scholarly journals Developing a long-term high-resolution winter fog climatology over south Asia using satellite observations from 2002 to 2020

2021 ◽  
Author(s):  
Manoj Singh ◽  
RITESH GAUTAM
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Effective Radius ◽  
Satellite Observations ◽  
Difference Threshold ◽  
Near Surface ◽  
Gangetic Plains ◽  
Dense Fog ◽  
Fog Detection

The vast Indo-Gangetic Plains (IGP) south of the Himalaya are subject to dense fog every year during winter months (December-January), severely disrupting rail, air and public transport of millions of people living in northern India, Pakistan, Nepal and Bangladesh. Air pollution combined with high moisture availability in the shallow boundary layer, are important factors affecting the persistence and widespread nature of fog over the IGP. Despite the environmental significance and impacts on the public at-large, an in depth understanding of the long-term spatial-temporal distribution of the south Asian fog, is presently not available in the literature. We utilize infrared remote sensing techniques to develop a high-resolution (≈1 km x 1 km) fog detection climatology over the past two decades (2002 – 2020), using Aqua/MODIS satellite observations. A dynamic brightness temperature difference threshold (involving 3.96 μm and 11.03 μm bands) for nighttime fog detection is constructed based on systematic radiative transfer simulations involving cloud effective radius, cloud top height, cloud optical depth and satellite viewing geometry. Our satellite-based fog detection is consistent with theoretical simulations of fog characterization and is also found to be well-correlated with near-surface visibility observations of dense fog (r = 0.87, p-value << 0.01). We also provide satellite-derived nighttime estimates of fog/low-cloud effective radius which is in general agreement with the operational daytime MODIS cloud data product and limited in situ observations. In terms of fog frequency, the IGP is relatively uniformly covered by widespread fog occurrences with the largest frequency found in the low-lying Terai region, bordering India and Nepal, which is also consistently observed in our daytime fog detection results over the last two decades. Additionally, the interannual variations in fog occurrences track closely with that of relative humidity in the IGP, which is associated with shallow boundary layer conditions during winter-time favoring the formation and persistence of fog. Overall, these long-term satellite-derived results present new high-resolution data and insights into the dense and often intense winter fog occurrences which routinely engulf the entire stretch of the Indo-Gangetic Plains and cause significant degradation to ground visibility in one of the world’s most densely populated regions.

scholarly journals Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern

2007 ◽  
Vol 7 (12) ◽  
pp. 3129-3142 ◽  
Author(s):  
T. Wagner ◽  
O. Ibrahim ◽  
R. Sinreich ◽  
U. Frieß ◽  
R. von Glasow ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Vertical Mixing ◽  
Satellite Observations ◽  
Research Vessel ◽  
Optical Absorption Spectroscopy ◽  
Back Trajectory ◽  
First Year ◽  
Polar Regions ◽  
Near Surface

Abstract. We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. Outside the first year sea ice belt, typically low BrO concentrations were found. Based on back trajectory calculations we find a positive correlation between the observed BrO differential slant column densities (ΔSCDs) and the duration for which the air masses had been in contact with the sea ice surface prior to the measurement. While we can not completely rule out that in several cases the highest BrO concentrations might be located close to the ground, our observations indicate that the maximum BrO concentrations might typically exist in a (possibly extended) layer around the upper edge of the boundary layer. Besides the effect of a decreasing pH of sea salt aerosol with altitude and therefore an increase of BrO with height, this finding might be also related to vertical mixing of air from the free troposphere with the boundary layer, probably caused by convection over the warm ocean surface at polynyas and cracks in the ice. Strong vertical gradients of BrO and O3 could also explain why we found enhanced BrO levels almost continuously for the observations within the sea ice. Based on our estimated BrO profiles we derive BrO mixing ratios of several ten ppt, which is slightly higher than many existing observations. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. From detailed radiative transfer simulations we find that MAX-DOAS observations are up to about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. For large periods of our measurements the solar elevation was very low or even below the horizon. For such conditions, most reactive Br-compounds might exist as Br2 molecules and ozone destruction and the removal of reactive bromine compounds might be substantially reduced.

scholarly journals Development and evaluation of CO<sub>2</sub> transport in MPAS-A v6.3

2021 ◽  
Vol 14 (5) ◽  
pp. 3037-3066
Author(s):  
Tao Zheng ◽  
Sha Feng ◽  
Kenneth J. Davis ◽  
Sandip Pal ◽  
Josep-Anton Morguí
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Regional Scale ◽  
Global Scale ◽  
Transport Processes ◽  
Global Model ◽  
Total Carbon ◽  
Spatial Structures ◽  
Near Surface ◽  
Co2 Transport

Abstract. Chemistry transport models (CTMs) play an important role in understanding fluxes and atmospheric distribution of carbon dioxide (CO2). They have been widely used for modeling CO2 transport through forward simulations and inferring fluxes through inversion systems. With the increasing availability of high-resolution observations, it has been become possible to estimate CO2 fluxes at higher spatial resolution. In this work, we implemented CO2 transport in the Model for Prediction Across Scales – Atmosphere (MPAS-A). The objective is to use the variable-resolution capability of MPAS-A to enable a high-resolution CO2 simulation in a limited region with a global model. Treating CO2 as an inert tracer, we implemented in MPAS-A (v6.3) the CO2 transport processes, including advection, vertical mixing by boundary layer scheme, and convective transport. We first evaluated the newly implemented model's tracer mass conservation and then its CO2 simulation accuracy. A 1-year (2014) MPAS-A simulation is evaluated at the global scale using CO2 measurements from 50 near-surface stations and 18 Total Carbon Column Observing Network (TCCON) stations. The simulation is also compared with two global models: National Oceanic and Atmospheric Administration (NOAA) CarbonTracker v2019 (CT2019) and European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). A second set of simulation (2016–2018) is used to evaluate MPAS-A at regional scale using Atmospheric Carbon and Transport – America (ACT-America) aircraft CO2 measurements over the eastern United States. This simulation is also compared with CT2019 and a 27 km WRF-Chem simulation. The global-scale evaluations show that MPAS-A is capable of representing the spatial and temporal CO2 variation with a comparable level of accuracy as IFS of similar horizontal resolution. The regional-scale evaluations show that MPAS-A is capable of representing the observed atmospheric CO2 spatial structures related to the midlatitude synoptic weather system, including the warm versus cold sector distinction, boundary layer to free troposphere difference, and frontal boundary CO2 enhancement. MPAS-A's performance in representing these CO2 spatial structures is comparable to the global model CT2019 and regional model WRF-Chem.

Boundary Layer and Surface Verification of the High-Resolution Rapid Refresh, Version 3

2020 ◽  
Vol 35 (6) ◽  
pp. 2255-2278
Author(s):  
Robert G. Fovell ◽  
Alex Gallagher
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Wind Speed ◽  
Prediction Models ◽  
Weather Prediction ◽  
Potential Temperature ◽  
Ground Level ◽  
Systematic Errors ◽  
Radiosonde Data ◽  
Near Surface

AbstractWhile numerical weather prediction models have made considerable progress regarding forecast skill, less attention has been paid to the planetary boundary layer. This study leverages High-Resolution Rapid Refresh (HRRR) forecasts on native levels, 1-s radiosonde data, and (primarily airport) surface observations across the conterminous United States. We construct temporally and spatially averaged composites of wind speed and potential temperature in the lowest 1 km for selected months to identify systematic errors in both forecasts and observations in this critical layer. We find near-surface temperature and wind speed predictions to be skillful, although wind biases were negatively correlated with observed speed and temperature biases revealed a robust relationship with station elevation. Above ≈250 m above ground level, below which radiosonde wind data were apparently contaminated by processing, biases were small for wind speed and potential temperature at the analysis time (which incorporates sonde data) but became substantial by the 24-h forecast. Wind biases were positive through the layer for both 0000 and 1200 UTC, and morning potential temperature profiles were marked by excessively steep lapse rates that persisted across seasons and (again) exaggerated at higher elevation sites. While the source or cause of these systematic errors are not fully understood, this analysis highlights areas for potential model improvement and the need for a continued and accessible archive of the data that make analyses like this possible.

scholarly journals Evaluation of a forest parameterization to improve boundary layer flow simulations over complex terrain

2021 ◽  
Author(s):  
Julian Quimbayo-Duarte ◽  
Johannes Wagner ◽  
Norman Wildmann ◽  
Thomas Gerz ◽  
Juerg Schmidli
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Wind Speed ◽  
Complex Terrain ◽  
Grid Spacing ◽  
Short Term ◽  
Valley Wind ◽  
Layer Flow ◽  
Horizontal Grid

Abstract. We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather research and forecasting model using its large eddy simulation mode (WRF-LES). The short-term high resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 hours and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.

scholarly journals Profiling tropospheric CO<sub>2</sub> using the Aura TES and TCCON instruments

2012 ◽  
Vol 5 (3) ◽  
pp. 4495-4534 ◽  
Author(s):  
L. Kuai ◽  
J. Worden ◽  
S. Kulawik ◽  
K. Bowman ◽  
S. Biraud ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Near Infrared ◽  
Lower Troposphere ◽  
Total Carbon ◽  
Near Surface ◽  
Sources And Sinks ◽  
Global Carbon Budget ◽  
Regional Fluxes ◽  
Total Column

Abstract. Monitoring the global distribution and long-term variations of CO2 sources and sinks is required for characterizing the global carbon budget. Although total column measurements will be useful for estimating large regional fluxes, model transport error remains a significant error source, particularly for local sources and sinks. To improve the capability of estimating regional fluxes, we estimate near-surface CO2 values from ground-based near infrared (NIR) measurements with space-based thermal infrared (TIR) measurements. The NIR measurements are obtained from the Total Carbon Column Observing Network (TCCON) of solar measurements which provide an estimate of the total CO2 atmospheric column amount. Estimates of tropospheric CO2 that are co-located with TCCON are obtained by assimilating Tropospheric Emission Spectrometer (TES) free-tropospheric CO2 estimates into the GEOS-Chem model. Estimates of the boundary layer CO2 are obtained through simple subtraction, as the CO2 estimation problem is linear. We find that the calculated random uncertainties in total column and boundary layer estimates are consistent with actual uncertainties as compared to aircraft data. For the total column estimates the random uncertainty is about 0.55 ppm with a bias of −5.66 ppm, consistent with previously published results. After accounting for the total column bias, the bias in the boundary layer CO2 estimates is 0.26 ppm with a precision of 1.02 ppm This precision is sufficient for capturing the winter to summer variability of approximately 12 ppm in the lower troposphere; double the variability of the total column. This work shows that a combination of NIR and IR measurements can profile CO2 with the precisions and accuracy needed to quantify near-surface CO2 variability.

Wave-Induced Boundary Layer Separation in the Lee of the Medicine Bow Mountains. Part I: Observations*

2015 ◽  
Vol 72 (12) ◽  
pp. 4845-4863 ◽  
Author(s):  
Jeffrey R. French ◽  
Samuel J. Haimov ◽  
Larry D. Oolman ◽  
Vanda Grubišić ◽  
Stefano Serafin ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Vertical Plane ◽  
Boundary Layer Separation ◽  
Mountain Waves ◽  
Near Surface ◽  
Layer Separation ◽  
Medicine Bow Mountains ◽  
Vertical Winds ◽  
Wave Induced

Abstract Two cases of mountain waves, rotors, and the associated turbulence in the lee of the Medicine Bow Mountains in southeastern Wyoming are investigated in a two-part study using aircraft observations and numerical simulations. In Part I, observations from in situ instruments and high-resolution cloud radar on board the University of Wyoming King Air aircraft are presented and analyzed. Measurements from the radar compose the first direct observations of wave-induced boundary layer separation. The data from these two events show some striking similarities but also significant differences. In both cases, rotors were observed; yet one looks like a classical lee-wave rotor, while the other resembles an atmospheric hydraulic jump with midtropospheric gravity wave breaking aloft. High-resolution (30 × 30 m2) dual-Doppler syntheses of the two-dimensional velocity fields in the vertical plane beneath the aircraft reveal the boundary layer separation, the scale and structure of the attendant rotors, and downslope windstorms. In the stronger of the two events, near-surface winds upwind of the boundary layer separation reached 35 m s−1, and vertical winds were in excess of 10 m s−1. Moderate to strong turbulence was observed within and downstream of these regions. In both cases, the rotor extended horizontally 5–10 km and vertically 2–2.5 km. Horizontal vorticity within the rotor zone reached 0.2 s−1. Several subrotors from 500 to 1000 m in diameter were identified inside the main rotor in one of the cases. Part II presents a modeling study and investigates the kinematic structure and the dynamic evolution of these two events.

scholarly journals Complementarity of two high-resolution spatiotemporal methods (hydroacoustics and acoustic telemetry) for assessing fish distribution in a reservoir

2018 ◽  
Vol 20 ◽  
pp. 57-84
Author(s):  
C. Goulon ◽  
S. Westrelin ◽  
V. Samedy ◽  
R. Roy ◽  
J. Guillard ◽  
...  
Keyword(s):  
High Resolution ◽  
Time Window ◽  
Fish Distribution ◽  
Fish Length ◽  
Near Surface ◽  
Acoustic Methods ◽  
Bottom Depth ◽  
Individual Scale ◽  
Horizontal Beaming

The complementarity of two high-resolution spatiotemporal acoustic methods, telemetry and hydroacoustics, was evaluated during the same time window to obtain fish distribution in a canyon-shaped reservoir, the Bariousses Reservoir (France). These methods act at an individual scale for telemetry and a community scale for hydroacoustics. The temporal scales are also different: telemetry offers continuous and long-term monitoring while a “snapshot” view is given by hydroacoustics. Day and night hydroacoustic surveys were carried out in this reservoir, during a 24-hour period in spring, using vertical and near-surface horizontal beaming. During this time window, 11 adult fish (length: 22–57 cm) from three species (roach, perch, and pikeperch) were tracked by telemetry. Four metrics were calculated with data collected by application of the two methods: distance to the nearest bank, distance to the tributary, fish depth, and bottom depth at the location. The contrasting (distance to the nearest bank, bottom depth) or partially similar results (distance to the tributary, fish depth) can be explained by the limitations associated with each method. The results obtained with telemetry are very sensitive to the species composition and the size of the tagged fish. The number of fish located in the epibenthic areas of the reservoir can be underestimated by hydroacoustics. This preliminary case study highlights that these methods act in a complementary way and their simultaneous use can provide better information on fish spatial distribution.

scholarly journals Assimilating Surface Weather Observations from Complex Terrain into a High-Resolution Numerical Weather Prediction Model

2007 ◽  
Vol 135 (3) ◽  
pp. 1037-1054 ◽  
Author(s):  
Xingxiu Deng ◽  
Roland Stull
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Final Analysis ◽  
Numerical Weather Prediction Model ◽  
Near Surface ◽  
Weather Observations ◽  
Surface Weather ◽  
Grid Points

Abstract An anisotropic surface analysis method based on the mother–daughter (MD) approach has been developed to spread valley station observations to grid points in circuitous steep valleys. In this paper, the MD approach is further refined to allow spreading the mountain-top observations to grid points near neighboring high ridges across valleys. Starting with a 3D first guess from a high-resolution mesoscale model forecast, surface weather observations are assimilated into the boundary layer, and pseudo-upper-air data (interpolated from the coarser-resolution analyses from major operational centers) are assimilated into the free atmosphere. Incremental analysis updating is then used to incorporate the final analysis increments (the difference between the final analysis and the first guess) into a high-resolution numerical weather prediction model. The MD approaches (including one with shoreline refinement) are compared with other objective analysis methods using case examples and daily mesoscale real-time forecast runs during November and December 2004. This study further confirms that the MD approaches outperform the other methods, and that the shoreline refinement achieves better analysis quality than the basic MD approach. The improvement of mountain-top refinement over the basic MD approach increases with the percentage of mountain-top stations, which is usually low. Higher skill in predicting near-surface potential temperature is found when surface information is spread upward throughout the boundary layer instead of at only the bottom model level. The results show improved near-surface forecasts of temperature and humidity that are directly assimilated into the model, but poorer forecasts of near-surface winds and precipitation, which are not assimilated into the model.

scholarly journals The Effects of the Width of an Isolated Valley on Near-Surface Turbulence

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1330
Author(s):  
Sylvio Freitas ◽  
Frank Harms ◽  
Bernd Leitl
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Laser Doppler Velocimetry ◽  
Three Dimensional ◽  
Doppler Velocimetry ◽  
Constant Depth ◽  
Near Surface ◽  
Surface Flows ◽  
Surface Turbulence ◽  
Recirculation Zones

With the aim of ascertaining the effects of the widths (A) of valleys on near-surface turbulence, flows over an isolated symmetric three-dimensional valley of constant depth (H) and slopes are characterized in a large-boundary-layer wind tunnel. Starting at A = 4H, valley widths were systematically varied to A = 12H with constant increments of 2H. High-resolution laser-Doppler velocimetry measurements were made at several equivalent locations above each of the resulting valley geometries and compared with data from undisturbed flows over flat terrain. Flow separation caused by the first ridges generated inner-valley recirculation bubbles with lengths dependent on the valley widths. Secondary recirculation zones were also observed downstream from the crests of the second ridges. Results show that the width modifications exert the strongest effects on turbulence within the valleys and the vicinities of the second ridges. Above these locations, maximal magnitudes of turbulence are generally found for the larger width geometries. Furthermore, lateral turbulence overpowers the longitudinal counterparts nearest to the surface, with maximal gains occurring for the smaller widths. Our data indicate that valley widths are impactful on near-surface flows and should be considered together with other more established geometric parameters of influence.

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