Further Results on Moist Nearly Neutral Flow over a Ridge

2006 ◽  
Vol 63 (11) ◽  
pp. 2881-2897 ◽  
Author(s):  
M. M. Miglietta ◽  
R. Rotunno
Keyword(s):  
Coriolis Force ◽  
Numerical Solutions ◽  
Wrf Model ◽  
Rainfall Rate ◽  
Experimental Conditions ◽  
Available Water Content ◽  
Warm Rain ◽  
Temperature Regimes ◽  
Neutral Flow ◽  
Microphysical Processes

Abstract In a recent study, the authors performed numerical simulations of moist nearly neutral flows over a ridge using the Weather Research and Forecasting (WRF) Model in a regime where the Coriolis force can be neglected and with the simple Kessler (warm rain) microphysical scheme. In the present work, further numerical solutions using more general and realistic experimental conditions are discussed. The upstream-propagating disturbance, which was found in the author’s previous study to desaturate the initially saturated sounding for intermediate mountain heights, is present for all the simulations with taller mountains considered in the present work. The inclusion of the Coriolis force however suppresses the upwind propagation of the dry region and weakens the downstream development of convective cells. The sensitivity to different microphysical schemes has also been investigated. The simple Kessler scheme was compared with a more complete scheme, by Lin et al., which includes ice species. Some differences between the warm-rain-only and ice-microphysics simulations emerge mainly as a consequence of the different distributions of initial cloud water needed to produce a steady-state environmental flow. The effects of the different microphysical schemes on the rainfall rate have also been analyzed, with significant differences between them emerging in the case of narrower mountains. Finally, the sensitivity of the rainfall to the surface temperature has been studied, showing that for higher surface temperatures, the rainfall rate can be smaller although the available water content is larger, as a consequence of the differing microphysical processes activated in the different temperature regimes.

Atomic Imaging of Crystals using Large-Angle Electron Scattering in STEM

1990 ◽  
Vol 48 (1) ◽  
pp. 74-75
Author(s):  
D.E. Jesson ◽  
S. J. Pennycook
Keyword(s):  
Wave Function ◽  
Electron Scattering ◽  
Numerical Solutions ◽  
Large Angle ◽  
Real Space ◽  
High Angle ◽  
Analytical Treatment ◽  
Order Zero ◽  
Experimental Conditions ◽  
Ewald Sphere

It is well known that conventional atomic resolution electron microscopy is a coherent imaging process best interpreted in reciprocal space using contrast transfer function theory. This is because the equivalent real space interpretation involving a convolution between the exit face wave function and the instrumental response is difficult to visualize. Furthermore, the crystal wave function is not simply related to the projected crystal potential, except under a very restrictive set of experimental conditions, making image simulation an essential part of image interpretation. In this paper we present a different conceptual approach to the atomic imaging of crystals based on incoherent imaging theory. Using a real-space analysis of electron scattering to a high-angle annular detector, it is shown how the STEM imaging process can be partitioned into components parallel and perpendicular to the relevant low index zone-axis.It has become customary to describe STEM imaging using the analytical treatment developed by Cowley. However, the convenient assumption of a phase object (which neglects the curvature of the Ewald sphere) fails rapidly for large scattering angles, even in very thin crystals. Thus, to avoid unpredictive numerical solutions, it would seem more appropriate to apply pseudo-kinematic theory to the treatment of the weak high angle signal. Diffraction to medium order zero-layer reflections is most important compared with thermal diffuse scattering in very thin crystals (<5nm). The electron wave function ψ(R,z) at a depth z and transverse coordinate R due to a phase aberrated surface probe function P(R-RO) located at RO is then well described by the channeling approximation;

Pathways to the Production of Precipitating Hydrometeors and Tropical Cyclone Development

2016 ◽  
Vol 144 (6) ◽  
pp. 2395-2420 ◽  
Author(s):  
J.-W. Bao ◽  
S. A. Michelson ◽  
E. D. Grell
Keyword(s):  
Tropical Cyclone ◽  
Wrf Model ◽  
Cloud Microphysics ◽  
Weather Research And Forecasting ◽  
Rapid Intensification ◽  
Latent Heating ◽  
Vertical Distributions ◽  
Double Moment ◽  
Microphysical Processes ◽  
Definition Of

Abstract Pathways to the production of precipitation in two cloud microphysics schemes available in the Weather Research and Forecasting (WRF) Model are investigated in a scenario of tropical cyclone intensification. Comparisons of the results from the WRF Model simulations indicate that the variation in the simulated initial rapid intensification of an idealized tropical cyclone is due to the differences between the two cloud microphysics schemes in their representations of pathways to the formation and growth of precipitating hydrometeors. Diagnoses of the source and sink terms of the hydrometeor budget equations indicate that the major differences in the production of hydrometeors between the schemes are in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes, such as accretion growth and sedimentation. These differences lead to different horizontally averaged vertical profiles of net latent heating rate associated with significantly different horizontally averaged vertical distributions and production rates of hydrometeors in the simulated clouds. Results from this study also highlight the possibility that the advantage of double-moment formulations can be overshadowed by the uncertainties in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes.

Effect of pinealectomy on the testicular response of the freshwater snake Natrix piscator to different environmental factors

1989 ◽  
Vol 67 (10) ◽  
pp. 2352-2357 ◽  
Author(s):  
C. Haldar ◽  
R. Pandey
Keyword(s):  
High Temperature ◽  
Pineal Gland ◽  
High Humidity ◽  
Testicular Function ◽  
Experimental Conditions ◽  
Gland Weight ◽  
Tropical Water ◽  
Water Snake ◽  
Temperature Regimes ◽  
Testicular Weight

The effects of different humidity, photoperiod, and temperature regimes on the testicular function of the tropical water snake Natrix piscator were investigated in both sham-operated and pinealectomized snakes. Moderate humidity (50 ± 5%) had no effect on the testis, but high humidity (85 ± 5%) increased the testicular weight and activity of sham-operated snakes after 3, 6, and 9 weeks. Exposures to 14L:10D or 24L:0D and high temperature (42 ± 2 °C) inhibited testicular weight and activity in sham-operated snakes, whereas exposure to 10L:14D or 0L:24D and a low temperature (20 ± 2 °C) had no effect. Pinealectomized snakes did not respond to any of these experimental conditions, but their testicular weight remained the same as that of the pinealectomized controls under natural environmental conditions. The pineal gland showed an opposite response to that of the testes. Pineal gland weight decreased under high humidity and increased under 14L:10D, 24L:0D, and high temperature. These findings suggest that the ecofactors humidity, photoperiod, and temperature play a role in the regulation of testicular function in this snake, and that the pineal gland is implicated in the mediation of these factors.

scholarly journals Internal Gravity Waves in a Saturated Moist Neutral Atmosphere

2013 ◽  
Vol 70 (12) ◽  
pp. 3693-3709 ◽  
Author(s):  
David J. Muraki ◽  
Richard Rotunno
Keyword(s):  
Numerical Solutions ◽  
Internal Gravity Waves ◽  
Analytic Solutions ◽  
Neutral Atmosphere ◽  
Atmospheric Flow ◽  
Start Up ◽  
Exact Analytic Solutions ◽  
Downward Displacement ◽  
Neutral Flow ◽  
Saturated Atmosphere

Abstract This work is motivated by an unusual feature associated with the start-up of a moist nearly neutral atmospheric flow over a mountain ridge that was previously observed in a full-physics numerical model. In that study, the upstream propagation of a wave of subsidence precluded the establishment of upward-displaced and saturated flow that might be expected upstream of the topography. This phenomenon was hypothesized to be a consequence of the peculiar property of saturated moist neutral flow: an upward air parcel displacement produces zero buoyancy, while a downward displacement desaturates the air parcel and produces a positive buoyancy anomaly. In the present study, this hypothesis is confirmed within numerical solutions to a reduced system of equations that incorporates the saturated-atmosphere property in a particularly simple manner. The relatively uncomplicated nature of these solutions motivates the numerical solution of a further simplified initial-value problem for both nonhydrostatic and hydrostatic flow. Exact analytic solutions are developed for the latter hydrostatic case, which explains the upstream-propagating wave of subsidence as a shock phenomenon.

scholarly journals A New Bulk Microphysical Scheme That Includes Riming Intensity and Temperature-Dependent Ice Characteristics

2011 ◽  
Vol 139 (3) ◽  
pp. 1013-1035 ◽  
Author(s):  
Yanluan Lin ◽  
Brian A. Colle
Keyword(s):  
Wrf Model ◽  
Computationally Efficient ◽  
Fall Velocity ◽  
Surface Precipitation ◽  
Ice Particles ◽  
Microphysical Processes ◽  
Empirical Coefficients ◽  
Oregon Cascades ◽  
Microphysical Parameterization ◽  
Ice Water

Abstract A new bulk microphysical parameterization (BMP) scheme is presented that includes a diagnosed riming intensity and its impact on ice characteristics. As a result, the new scheme represents a continuous spectrum from pristine ice particles to heavily rimed particles and graupel using one prognostic variable [precipitating ice (PI)] rather than two separate variables (snow and graupel). In contrast to most existing parameterization schemes that use fixed empirical relationships to describe ice particles, general formulations are proposed to consider the influences of riming intensity and temperature on the projected area, mass, and fall velocity of PI particles. The proposed formulations are able to cover the variations of empirical coefficients found in previous observational studies. The new scheme also reduces the number of parameterized microphysical processes by ∼50% as compared to conventional six-category BMPs and thus it is more computationally efficient. The new scheme (called SBU-YLIN) has been implemented in the Weather Research and Forecasting (WRF) model and compared with three other schemes for two events during the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) over the central Oregon Cascades. The new scheme produces surface precipitation forecasts comparable to more complicated BMPs. The new scheme reduces the snow amounts aloft as compared to other WRF schemes and compares better with observations, especially for an event with moderate riming aloft. Sensitivity tests suggest both reduced snow depositional growth rate and more efficient fallout due to the contribution of riming to the reduction of ice water content aloft in the new scheme, with a larger impact from the partially rimed snow and fallout.

On the Impact of WRF Model Vertical Grid Resolution on Midwest Summer Rainfall Forecasts

2009 ◽  
Vol 24 (2) ◽  
pp. 575-594 ◽  
Author(s):  
Eric A. Aligo ◽  
William A. Gallus ◽  
Moti Segal
Keyword(s):  
Negative Impact ◽  
Wrf Model ◽  
Summer Rainfall ◽  
Grid Resolution ◽  
Illustrative Case ◽  
Rainfall Thresholds ◽  
Vertical Grid ◽  
Microphysical Processes ◽  
The Impact ◽  
Melting Level

Abstract Weather Research and Forecast (WRF) model exploratory sensitivity simulations were performed to determine the impact of vertical grid resolution (VGR) on the forecast skill of Midwest summer rainfall. Varying the VGR indicated that a refined VGR, while adopting the widely used North America Regional Reanalysis (NARR) for initial and lateral boundary conditions, does not necessarily result in a consistent improvement in quantitative precipitation forecasts (QPFs). When averaged over a variety of microphysical schemes in an illustrative case, equitable threat score (ETS) and bias values actually worsened with a greater overpredicted rainfall for half of the rainfall thresholds when the VGR was refined. Averaged over strongly forced cases, ETS values worsened for all rainfall thresholds while biases mostly increased, indicating a further overprediction of rainfall when the number of levels was increased. Skill improved, however, for all rainfall thresholds when the resolution above the melting level was increased. Skill also improved for most rainfall thresholds when the resolution in the surface layer was increased, which is attributed to better-resolved surface turbulent momentum and thermal fluxes. Likewise, a refined VGR resulted in improvements in weakly forced cases, which are governed mostly by thermodynamic forcing and are sensitive to vertical profiles of temperature and moisture. Application of the factor separation method suggested that the refined VGR more frequently had a negative impact on skill through the interaction between lower-atmospheric processes and microphysical processes above the melting level.

scholarly journals Impact of Microphysics Parameterizations on Simulations of the 27 October 2010 Great Salt Lake–Effect Snowstorm

2015 ◽  
Vol 30 (1) ◽  
pp. 136-152 ◽  
Author(s):  
John D. McMillen ◽  
W. James Steenburgh
Keyword(s):  
Salt Lake ◽  
Weather Prediction ◽  
Great Salt Lake ◽  
Wrf Model ◽  
Moist Convection ◽  
Lake Effect ◽  
Simulated Precipitation ◽  
Precipitation Estimates ◽  
Double Moment ◽  
Microphysical Processes

Abstract Simulations of moist convection at cloud-permitting grid spacings are sensitive to the parameterization of microphysical processes, posing a challenge for operational weather prediction. Here, the Weather Research and Forecasting (WRF) Model is used to examine the sensitivity of simulations of the Great Salt Lake–effect snowstorm of 27 October 2010 to the choice of microphysics parameterization (MP). It is found that the simulated precipitation from four MP schemes varies in areal coverage, amount, and position. The Thompson scheme (THOM) verifies best against radar-derived precipitation estimates and gauge observations. The Goddard, Morrison, and WRF double-moment 6-class microphysics schemes (WDM6) produce more precipitation than THOM, with WDM6 producing the largest overprediction relative to radar-derived precipitation estimates and gauge observations. Analyses of hydrometeor mass tendencies show that WDM6 creates more graupel, less snow, and more total precipitation than the other schemes. These results indicate that the rate of graupel and snow production can strongly influence the precipitation efficiency in simulations of lake-effect storms, but further work is needed to evaluate MP-scheme accuracy across a wider range of events, including the use of aircraft- and ground-based hydrometeor sampling to validate MP hydrometeor categorization.

Microphysics of Antarctic precipitation in climate models : recent advances and challenges

2020 ◽  
Author(s):  
Étienne Vignon ◽  
Josué Gehring ◽  
Simon P. Alexander ◽  
Georgia Sotiropoulou ◽  
Nikola Besic ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Wrf Model ◽  
Supercooled Liquid ◽  
Surface Mass ◽  
Current Assessment ◽  
Climate Model Simulations ◽  
Microphysical Processes ◽  
Antarctic Precipitation ◽  
The Antarctic

&lt;p align=&quot;justify&quot;&gt;&lt;span&gt;The current assessment of the Antarctic surface mass balance mostly relies on reanalysis products or climate model simulations. The ability of models to reproduce the precipitation field at the regional and continental scales not only depends on the simulation of the atmospheric dynamics over the Southern Ocean and of the advection of moisture towards the ice sheet, but also on the representation of the microphysical processes that govern the formation and growth of ice crystals and snowflakes. This presentation reviews recent studies to stress the importance and challenges of evaluating the precipitation microphysics over Antarctica in climate models. It also discusses how recent observational campaigns including ground-based remote-sensing instruments can help pinpoint key processes that should be represented in models. We then present tangible examples of evaluation and improvement of microphysical schemes in the Polar WRF model thanks to radar and lidar observations acquired near Dumont d&amp;#8217;Urville and Mawson stations on the Antarctic coast. Particular attention is devoted to three processes&amp;#160;: i) the sublimation of snowfall within the katabatic layer that considerably reduces the amount of precipitation that actually reaches the surface&amp;#160;; ii) the snowflake aggregation responsible for rapid depletion of crystals within clouds&amp;#160;; iii) the generation of supercooled liquid water in frontal clouds that leads to crystal/snowflake riming. Such studies, albeit preliminary, could pave the way for further evaluations of clouds and precipitation in climate models in different Antarctic contexts, especially in the cold and pristine atmosphere of the Plateau.&lt;/span&gt;&lt;/p&gt;

scholarly journals Evaluating the Snow Crystal Size Distribution and Density Assumptions within a Single-Moment Microphysics Scheme

2010 ◽  
Vol 138 (11) ◽  
pp. 4254-4267 ◽  
Author(s):  
Andrew L. Molthan ◽  
Walter A. Petersen ◽  
Stephen W. Nesbitt ◽  
David Hudak
Keyword(s):  
Size Distribution ◽  
Wrf Model ◽  
Terminal Velocity ◽  
Cold Season ◽  
Radiative Properties ◽  
Microphysics Scheme ◽  
Single Moment ◽  
Crystal Diameter ◽  
Forecast Models ◽  
Microphysical Processes

Abstract The Canadian CloudSat/Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Validation Project (C3VP) was a field campaign designed to obtain aircraft, surface, and radar observations of clouds and precipitation in support of improving the simulation of snowfall and cold season precipitation, their microphysical processes represented within forecast models, and radiative properties relevant to remotely sensed retrievals. During the campaign, a midlatitude cyclone tracked along the U.S.–Canadian border on 22 January 2007, producing an extensive area of snowfall. Observations of ice crystals from this event are used to evaluate the assumptions and physical relationships for the snow category within the Goddard six-class, single-moment microphysics scheme, as implemented within the Weather Research and Forecasting (WRF) model. The WRF model forecast generally reproduced the precipitation and cloud structures sampled by radars and aircraft, permitting a comparison between C3VP observations and model snowfall characteristics. Key snowfall assumptions in the Goddard scheme are an exponential size distribution with fixed intercept and effective bulk density, and the relationship between crystal diameter and terminal velocity. Fixed values for the size distribution intercept and density did not represent the vertical variability of naturally occurring populations of aggregates, and the current diameter and fall speed relationship underestimated terminal velocities for all sizes of crystals.

scholarly journals The Impact of Raindrop Collisional Processes on the Polarimetric Radar Variables

2014 ◽  
Vol 71 (8) ◽  
pp. 3052-3067 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Olivier P. Prat
Keyword(s):  
Electromagnetic Scattering ◽  
Vertical Profiles ◽  
Polarimetric Radar ◽  
Horizontal Polarization ◽  
One Dimensional ◽  
Microphysical Process ◽  
Warm Rain ◽  
Microphysical Processes ◽  
Differential Reflectivity ◽  
The Impact

Abstract The impact of the collisional warm-rain microphysical processes on the polarimetric radar variables is quantified using a coupled microphysics–electromagnetic scattering model. A one-dimensional bin-microphysical rain shaft model that resolves explicitly the evolution of the drop size distribution (DSD) under the influence of collisional coalescence and breakup, drop settling, and aerodynamic breakup is coupled with electromagnetic scattering calculations that simulate vertical profiles of the polarimetric radar variables: reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP. The polarimetric radar fingerprint of each individual microphysical process is quantified as a function of the shape of the initial DSD and for different values of nominal rainfall rate. Results indicate that individual microphysical processes (collisional processes, evaporation) display a distinctive signature and evolve within specific areas of ZH–ZDR and ZDR–KDP space. Furthermore, a comparison of the resulting simulated vertical profiles of the polarimetric variables with radar and disdrometer observations suggests that bin-microphysical parameterizations of drop breakup most frequently used are overly aggressive for the largest rainfall rates, resulting in very “tropical” DSDs heavily skewed toward smaller drops.

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