Short-Period Modulations in Aerosol Optical Depths over the Central Himalayas: Role of Mesoscale Processes

2008 ◽  
Vol 47 (5) ◽  
pp. 1467-1475 ◽  
Author(s):  
U. C. Dumka ◽  
K. Krishna Moorthy ◽  
S. K. Satheesh ◽  
Ram Sagar ◽  
P. Pant

Abstract Multiyear measurements of spectral aerosol optical depths (AODs) were made at Manora Peak in the central Himalaya Range (29°22′N, 79°27′E, ∼1950 m above mean sea level), using a 10-channel multiwavelength solar radiometer for 605 days during January 2002–December 2004. The AODs at 0.5 μm were very low (≤0.1) in winter and increased steeply to reach high values (∼0.5) in summer. It was observed that monthly mean AODs vary significantly (by more than a factor of 6) from January to June. Strong short-period fluctuations (within a daytime) were observed in the AODs. Further investigations of this aspect have revealed that boundary layer dynamics plays a key role in transporting aerosols from the polluted valley region to higher altitudes, causing large contrast in AODs between forenoon and afternoon. The seasonal variations in AODs, while examined in conjunction with synoptic-scale wind fields, have revealed that the transport of dust aerosols from arid regions to the valley regions adjacent to the observational site and their subsequent transport upward by boundary layer dynamics are responsible for the summer increases.

2009 ◽  
Vol 66 (9) ◽  
pp. 2780-2795 ◽  
Author(s):  
Michael L. Waite ◽  
Boualem Khouider

Abstract A simplified model of intermediate complexity for convectively coupled gravity waves that incorporates the bulk dynamics of the atmospheric boundary layer is developed and analyzed. The model comprises equations for velocity, potential temperature, and moist entropy in the boundary layer as well as equations for the free tropospheric barotropic (vertically uniform) velocity and first two baroclinic modes of vertical structure. It is based on the multicloud model of Khouider and Majda coupled to the bulk boundary layer–shallow cumulus model of Stevens. The original multicloud model has a purely thermodynamic boundary layer and no barotropic velocity mode. Here, boundary layer horizontal velocity divergence is matched with barotropic convergence in the free troposphere and yields environmental downdrafts. Both environmental and convective downdrafts act to transport dry midtropospheric air into the boundary layer. Basic states in radiative–convective equilibrium are found and are shown to be consistent with observations of boundary layer and free troposphere climatology. The linear stability of these basic states, in the case without rotation, is then analyzed for a variety of tropospheric regimes. The inclusion of boundary layer dynamics—specifically, environmental downdrafts and entrainment of free tropospheric air—enhances the instability of both the synoptic-scale moist gravity waves and nonpropagating congestus modes in the multicloud model. The congestus mode has a preferred synoptic-scale wavelength, which is absent when a purely thermodynamic boundary layer is employed. The weak destabilization of a fast mesoscale wave, with a phase speed of 26 m s−1 and coupling to deep convection, is also discussed.


2010 ◽  
Vol 10 (7) ◽  
pp. 17815-17851 ◽  
Author(s):  
N. A. Brunsell ◽  
D. B. Mechem ◽  
M. C. Anderson

Abstract. The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variability under three different horizontal wind speeds are used in the analysis. The base case uses Landsat ETM imagery over the Cloud Land Surface Interaction Campaign (CLASIC) field site for 3 June 2007. Using wavelets, the surface fields are band-pass filtered in order to maintain the spatial mean and variances to length scales of 200 m, 1600 m, and 12.8 km as lower boundary conditions to the model. The simulations exhibit little variation in net radiation. Rather, a change in the partitioning of the surface energy between sensible and latent heat flux is responsible for differences in boundary layer dynamics. The sensible heat flux is dominant for intermediate surface length scales. For smaller and larger scales of surface heterogeneity, which can be viewed as being more homogeneous, the latent heat flux becomes increasingly important. The results reflect a general decrease of the Bowen ratio as the surface conditions transition from heterogeneous to homogeneous. Air temperature is less sensitive to surface heterogeneity than water vapor, which implies that the role of surface heterogeneity in modifying the local temperature gradients in order to maximize convective heat fluxes. More homogeneous surface conditions, on the other hand, tend to maximize latent heat flux. Scalar vertical profiles respond predictably to the partitioning of surface energy. Fourier spectra of the vertical wind speed, air temperature and specific humidity (w, T and q) and associated cospectra (w'T', w'q' and T'q'), however, are insensitive to the length scale of surface heterogeneity, but the near surface spectra are sensitive to the mean wind speed.


Author(s):  
Jordi Vilà-Guerau de Arellano ◽  
Edward G. Patton ◽  
Thomas Karl ◽  
Kees van den Dries ◽  
Mary C. Barth ◽  
...  

2015 ◽  
Vol 120 (9) ◽  
pp. 6329-6350 ◽  
Author(s):  
José Carlos Pintado‐Patiño ◽  
Alec Torres‐Freyermuth ◽  
Jack A. Puleo ◽  
Dubravka Pokrajac

2018 ◽  
Vol 18 (13) ◽  
pp. 10025-10038 ◽  
Author(s):  
Tirtha Banerjee ◽  
Peter Brugger ◽  
Frederik De Roo ◽  
Konstantin Kröniger ◽  
Dan Yakir ◽  
...  

Abstract. The role of secondary circulations has recently been studied in the context of well-defined surface heterogeneity in a semiarid ecosystem where it was found that energy balance closure over a desert–forest system and the structure of the boundary layer was impacted by advection and flux divergence. As a part of the CliFF (“Climate feedbacks and benefits of semi-arid forests”, a collaboration between KIT, Germany, and the Weizmann Institute, Israel) campaign, we studied the boundary layer dynamics and turbulent transport of energy corresponding to this effect in Yatir Forest situated in the Negev Desert in Israel. The forest surrounded by small shrubs presents a distinct feature of surface heterogeneity, allowing us to study the differences between their interactions with the atmosphere above by conducting measurements with two eddy covariance (EC) stations and two Doppler lidars. As expected, the turbulence intensity and vertical fluxes of momentum and sensible heat are found to be higher above the forest compared to the shrubland. Turbulent statistics indicative of nonlocal motions are also found to differ over the forest and shrubland and also display a strong diurnal cycle. The production of turbulent kinetic energy (TKE) over the forest is strongly mechanical, while buoyancy effects generate most of the TKE over the shrubland. Overall TKE production is much higher above the forest compared to the shrubland. The forest is also found to be more efficient in dissipating TKE. The TKE budget appears to be balanced on average both for the forest and shrubland, although the imbalance of the TKE budget, which includes the role of TKE transport, is found to be quite different in terms of diurnal cycles for the forest and shrubland. The difference in turbulent quantities and the relationships between the components of TKE budget are used to infer the characteristics of the turbulent transport of energy between the desert and the forest.


2014 ◽  
Vol 14 (15) ◽  
pp. 21101-21148 ◽  
Author(s):  
U. C. Dumka ◽  
D. G. Kaskaoutis ◽  
M. K. Srivastava ◽  
P. C. S. Devara

Abstract. Knowledge of light scattering and absorption properties of atmospheric aerosols is of vital importance in evaluating their types, sources and radiative forcing. This is of particular interest over the Gangetic–Himalayan (GH) region due to large aerosol loading over the plains and the uplift over the Himalayan range causing serious effects on atmospheric heating, glaciology and monsoon circulation. In this respect, Ganges Valley Aerosol Experiment (GVAX) was initiated over the region aiming to examine the aerosol properties, source regions, uplift mechanisms and aerosol-cloud interactions. The present study examines the temporal (monthly, seasonal) evolution of scattering (σsp) and absorption (σap) coefficients, their wavelength dependence, and the role of the Indo-Gangetic plains (IGP), boundary-layer dynamics (BLD) and long-range transport (LRT) in the aerosol uplift over the Himalayas. The measurements are performed at the elevated site Nainital via the Atmospheric Radiation Measurement Mobile Facility including several instruments (Nephelometer, Particle Soot Absorption Photometer, etc.) during June 2011 to March 2012. The σsp and σap exhibit a pronounced seasonal variation with monsoon low and post-monsoon (November) high, while the scattering wavelength exponent exhibits higher values during monsoon, in contrast to the absorption Ångström exponent which maximizes in December–March. The analysis is performed separately for particles bellow 10 and 1μm in diameter in order to examine the influence of the particle size on optical properties. The elevated-background measuring site provides the advantage of examining the LRT of natural and anthropogenic aerosols from the IGP and southwest Asia and the role of BLD in the aerosol lifting processes, while the aerosols are found to be well-mixed and aged-type dominant.


2021 ◽  
Author(s):  
Mariel Friberg ◽  
Dong Wu ◽  
James Carr ◽  
James Limbacher ◽  
Yufei Zou ◽  
...  

<p>Wildfires have posed increasing risks to human health and loss of life and property. Observations of wildfire remain limited, particularly the plume variables such as injection height and wind velocity critical to assessing wildfire impacts. Lack of adequate spatiotemporal coverage and measurement accuracy hinder predictability and initialization needed by weather and chemical transport models. The new observations from the emerging stereo wind and aerosol imaging techniques with LEO-GEO and GEO-GEO satellites offer an unprecedented opportunity to study wildfire dynamics and evolution processes in great detail. The diurnal coverage of the GEO-GEO winds stereo products (Carr et al., 2020, 2019, 2018) and the daytime coverage (and detail) of GEO multi-angle aerosol products (Limbacher et al., 2021; In Prep) can capture and further our understanding of intense wildfire dynamics (e.g., pyroCb), planetary boundary layer (PBL) variations, and direction of aerosol loadings. Using two new satellite-based stereoscopic tracking algorithms, we compare stereo observations directly with the Coupled WRF-CMAQ simulations (Zou et al., 2019) to diagnose the modeled plume injection height and wind velocity, and aerosol properties (Friberg et al., 2021; In Prep). The validated LEO-GEO winds and height algorithm provides plume dynamics data with an accuracy of 200 m vertical resolution for plume height and 0.5 m/s for plume speed. Using these stereo algorithms, we can determine if fire plumes stay within or shoot above PBL, which plays a critical role in plume transport and air quality. From the GEO-based observations of dynamic wildfire aerosol loading dispersion, height, and winds, we can track wildfire development at a sub-hourly frequency and capture extreme and/or rare events such as pyroCb that often occur in a short period of time and are largely missed by LEO satellites.</p><p> </p><p><strong>References:</strong></p><p>Carr, J.L., Wu, D.L., Daniels, J., Friberg, M.D., Bresky, W., Madani, H. “GEO-GEO Stereo-Tracking of Atmospheric Motion Vectors (AMVs) from the Geostationary Ring,” Remote Sensing, 2020 https://doi.org/10.3390/rs12223779</p><p>Carr, J.L., D.L. Wu, R.E. Wolfe, H. Madani, G. Lin, B. Tan, “Joint 3D-Wind Retrievals with Stereoscopic Views from MODIS and GOES,” Remote Sensing, 2019, Satellite Winds Special Issue https://doi.org/10.3390/rs11182100</p><p>Carr, J.L., D.L. Wu, M.A. Kelly, and J. Gong, “MISR-GOES 3D Winds: Implications for Future LEO-GEO and LEO-LEO Winds,” Remote Sensing, 2018, MISR Special Issue. https://www.mdpi.com/2072-4292/10/12/1885</p><p>Limbacher, J. A., R. A. Kahn, and M. D. Friberg “A Multi-Angle Geostationary Aerosol Retrieval Algorithm,” 2021 [<strong>In Prep</strong>].</p><p>Zou, Y., O’Neill, S.M., Larkin, N.K., Alvarado, E.C., Solomon, R., Mass, C., Liu, Y., Odman, M.T., Shen, H. “Machine learning based integration of high-resolution wildfire smoke simulations and observations for regional health impact assessment. International Journal of Environmental Research and Public Health, 2019. https://doi.org/10.3390/ijerph16122137</p><p>Friberg, M.D., Wu, D.L., Carr, J.L., Limbacher, J. A., Zou<sup>, </sup>Y., O’Neill, S. “Diurnal Observations of Wildfires Boundary Layer Dynamics and Aerosol Plume Convection using Stereo-Imaging Techniques,” 2021 [<strong>In Prep</strong>].</p>


2016 ◽  
Vol 141 ◽  
pp. 571-579 ◽  
Author(s):  
J.-C. Dupont ◽  
M. Haeffelin ◽  
J. Badosa ◽  
T. Elias ◽  
O. Favez ◽  
...  

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