scholarly journals Direct Assimilation of Radar Reflectivity without Tangent Linear and Adjoint of the Nonlinear Observation Operator in the GSI-Based EnVar System: Methodology and Experiment with the 8 May 2003 Oklahoma City Tornadic Supercell

2017 ◽  
Vol 145 (4) ◽  
pp. 1447-1471 ◽  
Author(s):  
Yongming Wang ◽  
Xuguang Wang
Keyword(s):  
Radar Reflectivity ◽  
Oklahoma City ◽  
New Method ◽  
Cold Pool ◽  
Mixing Ratio ◽  
State Variables ◽  
Low Level ◽  
Mixing Ratios ◽  
Convective Scale ◽  
Nonlinear Observation

Abstract A GSI-based EnVar data assimilation system is extended to directly assimilate radar reflectivity to initialize convective-scale forecasts. When hydrometeor mixing ratios are used as state variables (method mixing ratio), large differences of the cost function gradients with respect to the small hydrometeor mixing ratios and wind prevent efficient convergence. Using logarithmic mixing ratios as state variables (method logarithm) fixes this problem, but generates spuriously large hydrometeor increments partly due to the transform to and from the logarithmic space. The tangent linear of the reflectivity operators further contributes to spuriously small and large hydrometeor increments in method mixing ratio and method logarithm, respectively. A new method is proposed by directly adding the reflectivity as a state variable (method dBZ). Without the tangent linear and adjoint of the nonlinear operator, the new method therefore avoids the aforementioned problems. The newly proposed method is examined on the analysis and prediction of the 8 May 2003 Oklahoma City tornadic supercell storm. Both the probabilistic forecast of strong low-level vorticity and maintenance of strong updraft and vorticity in method dBZ are more consistent with reality than in method logarithm and method mixing ratio. Detailed diagnostics suggest that a more realistic cold pool due to the better analyzed hydrometeors in method dBZ than in other methods leads to constructive interaction between the surface gust front and the updraft aloft associated with the midlevel mesocyclone. Similar low-level vorticity forecast and maintenance of the storm are produced by the WSM6 and Thompson microphysics schemes in method dBZ. The Thompson scheme matches the reflectivity distribution with the observations better for all lead times, but shows more southeastward track bias compared to the WSM6 scheme.

scholarly journals On the Creation and Evolution of Small-Scale Low-Level Vorticity Anomalies during Tropical Cyclogenesis

2019 ◽  
Vol 76 (8) ◽  
pp. 2335-2355 ◽  
Author(s):  
Warren P. Smith ◽  
Melville E. Nicholls
Keyword(s):  
Environmental Parameters ◽  
Cold Pool ◽  
Tropical Cyclogenesis ◽  
Small Scale ◽  
Low Level ◽  
Cold Pools ◽  
Convective Scale ◽  
Vortical Hot Towers ◽  
Formation And Evolution ◽  
Vortex Merger

Abstract Recent numerical modeling and observational studies indicate the importance of vortical hot towers (VHTs) in the transformation of a tropical disturbance to a tropical depression. It has recently been recognized that convective-scale downdraft outflows that form within VHTs also preferentially develop positive vertical vorticity around their edges, which is considerably larger in magnitude than ambient values. During a numerical simulation of tropical cyclogenesis it is found that particularly strong low-level convectively induced vorticity anomalies (LCVAs) occasionally form as convection acts on the enhanced vorticity at the edges of cold pools. These features cycle about the larger-scale circulation and are associated with a coincident pressure depression and low-level wind intensification. The LCVAs studied are considerably deeper than the vorticity produced at the edges of VHT cold pool outflows, and their evolution is associated with persistent convection and vortex merger events that act to sustain them. Herein, we highlight the formation and evolution of two representative LCVAs and discuss the environmental parameters that eventually become favorable for one LCVA to reach the center of a larger-scale circulation as tropical cyclogenesis occurs.

scholarly journals Vertical Moistening by AMMA Mesoscale Convective Systems

2011 ◽  
Vol 28 (5) ◽  
pp. 617-639 ◽  
Author(s):  
G. Scialom ◽  
Y. Lemaître
Keyword(s):  
Energy Transport ◽  
Low Cost ◽  
Radar Data ◽  
Radar Reflectivity ◽  
Mixing Ratio ◽  
Convective Systems ◽  
Wind Analysis ◽  
Empirical Relations ◽  
Convective Scale ◽  
Mesoscale Convective

Abstract The apparent heat source Q1 and the apparent moisture sink Q2 are crucial parameters for precipitating systems studies because they allow for the evaluation of their contribution in water and energy transport and infer some of the mechanisms that are responsible for their evolution along their lifetime. In this paper, a new approach is proposed to estimate Q2 budgets from radar observations within precipitating areas at the scale of the measurements, that is, either convective scale or mesoscale, depending on the selected retrieval zone. This approach relies upon a new analysis of the radar reflectivity based on the concept of the traditional velocity–azimuth display (VAD) analysis. From the following five steps, Q2 is deduced from velocity and reflectivity fields: (i) mixing ratio retrieval using empirical relations, (ii) radial wind analysis using the VAD analysis, (iii) radar reflectivity analysis using a new analysis called reflectivity–azimuth display (RAD), (iv) retrieval of mixing ratio derivatives, and (v) Q2 retrieval. The originality and the main interest of the present approach with respect to previous studies rely on the fact it uses radar data alone and is based on a relatively low-cost analysis, allowing future systematic application on large datasets. In the present paper, this analysis is described and its robustness is evaluated and illustrated on three cases observed during the African Monsoon Multidisciplinary Analyses (AMMA) special observing period (SOP) field experiment (15 June–15 September) by means of the Recherche sur les Orages et Nuages par un Système Associé de Radars Doppler (RONSARD) radar. Results are analyzed in terms of the convective or stratiform character of observed precipitation.

scholarly journals Friagem Event in Central Amazon and its Influence on Micrometeorological Variables and Atmospheric Chemistry

2020 ◽  
Author(s):  
Guilherme F. Camarinha-Neto ◽  
Julia C. P. Cohen ◽  
Cléo Q. Dias-Júnior ◽  
Matthias Sörgel ◽  
José Henrique Cattanio ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Temperature Drop ◽  
Atmospheric Modeling ◽  
Amazon Region ◽  
Cold Pool ◽  
Large Temperature ◽  
Mixing Ratio ◽  
Air Masses ◽  
Central Amazon ◽  
Mixing Ratios

Abstract. In the period between July 9th and 11th, 2014 a Friagem event reached the central Amazon region causing significant changes in microclimate and atmospheric chemistry. On July 11th, the southwest flow related to the Friagem converged with the easterly winds in the central Amazon region. The interaction between these two distinct air masses formed a convection band, which intensified over the Manaus region and the Amazon Tall Tower Observatory (ATTO) site. The satellite images show the evolution of convective activity on July 11th, which lead to 21 mm of precipitation in the ATTO site. Moreover, the arrival of the Friagem caused a sudden drop in temperature and a predominance of southerly winds, which could be seen in Porto Velho between July 7th and 8th and in Manaus and ATTO site from July 9th to 11th. The results of ERA reanalysis and Brazilian developments on the Regional Atmospheric Modeling System (BRAMS) simulations show that this Friagem event coming from the southwest, carries a mass of air with higher O3 and NO2 mixing ratios and lower CO mixing ratio compared to the air masses present at the central Amazon. At lake Balbina the Friagem intensifies the local circulations, such as the breeze phenomena. At the Manaus region and ATTO site, the main effects of the Friagem event are: a decrease in the incoming solar radiation (due to intense cloud formation), a large temperature drop and a distinct change in surface O3 and CO2 mixing ratios. As the cold air of the Friagem was just in the lower 500 m the most probable cause of this change is that a cold pool above the forest prevented vertical mixing causing accumulation of CO2 from respiration and very low O3 mixing ratio due to photochemistry reduction and limited mixing within the boundary layer.

scholarly journals Influence of Low-Level Thermodynamic Structure on the Downdraft Properties of Simulated Supercells

2012 ◽  
Vol 140 (8) ◽  
pp. 2575-2589 ◽  
Author(s):  
Jason Naylor ◽  
Mark A. Askelson ◽  
Matthew S. Gilmore
Keyword(s):  
Potential Temperature ◽  
Weather Research And Forecasting ◽  
Cold Pool ◽  
Forecasting Model ◽  
Mixing Ratio ◽  
Near Surface ◽  
Thermodynamic Structure ◽  
Low Level ◽  
Capping Inversion

Abstract Idealized simulations using the Weather Research and Forecasting Model (WRF) were performed to examine the role of capping inversions on the near-surface thermodynamic structure of outflow from simulated supercells. Two simulations were performed: one with the traditional noncapped Weisman and Klemp (WK) analytic sounding and the second with a WK sounding modified to contain a capping inversion. Both sounding environments favor splitting storms and a right-moving supercell by 90 min into the simulation. These two supercell simulations evolve in a qualitatively similar fashion, with both storms exhibiting large, quasi-steady updrafts, hook-shaped appendages in the precipitation mixing ratio field, and prominent localized downdrafts. Results show that the supercell simulated in the capped environment has a surface cold pool with larger values of pseudoequivalent potential temperature (θep) than the cold pool of the supercell produced in the noncapped simulation. Parcels in the surface cold pool of the supercell produced in the capped sounding simulation have a lower origin height than those in the surface cold pool of the supercell produced in the noncapped simulation for all times. Although θep values in the surface cold pool are primarily associated with the origin height of downdraft parcels and the environmental θep at that level, it is shown that nonconservation of θep primarily associated with hydrometeor melting can decrease θep values of downdraft parcels as they descend by several degrees.

scholarly journals On the Squall Lines Preceding Landfalling Tropical Cyclones in China

2012 ◽  
Vol 140 (2) ◽  
pp. 445-470 ◽  
Author(s):  
Zhiyong Meng ◽  
Yunji Zhang
Keyword(s):  
Tropical Cyclones ◽  
Radar Reflectivity ◽  
Vertical Shear ◽  
Cold Pool ◽  
Low Level ◽  
Squall Lines ◽  
Suboptimal Condition ◽  
Moist Environment ◽  
Conditional Instability ◽  
Landfalling Tropical Cyclones

Based on a 3-yr (2007–09) mosaic of radar reflectivity and conventional surface and synoptic radiosonde observations, the general features of squall lines preceding landfalling tropical cyclones (TCs) (pre-TC) in China are examined and compared with their midlatitude and subtropical counterparts. The results show that about 40% of landfalling TCs are associated with pre-TC squall lines with high-occurring frequency in August and from late afternoon to midnight. Most pre-TC squall lines form in a broken-line mode with a trailing-stratiform organization. On average, they occur about 600 km from the TC center in the front-right quadrant with a maximum length of 220 km, a maximum radar reflectivity of 57–62 dBZ, a life span of 4 h, and a moving speed of 12.5 m s−1. Pre-TC squall lines are generally shorter in lifetime and length than typical midlatitude squall lines. Pre-TC squall lines tend to form in the transition area between the parent TC and subtropical high in a moist environment and with a weaker cold pool than their midlatitude counterparts. The environmental 0–3-km vertical shear is around 10 m s−1 and generally normal to the orientation of the squall lines. This weak shear makes pre-TC squall lines in a suboptimal condition according to the Rottuno–Klemp–Weisman (RKW) theory. Convection is likely initiated by low-level mesoscale frontogenesis, convergence, and/or confluence instead of synoptic-scale forcing. The parent TC may contribute to (i) the development of convection by enhancing conditional instability and low-level moisture supply, and (ii) the linear organization of discrete convection through the interaction between the TC and the neighboring environmental system.

scholarly journals The friagem event in the central Amazon and its influence on micrometeorological variables and atmospheric chemistry

2021 ◽  
Vol 21 (1) ◽  
pp. 339-356
Author(s):  
Guilherme F. Camarinha-Neto ◽  
Julia C. P. Cohen ◽  
Cléo Q. Dias-Júnior ◽  
Matthias Sörgel ◽  
José Henrique Cattanio ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Temperature Drop ◽  
Atmospheric Modeling ◽  
Cloud Formation ◽  
Cold Pool ◽  
Large Temperature ◽  
Mixing Ratio ◽  
Air Masses ◽  
Central Amazon ◽  
Mixing Ratios

Abstract. In the period between 9 and 11 July 2014, a friagem event reached the Amazon region. On 11 July, the southwest flow related to the friagem converged with the easterly winds in the central Amazon. The interaction between these two distinct air masses formed a convection band, which intensified over the Manaus region and the Amazon Tall Tower Observatory (ATTO) site. The satellite images show the evolution of convective activity on 11 July, which led to 21 mm of precipitation at the ATTO site. Moreover, the arrival of the friagem caused a sudden drop in temperature and a predominance of southerly winds, which could be seen in Porto Velho between 7 and 8 July and in Manaus and the ATTO site from 9 to 11 July. The results of ERA-Interim reanalysis and Brazilian developments on the Regional Atmospheric Modeling System (BRAMS) simulations show that this friagem event coming from the southwest, carries a mass of air with higher O3 and NO2 mixing ratios and lower CO mixing ratio compared to the air masses present in the central Amazon. At Lake Balbina, the friagem intensifies the local circulations, such as the breeze phenomena. In the Manaus region and at the ATTO site, the main effects of the friagem event are a decrease in the incoming solar radiation (due to intense cloud formation), a large temperature drop and a distinct change in surface O3 and CO2 mixing ratios. As the cold air of the friagem was just in the lower 500 m the most probable cause of this change is that a cold pool above the forest prevented vertical mixing causing accumulation of CO2 from respiration and very low O3 mixing ratio due to photochemistry reduction and limited mixing within the boundary layer.

scholarly journals Radar Reflectivity–Based Estimates of Mixed Layer Depth

2009 ◽  
Vol 26 (2) ◽  
pp. 229-239 ◽  
Author(s):  
P. L. Heinselman ◽  
P. L. Spencer ◽  
K. L. Elmore ◽  
D. J. Stensrud ◽  
R. M. Hluchan ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Weather Conditions ◽  
Radar Reflectivity ◽  
Oklahoma City ◽  
Mixing Ratio ◽  
Mixing Height ◽  
Layer Depth ◽  
Maximum Reflectivity ◽  
Water Vapor Mixing Ratio

Abstract This study investigates the potential for estimating mixed layer depth by taking advantage of the radial gradients in the radar reflectivity field produced by the large vertical gradients in water vapor mixing ratio that are characteristic of the mixing height. During the day, this relationship often results in a ring of maximum reflectivity observed to progress radially outward from the radar as mixed layer depth increases. A comparison of mixed layer depths estimated from the Oklahoma City WSR-88D (KTLX) with those estimated from a nearby 915-MHz profiler reveals that mixed layer depths from the WSR-88D are slightly too high (up to 0.3 km) during the first three hours of the diurnal cycle, nearly unbiased midday, and slightly too low (0.2 km or less) thereafter. The procedure estimates mixed layer depths only during the daytime hours from 1300 to 2300 UTC. The weather conditions for the 17 days studied were fairly quiescent, with sunny skies and light winds.

scholarly journals A New Method for Correcting Deviation of Volatiles Content and Chamber Pressure for Single Base Propellant

2021 ◽  
Author(s):  
Haider Elbasher ◽  
Ahmed Ibrahim
Keyword(s):  
New Method ◽  
Chamber Pressure ◽  
Special Treatment ◽  
Mixing Ratio ◽  
Volatile Content ◽  
Standard Requirement ◽  
Single Base ◽  
Mixing Ratios ◽  
Significant Difference ◽  
Final Batch

In this study, special treatment was applied to two production batches of single-base propellant to correct three of the most important properties in the final product. These properties are internal and external volatile content (IV%, EV% respectively) and chamber pressure, the special treatments depend on mixing two batches with different percentages of mixing starting with sieving and ended with blending to guarantee the homogeneity of the final batch. The batches under study (A and B), batch A with (IV% 0.53%) which must be not less than 0.6%, so it deviated from standard requirement and Bach B with (IV =0.88%), the treatment applied for these batches to generate (C and D) batches. Batch C was a mixture composed of (25% of batch A and 0.75% of batch B). batch D was a mixture composed of (50%batchA and 50% of batch B). Six samples were subjected to sieving and blending according to calculations to correct internal and external volatile content and chamber pressure. For all samples lab, ballistics test, and executive calculations were done. After the test observed that no significant difference between the test and the results of calculations for all samples with different mixing ratios either volatiles content or chamber pressure so according to the result achieved the procedure (Method) was dependable for correcting the deviation of volatiles content and chamber pressure. The selectivity of the optimum mixing ratio can be controlled by using the equation used in this study. The importance of this study in reducing material losses due to the non-conformity of the final product with the specification.

scholarly journals Assessment of Tropospheric Concentrations of NO2 from the TROPOMI/Sentinel-5 Precursor for the Estimation of Long-Term Exposure to Surface NO2 over South Korea

2021 ◽  
Vol 13 (10) ◽  
pp. 1877
Author(s):  
Ukkyo Jeong ◽  
Hyunkee Hong
Keyword(s):  
South Korea ◽  
Spatial Resolution ◽  
Atmospheric Composition ◽  
Mixing Ratio ◽  
Mean Values ◽  
Mixing Ratios ◽  
Tropospheric No2 ◽  
Korean Ministry ◽  
Surface Mixing ◽  
Rural Sites

Since April 2018, the TROPOspheric Monitoring Instrument (TROPOMI) has provided data on tropospheric NO2 column concentrations (CTROPOMI) with unprecedented spatial resolution. This study aims to assess the capability of TROPOMI to acquire high spatial resolution data regarding surface NO2 mixing ratios. In general, the instrument effectively detected major and moderate sources of NO2 over South Korea with a clear weekday–weekend distinction. We compared the CTROPOMI with surface NO2 mixing ratio measurements from an extensive ground-based network over South Korea operated by the Korean Ministry of Environment (SKME; more than 570 sites), for 2019. Spatiotemporally collocated CTROPOMI and SKME showed a moderate correlation (correlation coefficient, r = 0.67), whereas their annual mean values at each site showed a higher correlation (r = 0.84). The CTROPOMI and SKME were well correlated around the Seoul metropolitan area, where significant amounts of NO2 prevailed throughout the year, whereas they showed lower correlation at rural sites. We converted the tropospheric NO2 from TROPOMI to the surface mixing ratio (STROPOMI) using the EAC4 (ECMWF Atmospheric Composition Reanalysis 4) profile shape, for quantitative comparison with the SKME. The estimated STROPOMI generally underestimated the in-situ value obtained, SKME (slope = 0.64), as reported in previous studies.

scholarly journals One-Year Characterization and Reactivity of Isoprene and Its Impact on Surface Ozone Formation at A Suburban Site in Guangzhou, China

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 201 ◽  
Author(s):  
Yu Zou ◽  
Xue Jiao Deng ◽  
Tao Deng ◽  
Chang Qin Yin ◽  
Fei Li
Keyword(s):  
Surface Ozone ◽  
Atmospheric Composition ◽  
Anthropogenic Factors ◽  
Mixing Ratio ◽  
Night Time ◽  
Subtropical Zone ◽  
Guangzhou City ◽  
Mixing Ratios ◽  
One Year ◽  
Suburban Site

Isoprene has a potentially large effect on ozone (O3) formation in the subtropical, highly polluted city of Guangzhou. Online measurements of isoprene in Guangzhou city are scarce; thus, isoprene levels were monitored for one year at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, using an online gas chromatography-flame ionization detector (GC–FID) system to investigate the characterization and reactivity of isoprene and its effect on the O3 peak profile in different seasons. The results showed that the daily average mixing ratios of isoprene at GPACS were 0.40, 2.20, 1.40, and 0.13 mixing ratio by volume (ppbv) in spring, summer, autumn, and winter, respectively. These values were considerably higher than the mixing ratios of isoprene in the numerous other subtropical and temperate cities around the world. Furthermore, isoprene ranked first with regard to O3 formation potential (OFP) and propylene-equivalent mixing ratio among 56 measured non–methane hydrocarbons (NMHCs). The ratios of isoprene to cis-2-butene, an exhaust tracer, were determined to estimate the fractions of biogenic and anthropogenic emissions. The results revealed a much greater contribution from biogenic than anthropogenic factors during the daytime in all four seasons. In addition, night-time isoprene emissions were mostly associated with vehicles in winter, and the residual isoprene that remained after photochemical loss during the daytime also persisted into the night. The high levels of isoprene in summer and autumn may cause the strong and broad peaks of the O3 profile because of its association with the most favorable meteorological conditions (e.g., high temperature and intense solar radiation) and the highest OH mixing ratio, which could affect human health by exposing people to a high O3 mixing ratio for prolonged periods. The lower mixing ratios of isoprene resulted in a weak and sharp peak in the O3 profile in both spring and winter. The high level of isoprene in the subtropical zone could accentuate its large impact on atmospheric oxidant capacity and air quality in Guangzhou city.

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