A Stereo Photogrammetric Technique Applied to Orographic Convection

2007 ◽  
Vol 135 (6) ◽  
pp. 2265-2277 ◽  
Author(s):  
Joseph A. Zehnder ◽  
Jiuxiang Hu ◽  
Anshuman Razdan
Keyword(s):  
Doppler Radar ◽  
Focal Length ◽  
Deep Convection ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Maximum Height ◽  
Detailed Knowledge ◽  
Shallow Convection ◽  
Orographic Convection ◽  
Santa Catalina Mountains

Abstract This paper describes a technique for photogrammetric analysis of stereo pairs of images that is applied to the study of orographic convection. The technique is designed for use with digital images and assumes detailed knowledge of the camera properties (focal length and imaging chip) and that the position and orientation are known as a first guess. An iterative scheme using known landmarks on the frame is used to determine the camera orientation. The scheme is accurate to 10–100 m at a distance of 15 km from the camera pair. The transition from shallow to deep convection over the Santa Catalina Mountains in southern Arizona on 26 July 2005 is presented. The three-dimensional structure of the visible portion of the cloud is determined and compared with the composite reflectivity from the National Weather Service Weather Surveillance Radar-1988 Doppler radar and the tropopause height from the 1200 UTC sounding in Tucson, Arizona, providing additional validation of the scheme. The shallow to deep transition is characterized by tracking individual turrets and determining the maximum height of the cloud top. The cloud tops were limited to beneath 6000 m MSL for the first 1.5 h followed by the development of deep convection. The motion of the turrets and location of the eventual deep convection were consistent with the idea that moistening by shallow convection conditions the atmosphere for further development.

scholarly journals Observations of the 11 June Dryline during IHOP_2002—A Null Case for Convection Initiation

2006 ◽  
Vol 134 (1) ◽  
pp. 336-354 ◽  
Author(s):  
Huaqing Cai ◽  
Wen-Chau Lee ◽  
Tammy M. Weckwerth ◽  
Cyrille Flamant ◽  
Hanne V. Murphey
Keyword(s):  
Cross Sections ◽  
Doppler Radar ◽  
Mesoscale Model ◽  
Water Cycle ◽  
Deep Convection ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Middle Level ◽  
Dimensional Structure ◽  
Convection Initiation

Abstract The detailed analysis of the three-dimensional structure of a dryline observed over the Oklahoma panhandle during the International H2O Project (IHOP_2002) on 11 June 2002 is presented. High-resolution observations obtained from the National Center for Atmospheric Research Electra Doppler Radar (ELDORA), S-band dual-polarization Doppler radar (S-Pol), water vapor differential absorption lidar (DIAL) Lidar pour l'Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l'Eau (LEANDRE II; translated as Lidar for the Study of Aerosol–Cloud–Dynamics–Radiation Interactions and of the Water Cycle) as well as Learjet dropsondes are used to reveal the evolution of the dryline structure during late afternoon hours when the dryline was retreating to the northwest. The dryline reflectivity shows significant variability in the along-line direction. Dry air was observed to overrun the moist air in vertical cross sections similar to a density current. The updrafts associated with the dryline were 2–3 m s−1 and were able to initiate boundary-layer-based clouds along the dryline. The formation of this dryline was caused by high equivalent potential temperature air pushing northwestward toward a stationary front in the warm sector. Middle-level clouds with radar reflectivity greater than 18 dBZe near the dryline were detected by ELDORA. A roll boundary, which was associated with larger convergence and moisture content, was evident in the S-Pol data. It is found that the instability parameters most favorable for convection initiation were actually associated with the roll boundary, not the dryline. A storm was initiated near the roll boundary probably as a result of the combination of the favorable instability parameters and stronger upward forcing. It is noted that both the 11 June 2002 dryline and the roll boundary presented in this paper would not be identified if the special datasets from IHOP_2002 were not available. Although all model runs [fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), Meso Eta, and Rapid Update Cycle (RUC)] suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms. The reasons why the dryline failed to produce any storm inside the IHOP_2002 intensive observation region are discussed. Both synoptic-scale and mesoscale conditions that were detrimental to convection initiation in this case are investigated in great detail.

Evolution of the Vertical Thermodynamic Profile during the Transition from Shallow to Deep Convection during CuPIDO 2006*

2009 ◽  
Vol 137 (3) ◽  
pp. 937-953 ◽  
Author(s):  
Joseph A. Zehnder ◽  
Jiuxiang Hu ◽  
Anshuman Radzan
Keyword(s):  
Field Experiment ◽  
Gravity Waves ◽  
Deep Convection ◽  
Shallow Convection ◽  
Stable Layer ◽  
Dry Air ◽  
Low Level ◽  
Orographic Convection ◽  
Santa Catalina Mountains

Abstract The evolution of the vertical thermodynamic profile associated with two cases of deep orographic convection were studied with data from an instrumented aircraft, mobile surface based radiosondes, and stereo photogrammetric analyses. The data were collected during a field experiment [i.e., the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) experiment in 2006] performed over the Santa Catalina Mountains in southern Arizona. In both cases the vertical thermodynamic profile was modified in a way that supported subsequent deep convection. In one case, a midtropospheric stable layer was eroded through low-level warming and cooling at the cloud-top level that was likely due to an adiabatic adjustment of the profile through the action of gravity waves. In the second case, dry air aloft was moistened through the action of the shallow convection thus preventing the erosion of the convective turrets through entrainment of dry air. These cases illustrate mechanisms for convective conditioning of the atmosphere that may organize deep convection in general.

Atmospheric Factors Governing Banded Orographic Convection

2005 ◽  
Vol 62 (10) ◽  
pp. 3758-3774 ◽  
Author(s):  
Daniel J. Kirshbaum ◽  
Dale R. Durran
Keyword(s):  
Three Dimensional ◽  
Heavy Precipitation ◽  
Thermal Fluctuations ◽  
Dominant Mode ◽  
Vertical Shear ◽  
Dimensional Structure ◽  
Small Scale ◽  
Atmospheric Structure ◽  
Orographic Convection ◽  
Orographic Cloud

Abstract The three-dimensional structure of shallow orographic convection is investigated through simulations performed with a cloud-resolving numerical model. In moist flows that overcome a given topographic barrier to form statically unstable cap clouds, the organization of the convection depends on both the atmospheric structure and the mechanism by which the convection is initiated. Convection initiated by background thermal fluctuations embedded in the flow over a smooth mountain (without any small-scale topographic features) tends to be cellular and disorganized except that shear-parallel bands may form in flows with strong unidirectional vertical shear. The development of well-organized bands is favored when there is weak static instability inside the cloud and when the dry air surrounding the cloud is strongly stable. These bands move with the flow and distribute their cumulative precipitation evenly over the mountain upslope. Similar shear-parallel bands also develop in flows where convection is initiated by small-scale topographic noise superimposed onto the main mountain profile, but in this case stronger circulations are also triggered that create stationary rainbands parallel to the low-level flow. This second dominant mode, which is less sensitive to the atmospheric structure and the strength of forcing, is triggered by lee waves that form over small-scale topographic bumps near the upstream edge of the main orographic cloud. Due to their stationarity, these flow-parallel bands can produce locally heavy precipitation amounts.

scholarly journals Relationships between Deep Convection Updraft Characteristics and Satellite-Based Super Rapid Scan Mesoscale Atmospheric Motion Vector–Derived Flow

2018 ◽  
Vol 146 (10) ◽  
pp. 3461-3480 ◽  
Author(s):  
Jason M. Apke ◽  
John R. Mecikalski ◽  
Kristopher Bedka ◽  
Eugene W. McCaul ◽  
Cameron R. Homeyer ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Deep Convection ◽  
Motion Vector ◽  
Three Dimensional ◽  
Radar Data ◽  
Severe Weather ◽  
Lightning Flash ◽  
Rapid Scan ◽  
Total Lightning ◽  
The Relationship

Abstract Rapid acceleration of cloud-top outflow near vigorous storm updrafts can be readily observed in Geostationary Operational Environmental Satellite-14 (GOES-14) super rapid scan (SRS; 60 s) mode data. Conventional wisdom implies that this outflow is related to the intensity of updrafts and the formation of severe weather. However, from an SRS satellite perspective, the pairing of observed expansion and updraft intensity has not been objectively derived and documented. The goal of this study is to relate GOES-14 SRS-derived cloud-top horizontal divergence (CTD) over deep convection to internal updraft characteristics, and document evolution for severe and nonsevere thunderstorms. A new SRS flow derivation system is presented here to estimate storm-scale (<20 km) CTD. This CTD field is coupled with other proxies for storm updraft location and intensity such as overshooting tops (OTs), total lightning flash rates, and three-dimensional flow fields derived from dual-Doppler radar data. Objectively identified OTs with (without) matching CTD maxima were more (less) likely to be associated with radar-observed deep convection and severe weather reports at the ground, suggesting that some OTs were incorrectly identified. The correlation between CTD magnitude, maximum updraft speed, and total lightning was strongly positive for a nonsupercell pulse storm, and weakly positive for a supercell with multiple updraft pulses present. The relationship for the supercell was nonlinear, though larger flash rates are found during periods of larger CTD. Analysis here suggests that combining CTD with OTs and total lightning could have severe weather nowcasting value.

A Numerical Study of the Evolving Convective Boundary Layer and Orographic Circulation around the Santa Catalina Mountains in Arizona. Part II: Interaction with Deep Convection

2010 ◽  
Vol 138 (9) ◽  
pp. 3603-3622 ◽  
Author(s):  
J. Cory Demko ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Surface Flow ◽  
Convective Boundary ◽  
Convergence Line ◽  
Orographic Convection ◽  
Present Part ◽  
Santa Catalina Mountains

Abstract This is the second part of a study that examines the daytime evolution of the thermally forced boundary layer (BL) circulation over a relatively isolated mountain, about 30 km in diameter and 2 km high, and its interaction with locally initiated deep convection by means of numerical simulations validated with data collected in the 2006 Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) field campaign in southeastern Arizona. Part I examined the BL circulation in cases with, at most, rather shallow orographic cumulus (Cu) convection; the present part addresses deep convection. The results are based on output from version 3 of the Weather Research and Forecasting model run at a horizontal resolution of 1 km. The model output verifies well against CuPIDO observations. In the absence of Cu convection, the thermally forced (solenoidal) circulation is largely contained within the BL over the mountain. Thunderstorm development deepens this BL circulation with inflow over the depth of the BL and outflow in the free troposphere aloft. Primary deep convection results from destabilization over elevated terrain and tends to be triggered along a convergence line, which arises from the solenoidal circulation but may drift downwind of the terrain crest. While the solenoidal anabatic flow converges moisture over the mountain, it also cools the air. Thus, a period of suppressed anabatic flow following a convective episode, at a time when surface heating is still intense, can trigger new and possibly deeper convection. The growth of deep convection may require enhanced convergent flow in the BL, but this is less apparent in the mountain-scale surface flow signal than the decay of orographic convection. A budget study over the mountain suggests that the precipitation efficiency of the afternoon convection is quite low, ~10% in this case.

A Numerical Study of the Evolving Convective Boundary Layer and Orographic Circulation around the Santa Catalina Mountains in Arizona. Part I: Circulation without Deep Convection

2010 ◽  
Vol 138 (5) ◽  
pp. 1902-1922 ◽  
Author(s):  
J. Cory Demko ◽  
Bart Geerts
Keyword(s):  
Boundary Layer ◽  
Numerical Study ◽  
Deep Convection ◽  
Weather Research And Forecasting ◽  
Return Flow ◽  
Convective Boundary ◽  
Warm Anomaly ◽  
Orographic Convection ◽  
Upper Level ◽  
Santa Catalina Mountains

Abstract The daytime evolution of the thermally forced boundary layer (BL) circulation over an isolated mountain, about 30 km in diameter and 2 km high, is examined by means of numerical simulations validated with data collected in the Cumulus Photogrammetric, In Situ, and Doppler Observations (CuPIDO) field campaign. Two cases are presented, one remains cloud free in the simulations, and the second produces orographic convection just deep enough to yield a trace of precipitation. The Weather Research and Forecasting version 3 simulations, at a resolution of 1 km, compare well with CuPIDO observations. The simulations reveal a solenoidal circulation mostly contained within the convective BL, but this circulation and especially its upper-level return flow branch are not immediately apparent since they are overwhelmed by BL thermals. A warm anomaly forms over the high terrain during the day, but it is rather shallow and does not extend over the depth of the convective BL, which bulges over the mountain. Low-level mountain-scale convergence (MSC), driven by an anabatic pressure gradient, deepens during the day. Even relatively shallow and relatively small cumulus convection can temporarily overwhelm surface MSC by cloud shading and convective downdraft dynamics. In the evening drainage flow develops near the surface before the anabatic forcing ceases, and anabatic flow is still present in the residual mixed layer, decoupled from the surface. The interaction of the boundary layer circulation with deep orographic convection is examined in Part II of this study.

Unusually Long Duration, Multiple-Doppler Radar Observations of a Front in a Convective Boundary Layer

2007 ◽  
Vol 135 (1) ◽  
pp. 93-117 ◽  
Author(s):  
John R. Stonitsch ◽  
Paul M. Markowski
Keyword(s):  
Boundary Layer ◽  
Density Gradient ◽  
Doppler Radar ◽  
Deep Convection ◽  
Three Dimensional ◽  
Horizontal Wind ◽  
Normal Density ◽  
Wind Fields ◽  
Convective Boundary ◽  
Convection Initiation

Abstract Dual-Doppler observations acquired by a network of mobile radars deployed in the Oklahoma panhandle on 3 June 2002 are used to document the kinematic structure and evolution of a front. The data were collected during the International H2O Project on a mission to study the initiation of deep convection. Synchronized scanning allowed for the synthesis of three-dimensional wind fields for nearly 5.5 h of the 1557–0000 UTC period. The front initially moved southward as a cold front, stalled, and later retreated northward as a warm front. Deep convection failed to be initiated along the front. In situ thermodynamic measurements obtained by a mobile mesonet were used to document changes in the density gradient at the surface. This paper examines the relationships among the changes in baroclinity, the thermally direct frontal circulation, updraft intensity, alongfront updraft variability, and the intensity of vortices along the front. Increases in the front-normal density gradient tended to be associated with increases in the thermally direct frontal circulation, as expected. Increases in the front-normal density gradient were also associated with an increase in the tilt of the frontal updraft as well as an increase in the contiguity of the updraft along the front, termed the “slabularity.” During periods when the front-normal density gradient and associated thermally direct frontal circulation were weak, the kinematic fields were dominated by boundary layer convection and the slabularity of the front was reduced. Intensification of the front-normal density gradient was accompanied by an increase in the horizontal wind shear and the intensity of vortices that were observed along the front. The vortices modulated the vertical velocity field along the front and therefore the slabularity, too. Thus, although the slabularity was a strong function of the strength of the thermally direct frontal circulation, the slabularity appeared to be modified by vortices in complex ways. Possible implications of the observations for convection initiation are also discussed, particularly with respect to updraft tilt and slabularity.

scholarly journals Characteristics of Precipitation Features and Annual Rainfall during the TRMM Era in the Central Andes

2014 ◽  
Vol 27 (11) ◽  
pp. 3982-4001 ◽  
Author(s):  
Karen I. Mohr ◽  
Daniel Slayback ◽  
Karina Yager
Keyword(s):  
System Development ◽  
Deep Convection ◽  
Arid Environment ◽  
Central Andes ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Annual Rainfall ◽  
Western Boundary ◽  
Maximum Height ◽  
Shallow Convection

Abstract The central Andes extends from 7° to 21°S, with its eastern boundary defined by elevation (1000 m and greater) and its western boundary by the coastline. The authors used a combination of surface observations, reanalysis, and the University of Utah Tropical Rainfall Measuring Mission (TRMM) precipitation features (PF) database to understand the characteristics of convective systems and associated rainfall in the central Andes during the TRMM era, 1998–2012. Compared to other dry (West Africa), mountainous (Himalayas), and dynamically linked (Amazon) regions in the tropics, the central Andes PF population was distinct from these other regions, with small and weak PFs dominating its cumulative distribution functions and annual rainfall totals. No more than 10% of PFs in the central Andes met any of the thresholds used to identify and define deep convection (minimum IR cloud-top temperatures, minimum 85-GHz brightness temperature, maximum height of the 40-dBZ echo). For most of the PFs, available moisture was limited (<35 mm) and instability low (<500 J kg−1). The central Andes represents a largely stable, dry to arid environment, limiting system development and organization. Hence, primarily short-duration events (<60 min) characterized by shallow convection and light to light–moderate rainfall rates (0.5–4.0 mm h−1) were found.

scholarly journals Life Cycle of a Mesoscale Circular Gust Front Observed by a C-Band Doppler Radar in West Africa

2011 ◽  
Vol 139 (5) ◽  
pp. 1370-1388 ◽  
Author(s):  
Marie Lothon ◽  
Bernard Campistron ◽  
Michel Chong ◽  
Fleur Couvreux ◽  
Françoise Guichard ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Life Cycle ◽  
Doppler Radar ◽  
Deep Convection ◽  
Convective System ◽  
Massachusetts Institute Of Technology ◽  
Shallow Convection ◽  
Multidisciplinary Analysis ◽  
Institute Of Technology ◽  
Gust Front

On 10 July 2006, during the Special Observation Period (SOP) of the African Monsoon Multidisciplinary Analysis (AMMA) campaign, a small convective system initiated over Niamey and propagated westward in the vicinity of several instruments activated in the area, including the Massachusetts Institute of Technology (MIT) C-band Doppler radar and the Atmospheric Radiation Measurement (ARM) mobile facility. The system started after a typical convective development of the planetary boundary layer. It grew and propagated within the scope of the radar range, so that its entire life cycle is documented, from the precluding shallow convection to its traveling gust front. The analysis of the observations during the transitions from organized dry convection to shallow convection and from shallow convection to deep convection lends support to the significant role played by surface temperature heterogeneities and boundary layer processes in the initiation of deep convection in semiarid conditions. The analysis of the system later in the day, of its growth and propagation, and of its associated density current allows the authors to estimate the wake available potential energy and demonstrate its capability to trigger deep convection itself. Given the quality and density of observations related to this case, and its typical and quasi-textbook characteristics, this is considered a prime case for the study of initiation and evolution of deep convection, and for testing their parameterizations in single-column models.

scholarly journals All-weather volume imaging of the boundary layer and troposphere using the MU radar

2004 ◽  
Vol 22 (5) ◽  
pp. 1407-1419 ◽  
Author(s):  
R. M. Worthington
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Dimensional Structure ◽  
Imaging Method ◽  
Radio Science ◽  
Convective Processes ◽  
Volume Imaging ◽  
Instruments And Techniques ◽  
Convective Cells

Abstract. This paper shows the first volume-imaging radar that can run in any weather, revealing the turbulent three-dimensional structure and airflow of convective cells, rain clouds, breaking waves and deep convection as they evolve and move. Precipitation and clear air can be volume-imaged independently. Birds are detected as small high-power echoes moving near horizontal, at different speeds and directions from background wind. The volume-imaging method could be used to create a real-time virtual-reality view of the atmosphere, in effect making the invisible atmosphere visible in any weather.Key words. Meteorology and atmospheric dynamics (convective processes, turbulence) – Radio science (instruments and techniques)

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