Spaceborne radar interferometric delay measurements were used to infer high-resolution maps of integrated atmospheric water vapor, which can be readily related to meteorological phenomena. Maps of ...the water vapor distribution associated with a precipitating cloud, a partly precipitating cold front, and horizontal convective rolls reveal quantitative measures that are not observed with conventional methods, and suggest that such radar observations can be used for forecasting and to study atmospheric dynamics.
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Abstract
The International H2O Project (IHOP_2002) was designed to sample the three-dimensional time-varying moisture field to better understand convective processes. Numerous research and ...operational water vapor measuring systems and retrievals, via in situ and remote sensing techniques, were operated in the U.S. Southern Great Plains from 13 May to 25 June 2002. This was done in combination with more traditional observations of wind and temperature. Convection initiation (CI) sampling strategies were designed to optimally employ the array of ground-based and airborne sensors to observe the processes leading to the development of deep, moist convection. This case study examines several clear-air features and their impact on CI on 12 June 2002. The supercells that developed produced damaging winds and hail. The clear-air, preconvective features included (i) a mesoscale low pressure region, (ii) a dryline, (iii) an old outflow boundary, (iv) the intersection of (ii) and (iii), (v) internal gravity waves, and (vi) horizontal convective rolls.
A unique combination of instruments was positioned to sample the preconvective environment on 12 June 2002. The Lidar pour l’Etude des Interactions Aérosols Nuages Dynamique Rayonnement et du Cycle de l’Eau (LEANDRE II) water vapor differential absorption lidar (DIAL), the airborne Electra Doppler Radar (ELDORA), and the Navy Research Laboratory (NRL) P3 aircraft in situ measurements provided information on the moisture and vertical velocity distribution within the boundary layer. Radiosondes, dropsondes, wind profilers, and an Atmospheric Emitted Radiance Interferometer (AERI) provided temperature, moisture, and wind profiling information. Although other ground-based sensors (i.e., S-band dual-polarization Doppler radar, Mobile Integrated Profiling System) were 50–150 km west of the CI area, they were useful for illustrating the boundary layer kinematics and reflectivity fields.
Results suggest that the mesolow and mesoscale boundaries, respectively, acted to enhance the low-level moisture advection and convergence in the CI region. While internal gravity waves were present and appeared to modulate water vapor along the old outflow boundary, they did not play an obvious role in CI in this case. Horizontal convective rolls were observed beneath the new storms that initiated and may have helped to focus the CI in this case.
RADAR IN ATMOSPHERIC SCIENCES AND RELATED RESEARCH Bluestein, Howard B.; Rauber, Robert M.; Burgess, Donald W. ...
Bulletin of the American Meteorological Society,
12/2014, Volume:
95, Issue:
12
Journal Article
Peer reviewed
Open access
To assist the National Science Foundation in meeting the needs of the community of scientists by providing them with the instrumentation and platforms necessary to conduct their research ...successfully, a meeting was held in late November 2012 with the purpose of defining the problems of the next generation that will require radar technologies and determining the suite of radars best suited to help solve these problems. This paper summarizes the outcome of the meeting: (i) Radars currently in use in the atmospheric sciences and in related research are reviewed. (ii) New and emerging radar technologies are described. (iii) Future needs and opportunities for radar support of high-priority research are discussed. The current radar technologies considered critical to answering the key and emerging scientific questions are examined. The emerging radar technologies that will be most helpful in answering the key scientific questions are identified. Finally, gaps in existing radar observing technologies are listed.
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A comprehensive observational dataset encompassing the entire temporal evolution of horizontal convective rolls was obtained for the first time. Florida, Illinois, and Kansas measurements from ...preroll conditions through the development of well-defined rolls to their dissipation were utilized to determine the factors influencing roll evolution. When the buoyancy flux reached a critical value of 35-50 W m super(-) super(2) , the first form of boundary layer convection resolved by radar was rolls. It was noted that two-dimensional convective rolls can evolve in a convective boundary layer in the absence of significant wind speed and shear. In fact, the value of wind speed or shear in itself did not seem to determine when or if rolls would form, although it did influence roll evolution. Well-defined, two-dimensional rolls only occurred while -z sub(i) /L, where z sub(i) is the convective boundary layer depth and L is the Monin-Obukhov length, was less than similar to 25, which is consistent with previous studies. As -z sub(i) /L increased throughout the day, either open cellular convection or unorganized boundary layer convection was the dominant clear-air convective mode. If the wind speed was low (mean boundary layer winds <3 m s super(-) super(1) or 10-m winds <2 m s super(-) super(1) ) during roll occurrences, rolls evolved into open cells. Alternatively, if the wind speed throughout the day was relatively high, rolls broke apart into random, unorganized convective elements. These are unprecedented observations of two-dimensional convection evolving into three-dimensional convection over land, which is analogous to laboratory convection where increased thermal forcing can produce a transition from two-dimensional to three-dimensional structures. Finally, the roll orientation was governed primarily by the mean convective boundary layer wind direction.
The Boundary Layer Evolution (BLE) missions of the International H sub(2)O Project (IHOP_2002) were designed to provide comprehensive observations of the distribution of water vapor in the quiescent ...boundary layer and its evolution during the early morning. The case study discussed in this paper presents detailed observations of the development of the boundary layer from before sunrise through to the period of growth of the mature convective boundary layer (CBL) during the 14 June 2002 BLE mission. The large number of remote sensing platforms, including the multiple instruments collocated at the Homestead Profiling Site, provided a detailed set of measurements of the growth and structure of the CBL. The observations describe the classic evolution of a daytime CBL, beginning with a shallow nocturnal boundary layer (NBL) below the remnants of the previous day's mixed layer, or residual layer. The vertical distribution of humidity in these layers during the early morning was affected by advection of dry air and by gravity waves. About an hour after sunrise a CBL developed, and gradually deepened with time as it mixed out the NBL and residual layer. The growth of the top of the CBL was particularly well observed because of the strong vertical gradients in temperature, humidity, and aerosol concentration. As the CBL deepened and the average CBL wind speed decreased, the mode of convective organization evolved from horizontal convective rolls to open-celled convection. A unique set of detailed measurements of the structure of the open cells was obtained from multiple instruments including the Doppler-on-Wheels radar, the Mobile Integrated Profiling System wind profiler, and the Scanning Raman lidar. They showed the relationship between open cells, thermals, mantle echoes, and the CBL top.
Abstract
East African countries benefit economically from the largest freshwater lake in Africa: Lake Victoria (LV). Around 30 million people live along its coastline, and 5.4 million people subsist ...on its fishing industry. However, more than 1000 fishermen die annually by high-wave conditions often produced by severe convective wind phenomena, which marks this lake one of the deadliest places in the world for hazardous weather impacts. The World Meteorological Organization launched the 3-yr High Impact Weather Lake System (HIGHWAY) project, with the main objective to reduce loss of lives and economic goods in the lake basin and improve the resilience of the local communities. The project conducted a field campaign in 2019 aiming to provide forecasters with high-resolution observations and to study the storm life cycle over the lake basin. The research discussed here used the S-band polarimetric Tanzania radar from the field campaign to investigate the diurnal cycle of the convective mode over the lake. We classified the lake storms occurring during the two wet seasons into six different convective modes and present their diurnal evolution, organization, and main radar-based attributes, thereby extending the knowledge of convection on the lake. The result is the creation of a “convection catalog for Lake Victoria,” using the operational forecast lake sectors, and defining the exact times for the different timeslots resulting from the HIGHWAY project for the marine forecast. This will inform methods to improve the marine operational forecasts for Lake Victoria, and to provide the basis for new standard operation procedures (SOP) for severe weather surveillance and warning.
Significance Statement
In this work we use new radar data over Lake Victoria, Africa, to study convective mode organization and its diurnal cycle over the lake. This work is of particular importance due to the numerous hazardous weather events and related accidents on the lake, including capsized boats, plane crashes, floods, and hailstorms on the shore settlements, that are responsible for a high annual fatality toll. Results of our analyses provide updated information for operational marine forecasts using relevant time segments and sectors of the lake to improve nowcasting operations in Lake Victoria.
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Data from the Convection and Precipitation/Electrification (CaPE) Experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and ...moisture within the convective boundary layer (CBL). Potential temperature variations were only about 0.5 K, while variations in water vapor mixing ratio values of 1.5-2.5 g kg super(-) super(1) were observed throughout the CBL. Using radar, aircraft, and sounding data, it is shown that horizontal convective rolls are the likely cause of these variabilities. The enhanced moisture occurred within the roll updraft regions, thus rolls were transporting moist air from the surface upward. The observed cloud-base heights, obtained from cloud photogrammetry, were produced from the highest moisture values within the roll updraft regions. Since the roll ascending branches contained moisture values that were most representative of the observed cloud-base heights, it is likely that measurements from within the roll updrafts would provide the best estimate of the potential for deep, moist convection.
Boundary layer evolution in response to diurnal forcing is manifested at the mesobeta and smaller scales of the atmosphere. Because this variability resides on subsynoptic scales, the potential ...influence upon convective storm environments is often not captured in coarse observational and modeling datasets, particularly for complex physical settings such as coastal regions. A detailed observational analysis of diurnally forced preconditioning for convective storm environments of South East Queensland, Australia (SEQ), during the Coastal Convective Interactions Experiment (2013–15) is presented. The observations used include surface-based measurements, aerological soundings, and dual-polarization Doppler radar. The sea-breeze circulation was found to be the dominant influence; however, profile modification by the coastward advection of the continental boundary layer was found to be an essential mechanism for favorable preconditioning of deep convection. This includes 1) enhanced moisture in the city of Brisbane, potentiality due to an urban heat island–enhanced land–sea thermal contrast, 2) significant afternoon warming and moistening above the sea breeze resulting from the advection of the inland convective boundary layer coastward under prevailing westerly flow coupled with the sea-breeze return flow, and 3) substantial variations in near-surface moisture likely associated with topography and land use. For the 27 November 2014 Brisbane hailstorm, which caused damages exceeding $1.5 billion Australian dollars (AUD), the three introduced diurnal preconditioning processes are shown to favor a mesoscale convective environment supportive of large hailstone growth. The hybrid high-precipitation supercell storm mode noted for this event and previous similar events in SEQ is hypothesized to be more sensitive to variations in near-surface and boundary layer instability in contrast to contemporary supercell storms.
Data from the Convection and Precipitation/Electrification (CaPE) project, as well as results from numerical simulations, are used to study horizontal convective rolls. The environmental conditions ...necessary for sustaining rolls and for influencing the aspect ratio, ratio of roll wavelength to convective boundary layer (CBL) depth, and orientation are examined. Observations and numerical model simulations both suggest that a moderate surface sensible heat flux and some vertical wind shear are necessary for roll existence. Unlike some previous studies, however, it is shown that rolls occurred within very low CBL shear conditions ( similar to 2 x 10 super(-) super(3) s super(-) super(1) ). In addition, the low-level (i.e., similar to 200 m) shear seems to be more important than the shear through the depth of the CBL in roll sustenance. The aspect ratio is shown to be proportional to the CBL instability, measured in terms of the Monin-Obukhov length. The roll orientation is similar to the wind direction at 10 m AGL, the CBL wind direction, the inversion-level wind direction, and the CBL shear direction. This is not surprising since there was very little directional shear observed within the CBL during CaPE.
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