scholarly journals A Lagrangian Objective Analysis Technique for Assimilating In Situ Observations with Multiple-Radar-Derived Airflow

2007 ◽  
Vol 135 (7) ◽  
pp. 2417-2442 ◽  
Author(s):  
Conrad L. Ziegler ◽  
Michael S. Buban ◽  
Erik N. Rasmussen
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Potential Temperature ◽  
Cloud Base ◽  
Mixing Ratio ◽  
Lagrangian Analysis ◽  
Analysis Technique ◽  
Virtual Potential Temperature ◽  
Water Vapor Mixing Ratio

Abstract A new Lagrangian analysis technique is developed to assimilate in situ boundary layer measurements using multi-Doppler-derived wind fields, providing output fields of water vapor mixing ratio, potential temperature, and virtual potential temperature from which the lifting condensation level (LCL) and relative humidity (RH) fields are derived. The Lagrangian analysis employs a continuity principle to bidirectionally distribute observed values of conservative variables with the 3D, evolving boundary layer airflow, followed by temporal and spatial interpolation to an analysis grid. Cloud is inferred at any grid point whose height z > zLCL or equivalently where RH ≥ 100%. Lagrangian analysis of the cumulus field is placed in the context of gridded analyses of visible satellite imagery and photogrammetric cloud-base area analyses. Brief illustrative examples of boundary layer morphology derived with the Lagrangian analysis are presented based on data collected during the International H2O Project (IHOP): 1) a dryline on 22 May 2002; 2) a cold-frontal–dryline “triple point” intersection on 24 May 2002. The Lagrangian analysis preserves the sharp thermal gradients across the cold front and drylines and reveals the presence of undulations and plumes of water vapor mixing ratio and virtual potential temperature associated with deep penetrative updraft cells and convective roll circulations. Derived cloud fields are consistent with satellite-inferred cloud cover and cloud-base locations.

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

2019 ◽  
Vol 77 (3) ◽  
pp. 1081-1100 ◽  
Author(s):  
Neil P. Lareau
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

scholarly journals The “Triple Point” on 24 May 2002 during IHOP. Part II: Ground-Radar and In Situ Boundary Layer Analysis of Cumulus Development and Convection Initiation

2007 ◽  
Vol 135 (7) ◽  
pp. 2443-2472 ◽  
Author(s):  
Conrad L. Ziegler ◽  
Erik N. Rasmussen ◽  
Michael S. Buban ◽  
Yvette P. Richardson ◽  
L. Jay Miller ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Triple Point ◽  
Potential Temperature ◽  
Wind Fields ◽  
Analysis Technique ◽  
3D Fields ◽  
Water Vapor Mixing Ratio ◽  
Convection Initiation ◽  
Water Saturated

Abstract Cumulus formation and convection initiation are examined near a cold front–dryline “triple point” intersection on 24 May 2002 during the International H2O Project (IHOP). A new Lagrangian objective analysis technique assimilates in situ measurements using time-dependent Doppler-derived 3D wind fields, providing output 3D fields of water vapor mixing ratio, virtual potential temperature, and lifted condensation level (LCL) and water-saturated (i.e., cloud) volumes on a subdomain of the radar analysis grid. The radar and Lagrangian analyses reveal the presence of along-wind (i.e., longitudinal) and cross-wind (i.e., transverse) roll circulations in the boundary layer (BL). A remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft, vertical vorticity, and reflectivity cores for periods of up to 30 min or more while moving approximately with the local BL wind. Satellite cloud images and single-camera ground photogrammetry imply that clouds tend to develop either over or on the downwind edge of BL updrafts, with a tendency for clouds to elongate and dissipate in the downwind direction relative to cloud layer winds due to weakening updrafts and mixing with drier overlying air. The Lagrangian and radar wind analyses support a parcel continuity principle for cumulus formation, which requires that rising moist air parcels achieve their LCL before moving laterally out of the updraft. Cumuli form within penetrative updrafts in the elevated residual layer (ERL) overlying the moist BL east of the triple point, but remain capped by a convection inhibition (CIN)-bearing layer above the ERL. Dropsonde data suggest the existence of a convergence line about 80 km east of the triple point where deep lifting of BL moisture and locally reduced CIN together support convection initiation.

scholarly journals The Dryline on 22 May 2002 during IHOP: Ground-Radar and In Situ Data Analyses of the Dryline and Boundary Layer Evolution

2007 ◽  
Vol 135 (7) ◽  
pp. 2473-2505 ◽  
Author(s):  
Michael S. Buban ◽  
Conrad L. Ziegler ◽  
Erik N. Rasmussen ◽  
Yvette P. Richardson
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Doppler Radar ◽  
Potential Temperature ◽  
Vertical Motion ◽  
Temperature Fields ◽  
Lagrangian Analysis ◽  
Thermodynamic Structure ◽  
In Situ Data ◽  
Water Vapor Mixing Ratio

Abstract On the afternoon and evening of 22 May 2002, high-resolution observations of the boundary layer (BL) and a dryline were obtained in the eastern Oklahoma and Texas panhandles during the International H2O Project. Using overdetermined multiple-Doppler radar syntheses in concert with a Lagrangian analysis of water vapor and temperature fields, the 3D kinematic and thermodynamic structure of the dryline and surrounding BL have been analyzed over a nearly 2-h period. The dryline is resolved as a strong (2–4 g kg−1 km−1) gradient of water vapor mixing ratio that resides in a nearly north–south-oriented zone of convergence. Maintained through frontogenesis, the dryline is also located within a gradient of virtual potential temperature, which induces a persistent, solenoidally forced secondary circulation. Initially quasi-stationary, the dryline retrogrades to the west during early evening and displays complicated substructures including small wavelike perturbations that travel from south to north at nearly the speed of the mean BL flow. A second, minor dryline has similar characteristics to the first, but has weaker gradients and circulations. The BL adjacent to the dryline exhibits complicated structures, consisting of combinations of open cells, horizontal convective rolls, and transverse rolls. Strong convergence and vertical motion at the dryline act to lift moisture, and high-based cumulus clouds are observed in the analysis domain. Although the top of the analysis domain is below the lifted condensation level height, vertical extrapolation of the moisture fields generally agrees with cloud locations. Mesoscale vortices that move along the dryline induce a transient eastward dryline motion due to the eastward advection of dry air following misocyclone passage. Refractivity-based moisture and differential reflectivity analyses are used to help interpret the Lagrangian analyses.

scholarly journals A Simple Parameterization Coupling the Convective Daytime Boundary Layer and Fair-Weather Cumuli

2005 ◽  
Vol 62 (6) ◽  
pp. 1976-1988 ◽  
Author(s):  
Larry K. Berg ◽  
Roland B. Stull
Keyword(s):  
Boundary Layer ◽  
Cloud Cover ◽  
Potential Temperature ◽  
Joint Probability ◽  
Cloud Base ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Boundary Layer Cloud ◽  
Using Data ◽  
Water Vapor Mixing Ratio

Abstract A new parameterization for boundary layer cumulus clouds, called the cumulus potential (CuP) scheme, is introduced. This scheme uses joint probability density functions (JPDFs) of virtual potential temperature (θυ) and water-vapor mixing ratio (r), as well as the mean vertical profiles of θυ, to predict the amount and size distribution of boundary layer cloud cover. This model considers the diversity of air parcels over a heterogeneous surface, and recognizes that some parcels rise above their lifting condensation level to become cumulus, while other parcels might rise as noncloud updrafts. This model has several unique features: 1) cloud cover is determined from the boundary layer JPDF of θυ versus r, 2) clear and cloudy thermals are allowed to coexist at the same altitude, and 3) a range of cloud-base heights, cloud-top heights, and cloud thicknesses are predicted within any one cloud field, as observed. Using data from Boundary Layer Experiment 1996 and a model intercomparsion study using large eddy simulation (LES) based on Barbados Oceanographic and Meteorological Experiment (BOMEX), it is shown that the CuP model does a good job predicting cloud-base height and cloud-top height. The model also shows promise in predicting cloud cover, and is found to give better cloud-cover estimates than three other cumulus parameterizations: one based on relative humidity, a statistical scheme based on the saturation deficit, and a slab model.

scholarly journals Temperature profiling of the atmospheric boundary layer with rotational Raman lidar during the HD(CP)<sup>2</sup> Observational Prototype Experiment

2015 ◽  
Vol 15 (5) ◽  
pp. 2867-2881 ◽  
Author(s):  
E. Hammann ◽  
A. Behrendt ◽  
F. Le Mounier ◽  
V. Wulfmeyer
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Temperature Gradient ◽  
Atmospheric Boundary Layer ◽  
Average Power ◽  
Mixing Ratio ◽  
Raman Lidar ◽  
Backscatter Signal ◽  
Low Background ◽  
Water Vapor Mixing Ratio

Abstract. The temperature measurements of the rotational Raman lidar of the University of Hohenheim (UHOH RRL) during the High Definition of Clouds and Precipitation for advancing Climate Prediction (HD(CP)2) Observation Prototype Experiment (HOPE) in April and May 2013 are discussed. The lidar consists of a frequency-tripled Nd:YAG laser at 355 nm with 10 W average power at 50 Hz, a two-mirror scanner, a 40 cm receiving telescope, and a highly efficient polychromator with cascading interference filters for separating four signals: the elastic backscatter signal, two rotational Raman signals with different temperature dependence, and the vibrational Raman signal of water vapor. The main measurement variable of the UHOH RRL is temperature. For the HOPE campaign, the lidar receiver was optimized for high and low background levels, with a novel switch for the passband of the second rotational Raman channel. The instrument delivers atmospheric profiles of water vapor mixing ratio as well as particle backscatter coefficient and particle extinction coefficient as further products. As examples for the measurement performance, measurements of the temperature gradient and water vapor mixing ratio revealing the development of the atmospheric boundary layer within 25 h are presented. As expected from simulations, a reduction of the measurement uncertainty of 70% during nighttime was achieved with the new low-background setting. A two-mirror scanner allows for measurements in different directions. When pointing the scanner to low elevation, measurements close to the ground become possible which are otherwise impossible due to the non-total overlap of laser beam and receiving telescope field of view in the near range. An example of a low-level temperature measurement is presented which resolves the temperature gradient at the top of the stable nighttime boundary layer 100 m above the ground.

scholarly journals Intercomparison of in situ water vapor balloon-borne measurements from Pico-SDLA H<sub>2</sub>O and FLASH-B in the tropical UTLS

2015 ◽  
Vol 8 (12) ◽  
pp. 13693-13727
Author(s):  
M. Ghysels ◽  
E. D. Riviere ◽  
S. Khaykin ◽  
C. Stoeffler ◽  
N. Amarouche ◽  
...  
Keyword(s):  
Water Vapor ◽  
Low Cost ◽  
Deep Convection ◽  
Mixing Ratio ◽  
Stratospheric Water Vapor ◽  
In Situ Techniques ◽  
Scientific Project ◽  
Water Vapor Mixing Ratio ◽  
The Impact

Abstract. In this paper we compare water vapor mixing ratio measurements from two quasi-parallel flights of the Pico-SDLA H2O and FLASH-B hygrometers. The measurements were made on 10 February 2013 and 13 March 2012, respectively, in the tropics near Bauru, Sao Paulo St., Brazil during an intense convective period. Both flights were performed as part of a French scientific project, TRO-Pico, to study the impact of the deep-convection overshoot on the water budget. Only a few instruments that permit the frequent sounding of stratospheric water vapor can be flown within a small volume weather balloons. Technical difficulties preclude the accurate measurement of stratospheric water vapor with conventional in situ techniques. The instruments described here are simple and lightweight, which permits their low-cost deployment by non-specialists aboard a small weather balloon. We obtain mixing ratio retrievals which agree above the cold-point tropopause to within 1.9 and 0.5 % for the first and second flights, respectively. This level of agreement for measured stratospheric water mixing ratio is among the best ever reported in the literature. Because both instruments show similar profiles within their combined uncertainties, we conclude that the Pico-SDLA H2O and FLASH-B datasets are mutually consistent.

scholarly journals An Automated Detection Methodology for Dry Well-Mixed Layers

2019 ◽  
Vol 36 (5) ◽  
pp. 761-779
Author(s):  
Stephen D. Nicholls ◽  
Karen I. Mohr
Keyword(s):  
Water Vapor ◽  
Vertical Profile ◽  
Input Data ◽  
Profile Analysis ◽  
Potential Temperature ◽  
Data File ◽  
Mixing Ratio ◽  
Land Surfaces ◽  
Water Vapor Mixing Ratio ◽  
Mixed Layers

AbstractThe intense surface heating over arid land surfaces produces dry well-mixed layers (WML) via dry convection. These layers are characterized by nearly constant potential temperature and low, nearly constant water vapor mixing ratio. To further the study of dry WMLs, we created a detection methodology and supporting software to automate the identification and characterization of dry WMLs from multiple data sources including rawinsondes, remote sensing platforms, and model products. The software is a modular code written in Python, an open-source language. Radiosondes from a network of synoptic stations in North Africa were used to develop and test the WML detection process. The detection involves an iterative decision tree that ingests a vertical profile from an input data file, performs a quality check for sufficient data density, and then searches upward through the column for successive points where the simultaneous changes in water vapor mixing ratio and potential temperature are less than the specified maxima. If points in the vertical profile meet the dry WML identification criteria, statistics are generated detailing the characteristics of each layer in the profile. At the end of the vertical profile analysis, there is an option to plot analyzed profiles in a variety of file formats. Initial results show that the detection methodology can be successfully applied across a wide variety of input data and North African environments and for all seasons. It is sensitive enough to identify dry WMLs from other types of isentropic phenomena such as subsidence layers and distinguish the current day’s dry WML from previous days.

Demonstration Measurements of Water Vapor, Cirrus Clouds, and Carbon Dioxide Using a High-Performance Raman Lidar

2007 ◽  
Vol 24 (8) ◽  
pp. 1377-1388 ◽  
Author(s):  
David N. Whiteman ◽  
Kurt Rush ◽  
Igor Veselovskii ◽  
Martin Cadirola ◽  
Joseph Comer ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Water Vapor ◽  
High Performance ◽  
Cirrus Clouds ◽  
Mixing Ratio ◽  
Raman Lidar ◽  
Cloud Optical Depth ◽  
Temporal And Spatial ◽  
Water Vapor Mixing Ratio

Abstract Profile measurements of atmospheric water vapor, cirrus clouds, and carbon dioxide using the Raman Airborne Spectroscopic lidar (RASL) during ground-based, upward-looking tests are presented here. These measurements improve upon any previously demonstrated using Raman lidar. Daytime boundary layer profiling of water vapor mixing ratio up to an altitude of approximately 4 km under moist, midsummer conditions is performed with less than 5% random error using temporal and spatial resolution of 2 min and 60–210 m, respectively. Daytime cirrus cloud optical depth and extinction-to-backscatter ratio measurements are made using a 1-min average. The potential to simultaneously profile carbon dioxide and water vapor mixing ratio through the boundary layer and extending into the free troposphere during the nighttime is also demonstrated.

scholarly journals Comparison of Fast In situ Stratospheric Hygrometer (FISH) measurements of water vapor in the upper troposphere and lower stratosphere (UTLS) with ECMWF (re)analysis data

2014 ◽  
Vol 14 (19) ◽  
pp. 10803-10822 ◽  
Author(s):  
A. Kunz ◽  
N. Spelten ◽  
P. Konopka ◽  
R. Müller ◽  
R. M. Forbes ◽  
...  
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Analysis Data ◽  
Large Set ◽  
Mixing Ratio ◽  
Perfect Agreement ◽  
Upper Troposphere ◽  
Time Periods ◽  
Water Vapor Mixing Ratio

Abstract. An evaluation of water vapor in the upper troposphere and lower stratosphere (UTLS) of the ERA-Interim, the global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), is presented. Water vapor measurements are derived from the Fast In situ Stratospheric Hygrometer (FISH) during a large set of airborne measurement campaigns from 2001 to 2011 in the tropics, midlatitudes and polar regions, covering isentropic layers from 300 to 400K (5–18km). The comparison shows around 87% of the reanalysis data are within a factor of 2 of the FISH water vapor measurements and around 30% have a nearly perfect agreement with an over- and underestimation lower than 10%. Nevertheless, strong over- and underestimations can occur both in the UT and LS, in particularly in the extratropical LS and in the tropical UT, where severe over- and underestimations up to 10 times can occur. The analysis data from the evolving ECMWF operational system is also evaluated, and the FISH measurements are divided into time periods representing different cycles of the Integrated Forecast System (IFS). The agreement with FISH improves over the time, in particular when comparing water vapor fields for time periods before 2004 and after 2010. It appears that influences of tropical tropospheric and extratropical UTLS processes, e.g., convective and quasi-isentropic exchange processes, are particularly challenging for the simulation of the UTLS water vapor distribution. Both the reanalysis and operational analysis data show the tendency of an overestimation of low water vapor mixing ratio (&amp;lessapprox;10ppmv) in the LS and underestimation of high water vapor mixing ratio (&amp;gtrapprox;300ppmv) in the UT.

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