Turbulent mixing in the planetary boundary layer (PBL) governs the vertical exchange of heat, moisture, momentum, trace gases, and aerosols in the surface–atmosphere interface. The PBL height (PBLH) ...represents the maximum height of the free atmosphere that is directly influenced by Earth’s surface. This study uses a multidata synthesis approach from an ensemble of multiple global datasets of radiosonde observations, reanalysis products, and climate model simulations to examine the spatial patterns of long-term PBLH trends over land between 60°S and 60°N for the period 1979–2019. By considering both the sign and statistical significance of trends, we identify large-scale regions where the change signal is robust and consistent to increase our confidence in the obtained results. Despite differences in the magnitude and sign of PBLH trends over many areas, all datasets reveal a consensus on increasing PBLH over the enormous and very dry Sahara Desert and Arabian Peninsula (SDAP) and declining PBLH in India. At the global scale, the changes in PBLH are significantly correlated positively with the changes in surface heating and negatively with the changes in surface moisture, consistent with theory and previous findings in the literature. The rising PBLH is in good agreement with increasing sensible heat and surface temperature and decreasing relative humidity over the SDAP associated with desert amplification, while the declining PBLH resonates well with increasing relative humidity and latent heat and decreasing sensible heat and surface warming in India. The PBLH changes agree with radiosonde soundings over the SDAP but cannot be validated over India due to lack of good-quality radiosonde observations.
PROBING THE FOG LIFE CYCLES IN THE NAMIB DESERT Spirig, Robert; Vogt, Roland; Larsrsen, Jarl Are ...
Bulletin of the American Meteorological Society,
12/2019, Letnik:
100, Številka:
12
Journal Article
Recenzirano
Odprti dostop
An intensive observation period was conducted in September 2017 in the central Namib, Namibia, as part of the project Namib Fog Life Cycle Analysis (NaFoLiCA). The purpose of the field campaign was ...to investigate the spatial and temporal patterns of the coastal fog that occurs regularly during nighttime and morning hours. The fog is often linked to advection of a marine stratus that intercepts with the terrain up to 100 km inland. Meteorological data, including cloud base height, fog deposition, liquid water path, and vertical profiles of wind speed/direction and temperature, were measured continuously during the campaign. Additionally, profiles of temperature and relative humidity were sampled during five selected nights with stratus/fog at both coastal and inland sites using tethered balloon soundings, drone profiling, and radiosondes. This paper presents an overview of the scientific goals of the field campaign; describes the experimental setup, the measurements carried out, and the meteorological conditions during the intensive observation period; and presents first results with a focus on a single fog event.
This paper provides an update and overview of the Center for Remote Sensing of Ice Sheets (CReSIS) radars and platforms, including representative results from these systems. CReSIS radar systems ...operate over a frequency range of 14–38 GHz. Each radar system's specific frequency band is driven by the required depth of signal penetration, measurement resolution, allocated frequency spectra, and antenna operating frequencies (often influenced by aircraft integration). We also highlight recent system advancements and future work, including (1) increasing system bandwidth; (2) miniaturizing radar hardware; and (3) increasing sensitivity. For platform development, we are developing smaller, easier to operate and less expensive unmanned aerial systems. Next-generation platforms will further expand accessibility to scientists with vertical takeoff and landing capabilities.
Abstract
During the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations-Cloud, Aerosol, and Complex Terrain Interactions ...(RELAMPAGO-CACTI) field experiments in 2018–19, an unprecedented number of balloon-borne soundings were collected in Argentina. Radiosondes were launched from both fixed and mobile platforms, yielding 2712 soundings during the period 15 October 2018–30 April 2019. Approximately 20% of these soundings were collected by highly mobile platforms, strategically positioned for each intensive observing period, and launching approximately once per hour. The combination of fixed and mobile soundings capture both the overall conditions characterizing the RELAMPAGO-CACTI campaign, as well as the detailed evolution of environments supporting the initiation and upscale growth of deep convective storms, including some that produced hazardous hail and heavy rainfall. Episodes of frequent convection were characterized by sufficient quantities of moisture and instability for deep convection, along with deep-layer vertical wind shear supportive of organized or rotating storms. A total of 11 soundings showed most unstable convective available potential energy (MUCAPE) exceeding 6000 J kg
−1
, comparable to the extreme instability observed in other parts of the world with intense deep convection. Parameters used to diagnose severe-storm potential showed that conditions were often favorable for supercells and severe hail, but not for tornadoes, primarily because of insufficient low-level wind shear. High-frequency soundings also revealed the structure and evolution of the boundary layer leading up to convection initiation, convectively generated cold pools, the South American low-level jet (SALLJ), and elevated nocturnal convection. This sounding dataset will enable improved understanding and prediction of convective storms and their surroundings in subtropical South America, as well as comparisons with other heavily studied regions such as the central United States that have not previously been possible.
Detection of subglacial lakes and interpretation their hydrological connectivity is of great importance to understanding the mass balance of Antarctic ice sheet. Over the past five decades, a large ...number of Radio Echo Sounding (RES) data has been collected in Antarctica. However, the identification of subglacial lakes based on RES data mainly relies on visual interpretation due to the lack of quantitative indicators for subglacial lakes distinguishing. To solve this problem, an automatic subglacial lakes detection method based on the reflective characteristics of B-scan echogram is proposed in this paper. Firstly, the echo strength of the original radar echogram is corrected for the dielectric attenuation and geometric spreading in the ice. Secondly, the original radar echogram is binarized to preserve the bright subglacial lake region, and the thickness of bright pixels is measured along the direction of A-scan. Thirdly, the thickness, the variance of the thickness in the neighbourhood and the corrected echo strength are used to obtain the response value for the subglacial lake. Finally, a threshold for the response value is determined to detect subglacial lakes. It is found that the proposed method can determine the location of the subglacial lake in Antarctica's Gamburtsev Province (AGAP) region with high accuracy.
Arctic Humidity Inversions Naakka, Tuomas; Nygård, Tiina; Vihma, Timo
Journal of climate,
05/2018, Letnik:
31, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The occurrence and characteristics of Arctic specific humidity inversions (SHIs) were examined on the basis of two reanalyses (ERA-Interim and JRA-55) and radiosonde sounding data from 2003 to 2014. ...Based on physical properties, the SHIs were divided into two main categories: SHIs below and above the 800-hPa level. Above the 800-hPa level, SHIs occurred simultaneously with relative humidity inversions and without the presence of a temperature inversion; these SHIs were probably formed when a moist air mass was advected over a dry air mass. SHIs below the 800-hPa level occurred simultaneously with temperature inversions in conditions of high relative humidity, which suggests that condensation had an important role in SHI formation. Below the 800-hPa level, SHI occurrence had a large seasonal and spatial variation, which depended on the surface heat budget. In winter, most SHIs were formed because of surface radiative cooling, and the occurrence of SHIs was high (even exceeding 90% of the time) on continents and over the ice-covered Arctic Ocean. In summer, the occurrence of SHIs was highest (70%–90%) over the coastal Arctic Ocean, where SHIs were generated by warm and moist air advection over a cold sea surface. In the reanalyses, the strongest SHIs occurred in summer over the Arctic Ocean. The comparisons between radiosonde soundings and the reanalyses showed that the main features of the seasonal and spatial variation of SHI occurrence and SHI strength were well represented in the reanalyses, but SHI strength was underestimated.
Rapidly depleting resources of surface water necessitate the exploration of groundwater reservoirs to cope with the water demand in Lahore and its periphery. For this purpose, a study was conducted ...to investigate groundwater depth, water quality, and subsurface lithology through Geo-electrical Resistivity Survey (ERS). Vertical electrical soundings (VES) at six (06) stations in the city of Lahore were performed using Schlumberger array. Apparent resistivity values were recorded at surface and processed with a computer software IPI2win to assess groundwater depth, quality, and subsurface formations. The VES resulted that the study area comprises of three layers. Top layer was determined as fill up to depth of 2 m followed by an unsaturated alluvium up to depth of 40 m, and the bottom layer was saturated alluvium up to the study depth of 100 m. The average water table depth was appeared to be at 39 m below the ground surface. The computed groundwater depths were also compared with the previous studies conducted in the proximity by different agencies in the past using destructive techniques and showed close resemblance. The study also shows that the groundwater up to depth of 100 m was having excess amount of total dissolved solids and was not drinkable as per quality standards set by the World Health Organization.
—Results of the interpretation of the archival vertical electrical sounding data from the Muya Basin of the Baikal Rift Zone are presented. Numerical modeling is carried out to verify the results. ...The permafrost zones are identified; the depths to the basement of the basin are estimated.
A mobile Shared Mobile Atmospheric Research and Teaching (SMART) radar was deployed in Hurricane Harvey and coordinated with the Corpus Christi, TX, WSR‐88D radar to retrieve airflow during landfall. ...Aerodynamic surface roughness estimates and a logarithmic wind profile assumption were used to project the 500‐m radar‐derived maximum wind field to near the surface. The logarithmic wind assumption was justified using radiosonde soundings taken within the storm, while the radar wind estimates were validated against an array of StickNets. For the data examined here, the radar projections had root‐mean‐squared error of 3.9 m/s and a high bias of 2.3 m/s. Mesovorticies in Harvey's eyewall produced the strongest radar‐observed winds. Given the wind analysis, Harvey was, at most, a Category 3 hurricane (50–58 m/s sustained winds) at landfall. This study demonstrates the utility of integrated remote and in situ observations in deriving spatiotemporal maps of wind maxima during hurricane landfalls.
Plain Language Summary
Measurements of extreme winds during hurricane landfall are difficult to obtain due to sparsely populated observing systems that cannot capture the complete distribution of the wind field. The wind fields are needed to refine building codes in hurricane prone areas and to delineate damage caused by wind versus water during poststorm assessment, particularly for insured losses. By using three‐dimensional winds retrieved from two ground‐based Doppler radars, the maximum wind distribution of Hurricane Harvey was analyzed. The radar winds were projected to the surface and validated against a network of anemometers, yielding close agreement. The analysis showed that Harvey was, at most, a Category 3 (sustained winds between 50 and 58 m/s) strength storm at landfall. Additionally, perturbations in the eyewall similar to the parent circulation of tornadic storms led to the strongest flow observed near the surface.
Key Points
Dual‐Doppler wind retrievals show that Harvey was, at most, a Category 3 hurricane at landfall
Mesovortices in the inner eyewall of Hurricane Harvey produced the strongest flow observed in the storm
Mobile Doppler radar and in situ surface and upper air networks can improve estimates of near‐surface winds during hurricane landfall
Hypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. ...Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean.
Plain Language Summary
The East and West Antarctic Ice Sheets meet at the inland termination of the Transantarctic Mountains. The ice sheets coalesce at a major ice divide, which could migrate and impact ice flow across large parts of Antarctica. A lack of satellite observations of ice flow and ice thickness has previously restricted characterization of this region, its glaciology, and its subglacial landscape. Our ice‐penetrating radar surveys reveal three deep subglacial valleys and mountainous subglacial topography beneath the ice divide. New measurements of ice flow evidence faster ice flow within these troughs than in the surrounding thinner ice. Were the ice sheet to shrink in size, an increase in the speed at which ice flows through these troughs could lead to the ice divide moving and increase the rate at which ice flows out from the center of Antarctica to its edges.
Key Points
Ice‐penetrating radar surveys provide ice stream onset zone boundary conditions in central Antarctica
Subglacial topography restricts hypothesized drawdown of the East Antarctic Ice Sheet through the bottleneck zone with West Antarctica
Variability of discharge through subglacial troughs could change the form and position of the southernmost West Antarctic ice divide
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