scholarly journals Implementation of a 2D Wavelet Method to Probe Mixed Layer Height Using Lidar Observations

2019 ◽  
Vol 16 (14) ◽  
pp. 2516 ◽  
Author(s):  
Ning Zhang ◽  
Fuyan Yang ◽  
Yan Chen
Keyword(s):  
Mixed Layer ◽  
Early Morning ◽  
New Method ◽  
Data Quality Control ◽  
Wavelet Method ◽  
Wavelet Filters ◽  
Radiosonde Observation ◽  
Variation Characteristics ◽  
Mixed Layer Height ◽  
Lidar Observations

A new method was developed to estimate mixed layer (ML) height with light detection and ranging (lidar) observations using a 2Dimensional (2D) wavelet method, which can consider the diurnal variation characteristics of ML height. Ideal signals and real lidar observations in Shanghai, China were used to evaluate the new method. The results showed that the new method is insensitive to the type of wavelet filters. The estimated ML heights obtained by the 2D wavelet method agreed well with both of the previous methods developed for the ML height probing using lidar, including the gradient method, the 1D-wavelet method, the standard deviation method, and the conventional radiosonde method. The primary differences among the results obtained via the different lidar methods occurred in the early morning or later afternoon; when the ML is well mixed, very small differences were observed among the different lidar methods. The new method showed better determination skills than other methods when compared to the radiosonde observation results. It also performed well when there were missing profiles or observation errors and it made the new method suitable for operations where data quality control may be missed.

scholarly journals Estimation of urban mixed layer height in Zanjan using LIDAR observations and numerical modeling

2008 ◽  
Vol 117 (6) ◽  
pp. 925-934 ◽  
Author(s):  
A. A. Bidokhti ◽  
M. Khoshsima ◽  
S. Sabetghadam ◽  
H. M. Khalesifard
Keyword(s):  
Numerical Modeling ◽  
Mixed Layer ◽  
Layer Height ◽  
Mixed Layer Height ◽  
Lidar Observations

scholarly journals Assessment of mixed-layer height estimation from single-wavelength ceilometer profiles

2017 ◽  
Vol 10 (10) ◽  
pp. 3963-3983 ◽  
Author(s):  
Travis N. Knepp ◽  
James J. Szykman ◽  
Russell Long ◽  
Rachelle M. Duvall ◽  
Jonathan Krug ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Data Collection ◽  
Mixed Layer ◽  
A Priori ◽  
Processing Algorithm ◽  
Height Measurement ◽  
Layer Height ◽  
Network Operation ◽  
Mixed Layer Height ◽  
The Impact

Abstract. Differing boundary/mixed-layer height measurement methods were assessed in moderately polluted and clean environments, with a focus on the Vaisala CL51 ceilometer. This intercomparison was performed as part of ongoing measurements at the Chemistry And Physics of the Atmospheric Boundary Layer Experiment (CAPABLE) site in Hampton, Virginia and during the 2014 Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign that took place in and around Denver, Colorado. We analyzed CL51 data that were collected via two different methods (BLView software, which applied correction factors, and simple terminal emulation logging) to determine the impact of data collection methodology. Further, we evaluated the STRucture of the ATmosphere (STRAT) algorithm as an open-source alternative to BLView (note that the current work presents an evaluation of the BLView and STRAT algorithms and does not intend to act as a validation of either). Filtering criteria were defined according to the change in mixed-layer height (MLH) distributions for each instrument and algorithm and were applied throughout the analysis to remove high-frequency fluctuations from the MLH retrievals. Of primary interest was determining how the different data-collection methodologies and algorithms compare to each other and to radiosonde-derived boundary-layer heights when deployed as part of a larger instrument network. We determined that data-collection methodology is not as important as the processing algorithm and that much of the algorithm differences might be driven by impacts of local meteorology and precipitation events that pose algorithm difficulties. The results of this study show that a common processing algorithm is necessary for light detection and ranging (lidar)-based MLH intercomparisons and ceilometer-network operation, and that sonde-derived boundary layer heights are higher (10–15 % at midday) than lidar-derived mixed-layer heights. We show that averaging the retrieved MLH to 1 h resolution (an appropriate timescale for a priori data model initialization) significantly improved the correlation between differing instruments and differing algorithms.

scholarly journals Observational estimates of detrainment and entrainment in non-precipitating shallow cumulus

2016 ◽  
Vol 16 (1) ◽  
pp. 21-33 ◽  
Author(s):  
M. S. Norgren ◽  
J. D. Small ◽  
H. H. Jonsson ◽  
P. Y. Chuang
Keyword(s):  
Mixed Layer ◽  
Vertical Transport ◽  
New Method ◽  
Atmospheric Composition ◽  
Cumulus Clouds ◽  
Neutral Buoyancy ◽  
Mass Fractions ◽  
Static Energy ◽  
Almost All ◽  
Entrained Air

Abstract. Vertical transport associated with cumulus clouds is important to the redistribution of gases, particles, and energy, with subsequent consequences for many aspects of the climate system. Previous studies have suggested that detrainment from clouds can be comparable to the updraft mass flux, and thus represents an important contribution to vertical transport. In this study, we describe a new method to deduce the amounts of gross detrainment and entrainment experienced by non-precipitating cumulus clouds using aircraft observations. The method utilizes equations for three conserved variables: cloud mass, total water, and moist static energy. Optimizing these three equations leads to estimates of the mass fractions of adiabatic mixed-layer air, entrained air and detrained air that the sampled cloud has experienced. The method is applied to six flights of the CIRPAS Twin Otter during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) which took place in the Houston, Texas region during the summer of 2006 during which 176 small, non-precipitating cumuli were sampled. Using our novel method, we find that, on average, these clouds were comprised of 30 to 70 % mixed-layer air, with entrained air comprising most of the remainder. The mass fraction of detrained air was usually very small, less than 2 %, although values larger than 10 % were found in 15 % of clouds. Entrained and detrained air mass fractions both increased with altitude, consistent with some previous observational studies. The largest detrainment events were almost all associated with air that was at their level of neutral buoyancy, which has been hypothesized in previous modeling studies. This new method could be readily used with data from other previous aircraft campaigns to expand our understanding of detrainment for a variety of cloud systems.

Dynamics of Mixed Layer in a Nonuniformly Stratified Fluid Heated from Below

1980 ◽  
Vol 102 (2) ◽  
pp. 134-141 ◽  
Author(s):  
M. Behnia ◽  
R. Viskanta
Keyword(s):  
Natural Convection ◽  
Mixed Layer ◽  
Laboratory Experiments ◽  
Turbulence Models ◽  
Finite Depth ◽  
Stratified Fluid ◽  
Stable Region ◽  
Turbulent Natural Convection ◽  
Mixed Layer Height ◽  
Unsteady Natural Convection

Unsteady natural convection in a nonuniformly stratified, finite depth layer of water heated from below has been studied. Laboratory experiments were performed using the Mach-Zehnder interferometer as a diagnostic tool for measuring temperature. A shadowgraph technique was used for flow visualization. A simple thermal and a more detailed two-differential equation k–ε turbulence models are used to predict the dynamics of mixed layer which develops when the thermally stratified fluid is heated from below. The thermal model predictions for the mixed layer height agreed to within 5 percent and the mixed layer temperature to within 15 percent of the experimental data obtained in controlled laboratory experiments. Even better agreement between data and predictions were obtained with the k–ε turbulence model. The entrainment processes at the interface between the mixed layer and the stable region as well as turbulence in the layer must be better understood for more realistic modeling of turbulent natural convection in nonuniformly stratified fluids.

scholarly journals The Evaluation of a New Method to Detect Mixing Layer Heights Using Lidar Observations

2015 ◽  
Vol 32 (11) ◽  
pp. 2041-2051 ◽  
Author(s):  
Micheal Hicks ◽  
Ricardo Sakai ◽  
Everette Joseph
Keyword(s):  
Hybrid Method ◽  
Detection Method ◽  
Error Function ◽  
Mixing Layer ◽  
New Method ◽  
Mixing Height ◽  
Critical Components ◽  
Sky Conditions ◽  
Aerosol Backscatter ◽  
Lidar Observations

AbstractA new automatic mixing layer height detection method for lidar observations of aerosol backscatter profiles is presented and evaluated for robustness. The new detection method incorporates the strengths of Steyn et al.’s error function–ideal profile (ERF) method and Davis et al.’s wavelet covariance transform (WCT) method. These two methods are critical components of the new method, and their robustness is also evaluated and then contrasted to the new method. The new method is applied to aerosol backscatter observations in two ways: 1) by looking for the most realistic mixing height throughout the entire profile and 2) by searching for mixing height below significant elevated obscurations (e.g., clouds or aerosol layers). The first approach is referred to as the hybrid method and the second as the hybrid-lowest method. Coincident radiosounding observations of mixing heights are used to independently reference the lidar-based estimates.There were 4030 cases examined over a 5-yr period for mixing heights. The efficacy of the lidar-based methods was determined based on diurnal, seasonal, stability, and sky obscuration conditions. Of these conditions, the hybrid method performed best for unstable and cloudy situations. It determined mixing heights reliably (less than ±0.30-km bias) for close to 70% of those cases. The hybrid-lowest method performed best in stable and clear-sky conditions; it determined mixing heights reliably for over 70% of those cases. The WCT method performed the best overall.

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