Large Lapse Rates Research Articles

Interpretable Deep Learning for Spatial Analysis of Severe Hailstorms

AbstractDeep learning models, such as convolutional neural networks, utilize multiple specialized layers to encode spatial patterns at different scales. In this study, deep learning models are compared with standard machine learning approaches on the task of predicting the probability of severe hail based on upper-air dynamic and thermodynamic fields from a convection-allowing numerical weather prediction model. The data for this study come from patches surrounding storms identified in NCAR convection-allowing ensemble runs from 3 May to 3 June 2016. The machine learning models are trained to predict whether the simulated surface hail size from the Thompson hail size diagnostic exceeds 25 mm over the hour following storm detection. A convolutional neural network is compared with logistic regressions using input variables derived from either the spatial means of each field or principal component analysis. The convolutional neural network statistically significantly outperforms all other methods in terms of Brier skill score and area under the receiver operator characteristic curve. Interpretation of the convolutional neural network through feature importance and feature optimization reveals that the network synthesized information about the environment and storm morphology that is consistent with our understanding of hail growth, including large lapse rates and a wind shear profile that favors wide updrafts. Different neurons in the network also record different storm modes, and the magnitude of the output of those neurons is used to analyze the spatiotemporal distributions of different storm modes in the NCAR ensemble.

Comparing adaptive procedures for estimating the psychometric function for an auditory gap detection task

A subject's sensitivity to a stimulus variation can be studied by estimating the psychometric function. Generally speaking, three parameters of the psychometric function are of interest: the performance threshold, the slope of the function, and the rate at which attention lapses occur. In the present study, three psychophysical procedures were used to estimate the three-parameter psychometric function for an auditory gap detection task. These were an up-down staircase (up-down) procedure, an entropy-based Bayesian (entropy) procedure, and an updated maximum-likelihood (UML) procedure. Data collected from four young, normal-hearing listeners showed that while all three procedures provided similar estimates of the threshold parameter, the up-down procedure performed slightly better in estimating the slope and lapse rate for 200 trials of data collection. When the lapse rate was increased by mixing in random responses for the three adaptive procedures, the larger lapse rate was especially detrimental to the efficiency of the up-down procedure, and the UML procedure provided better estimates of the threshold and slope than did the other two procedures.

Investigation of Upper-Air Conditions Occurring with Warm Season Severe Wind Events in Utah

Abstract Analyses of proximity soundings and upper-air fields for 37–51 Utah severe wind cases (WIND), reported in the months of May–September and occurring within 3 h after upper-air observation time, are presented. In addition, a comparison of sample mean values between the WIND cases and a climatological sample (CLIM) is made using a standard t test to determine which variables are significantly different between the two samples. This study seeks to determine if the synoptic-scale-derived fields play a significant role in producing severe wind for a region in which subsynoptic effects, attributed to uneven terrain, are important. The WIND sample environment had the following important differences when compared to CLIM: more convergent wind in the lower troposphere (700-mb moisture and wind convergence), greater moisture at 500 mb (dewpoint, mixing ratio), greater positive vorticity advection (500 mb) and differential vorticity advection (700–500 mb), a larger lapse rate based on various stability indic...

Very Large Potential Temperature Lapse Rates and Low Turbulence Levels during Spring Thaw on the Prairies

Abstract Observations show that two phenomena that are generally considered mutually exclusive occur both night and day during spring thaw over flat cultivated prairies: extremely large potential temperature lapse rates and low levels of atmospheric turbulence. Magnitudes of the large lapse rates routinely exceeded 20°C (100 m)−1, whereas levels of turbulence during night and day were at values usually associated with moderately stable and near neutral conditions, respectively. Coexistence of these phenomena occurs during the time of year when a significantly large portion of the prairie is characterized by water and/or ice while the remainder comprises bare soil surfaces. Whereas freezing water is a sensible heat source during the night and melting ice a heat sink during the day, the bare soil acts in a reverse manner being a heat sink during the night and a source during the day. Air moving over the prairie surface is, therefore, subject to, both day and night, an alternating succession of warm and cool...

Zur vertikalen verteilung der luft- und pflanzentemperatur in einem buchenhochwald, besonders im kronenraum

Measurements of the temperature of the air and the plants were made inside and above a 31-m high beech forest near Göttingen up to 43 m altitude as well as of the soil temperature using ventilated thermometers and IR-thermometers, as appropriate. The temperature of the canopy was also calculated from the upward longwave radiation after allowing for the reflection of the downward radiation. Some results for cloudless conditions are presented. The profile of the air temperature is governed by the temperature of all surfaces: soil, trees and the upper side of the canopy. The soil surface is the main agent in the defoliated forest causing large lapse rates in daytime and strong inversions during the night. The air in the stand is often some degrees cooler than the tree surfaces in the daytime. The canopy of the foliated forest shows a large variability in its temperature, but it is an important heating surface in daytime and a cooling surface at night-time for the air above and below it. The soil surface and also the trunks and twigs are usually cooler than the air inside the stand except after the invasion of cold air. Inside the stand there is generally, therefore, an inversion, which is stronger the cooler the soil surface is. The turbulent downward flux is the main heat supply for trunks and soil and is more important than the small net radiation inside the forest. During warm nights and weak winds a strong inversion was often observed between the soil surface and 43 m. However, there are unstable lapse rates in the upper half of the canopy (25–31 m) during cold nights with weak winds. This surely facilitates the vertical air exchange on frosty nights in spring and in the fall and prevents the forest from being a significant source of katabatic cold air currents.

Classification of mesoscale vortices in polar airstreams and the influence of the large-scale environment on their evolutions

Satellite imagery was used to detect and study 133 mesoscale cloud vortices which occurred in the northeastern Atlantic Ocean and adjacent seas between 1 December 1981 and 5 January 1982. Only vortices occurring in cold air, separate from synoptic-scale frontal cloud bands, were considered. The complete history of the evolution of each cloud vortex was recorded in terms of its location, size, cloud pattern, and cloud type (shallow or deep; stratiform or convective). Once all vortices were documented, conventional meteorological data and analyses were consulted. One objective of the study was to determine whether satellite imagery could be used to estimate the central pressure of the cyclones accompanying the mesoscale vortices. Other objectives were to determine if there were significant differences in (1) the mesoscale cloud structure or (2) the large-scale environment of vortices which remained insignificant versus those that developed into polar lows. Results indicate that the deficit pressure of the polar vortex could be estimated from satellite imagery and that there were recognizable differences between developing and non-developing vortices. Only a few cloud configurations accompanied polar lows, whereas the occurrence of certain other configurations at early stages in the vortex existence indicated that these vortices would remain insignificant. The synoptic-scale environment appeared to play a considerable role in determining which incipient vortices continued to develop. Moderate baroclinicity (horizontal temperature gradients and vertical wind shear), relatively weak winds, large lapse rates, and favorable vorticity advections accompanied developing polar lows. Non-developing vortices had unfavorable vorticity advections. Of these, some vortices were able to grow initially to moderate disturbances which remained steady thereafter. The apparent difference between these and insignificant vortices was that the steady vortices were more baroclinic and had steeper lapse rates. DOI: 10.1111/j.1600-0870.1985.tb00276.x