were performed.

astro-ph.EP↗