282 research outputs found
Explainable Offline-Online Training of Neural Networks for Parameterizations: A 1D Gravity Wave-QBO Testbed in the Small-data Regime
There are different strategies for training neural networks (NNs) as
subgrid-scale parameterizations. Here, we use a 1D model of the quasi-biennial
oscillation (QBO) and gravity wave (GW) parameterizations as testbeds. A
12-layer convolutional NN that predicts GW forcings for given wind profiles,
when trained offline in a big-data regime (100-years), produces realistic QBOs
once coupled to the 1D model. In contrast, offline training of this NN in a
small-data regime (18-months) yields unrealistic QBOs. However, online
re-training of just two layers of this NN using ensemble Kalman inversion and
only time-averaged QBO statistics leads to parameterizations that yield
realistic QBOs. Fourier analysis of these three NNs' kernels suggests why/how
re-training works and reveals that these NNs primarily learn low-pass,
high-pass, and a combination of band-pass filters, consistent with the
importance of both local and non-local dynamics in GW propagation/dissipation.
These findings/strategies apply to data-driven parameterizations of other
climate processes generally
Evaporation of alcohol droplets on surfaces in moist air
Droplets of alcohol-based formulations are common in applications from sanitising sprays to printing inks. However, our understanding of the drying dynamics of these droplets on surfaces and the influence of ambient humidity is still very limited. Here, we report the drying dynamics of picoliter droplets of isopropyl alcohol (IPA) deposited on a surface under controlled humidity. Condensation of water vapour in the ambient environment onto alcohol droplets leads to unexpectedly complex drying behaviour. As relative humidity (RH) increases, we observed a variety of phenomena including enhanced spreading, non-monotonic changes in the drying time, the formation of pancake-like shapes that suppress the coffee-ring effect, and the formation of water-rich films around an alcohol-rich drop. We developed a lubrication model that accounts for the coupling between the flow field within the drop, the shape of the drop, and the vapor concentration field. The model reproduces many of the experimentally observed morphological and dynamic features, revealing the presence of unusually large spatial compositional gradients within the evaporating droplet and surface-tension-gradient-driven flows arising from water condensation/evaporation at the surface of the droplet. One unexpected feature from the simulation is that water can evaporate and condense concurrently in different parts of the drop, providing fundamental insights that simpler models based on average fluxes lack. We further observed rim instabilities at higher RH that are well-described by a model based on the Rayleigh-Plateau instability. Our findings have implications for the testing and use of alcohol-based disinfectant sprays and printing inks
Characteristics of Gravity Waves in Opposing Phases of the QBO: A Reanalysis Perspective with ERA5
ERA5 data for the period of 1979-2019 are used as a basis for investigating
the properties of gravity waves as they disperse and propagate upward through
the stratosphere during opposing phases of the QBO. Two-sided zonal
wavenumber-frequency spectra of vertical velocity in the stratosphere exhibit
distinctive gravity wave signatures. Consistent with theory, westward
propagating waves tend to be suppressed during the easterly QBO phase and
eastward propagating waves tend to be suppressed during the westerly phase.
Cospectra of the vertical flux of zonal momentum also show significant
asymmetries between eastward and westward propagating waves during opposing QBO
phases. Phase speed spectra of the vertical flux of momentum are indicative of
a strong dissipation of westward propagating gravity waves during the easterly
phase and vice versa; i.e., a selective "wind filtering" of the waves as they
propagate upward. The three-dimensional structure of the gravity waves is
revealed by compositing. In the absence of a background zonal flow, the waves
radiate outward and upward from their respective reference grid points in
concentric rings. When a zonal flow is present, the rings are amplified and
compressed upstream of the source and attenuated and stretched downstream of
it, such that they assume the form of arcs. These results serve to confirm the
applicability of the mechanism proposed by Lindzen and Holton (1968) to explain
the downward propagation of the QBO. The QBO also influences the spectrum of
gravity waves in ERA5 at 100 hPa, below the layer in which wind-filtering
occurs
N=1 de Sitter Supersymmetry Algebra
Recalling the universal covering group of de Sitter, the transformation
properties of the spinor fields and , in the ambient
space notation, are presented in this paper. The charge conjugation symmetry of
the de Sitter spinor field is then discussed in the above notation. Using this
spinor field and charge conjugation, de Sitter supersymmetry algebra in the
ambient space notation has been established. It is shown that a novel
dS-superalgebra can be attained by the use of spinor field and charge
conjugation in the ambient space notation.Comment: 8 pages, LaTeX, some details adde
Simultaneous use of two pectoralis flaps after total laryngopharyngectomy and total glossectomy � A case report study
The defects of the head and neck region present major challenges, but successful cosmetic and functional results have been achieved with both local and free tissue flaps. We report a case of advanced laryngopharyngeal carcinoma with extension to tongue and cervical esophagus. The subject had a history of previous radiotherapy, so he underwent salvage surgery. Reconstruction surgery for total laryngopharyngectomy and total glossectomy with total esophagectomy was performed using gastric pull up and two pectoralis major flaps. © 202
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