scholarly journals Advances and limitations of atmospheric boundary layer observations with GPS occultation over southeast Pacific Ocean

2012 ◽  
Vol 12 (2) ◽  
pp. 903-918 ◽  
Author(s):  
F. Xie ◽  
D. L. Wu ◽  
C. O. Ao ◽  
A. J. Mannucci ◽  
E. R. Kursinski
Keyword(s):  
Boundary Layer ◽  
Pacific Ocean ◽  
Atmospheric Boundary Layer ◽  
Temperature Inversion ◽  
Lower Percentage ◽  
Trade Wind ◽  
Sampling Errors ◽  
Wide Range ◽  
The Mean ◽  
The Difference

Abstract. The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific Ocean is featured with a strong temperature inversion and a sharp moisture gradient across the ABL top. The strong moisture and temperature gradients result in a sharp refractivity gradient that can be precisely detected by the Global Positioning System (GPS) radio occultation (RO) measurements. In this paper, the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect a wide range of ABL height variations (1–2 km) as observed from the radiosondes. However, the ECMWF analysis systematically underestimates the ABL heights. The sharp refractivity gradient at the ABL top frequently exceeds the critical refraction (e.g., −157 N-unit km−1) and becomes the so-called ducting condition, which results in a systematic RO refractivity bias (or called N-bias) inside the ABL. Simulation study based on radiosonde profiles reveals the magnitudes of the N-biases are vertical resolution dependent. The $N$-bias is also the primary cause of the systematically smaller refractivity gradient (rarely exceeding −110 N-unit km−1) at the ABL top from RO measurement. However, the N-bias seems not affect the ABL height detection. Instead, the very large RO bending angle and the sharp refractivity gradient due to ducting allow reliable detection of the ABL height from GPS RO. The seasonal mean climatology of ABL heights derived from a nine-month composite of COSMIC RO soundings over the SE Pacific reveals significant differences from the ECMWF analysis. Both show an increase of ABL height from the shallow stratocumulus near the coast to a much higher trade wind inversion further off the coast. However, COSMIC RO shows an overall deeper ABL and reveals different locations of the minimum and maximum ABL heights as compared to the ECMWF analysis. At low latitudes, despite the decreasing number of COSMIC RO soundings and the lower percentage of soundings that penetrate into the lowest 500-m above the mean-sea-level, there are small sampling errors in the mean ABL height climatology. The difference of ABL height climatology between COSMIC RO and ECMWF analysis over SE Pacific is significant and requires further studies.

scholarly journals Advances and limitations of atmospheric boundary layer observations with GPS occultation over Southeast Pacific Ocean

2011 ◽  
Vol 11 (8) ◽  
pp. 22857-22891
Author(s):  
F. Xie ◽  
D. L. Wu ◽  
C. O. Ao ◽  
A. J. Mannucci ◽  
E. R. Kursinski
Keyword(s):  
Boundary Layer ◽  
Pacific Ocean ◽  
Atmospheric Boundary Layer ◽  
Temperature Inversion ◽  
Lower Percentage ◽  
Trade Wind ◽  
Sampling Errors ◽  
Wide Range ◽  
The Mean ◽  
The Difference

Abstract. The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific Ocean is featured with a strong temperature inversion and a sharp moisture gradient across the ABL top. The strong moisture and temperature gradients result in a sharp refractivity gradient that can be precisely detected by the Global Positioning System (GPS) radio occultation (RO) measurements. In this paper, the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect a wide range of ABL height variations (1–2 km) as observed from the radiosondes. Whereas, the ECMWF analyses systematically underestimate ABL heights. The sharp refractivity gradient at the ABL top frequently exceeds the critical refraction (e.g., −157 N-unit km−1) and becomes the so-called ducting condition, which results in systematic RO refractivity bias (or called N-bias) inside the ABL. Simulation study using refractivity profiles based on radiosondes reveals that the N-biases are significant and the magnitudes of biases are vertical resolution dependent. The N-bias is also the primary cause of the systematically smaller refractivity gradient (rarely exceeding −110 N-unit km−1) at the ABL top from RO measurement. However, the N-bias seems not affect the ABL height detection. Instead, the very sharp refractivity gradient and the large RO bending angle due to ducting allow reliable detection of ABL height from GPS RO. The seasonal mean climatology of ABL heights derived from a nine-month composite of COSMIC RO soundings over the SE Pacific reveals significant differences from the ECMWF analysis. Both show the deepening of ABL height from the shallow stratocumulus near the coast to a much higher trade wind inversion further off the coast. However, COSMIC RO shows systematically higher ABL heights overall and reveals different locations of the minimum and maximum ABL heights as compared to the ECMWF analysis. The significantly decreasing number of COSMIC RO soundings at lower latitudes along with the lower percentage of RO soundings penetrating into the lowest 500 m above mean-sea-level (a.m.s.l.), result in generally small sampling errors in the mean ABL climatology and will not affect the morphology of RO ABL height climatology. The difference of ABL height climatology between COSMIC RO and ECMWF analysis over SE Pacific is significant and requires further studies.

Helicity in the Ekman boundary layer

2014 ◽  
Vol 755 ◽  
pp. 654-671 ◽  
Author(s):  
Enrico Deusebio ◽  
Erik Lindborg
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Ekman Layer ◽  
Mean Flow ◽  
Left Handed ◽  
Ekman Boundary Layer ◽  
Taylor’S Hypothesis ◽  
Wide Range ◽  
The Mean ◽  
Turbulent Helicity

AbstractHelicity, which is defined as the scalar product of velocity and vorticity, $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\mathcal{H}} = {\boldsymbol {u}} \boldsymbol {\cdot }\boldsymbol{\omega}$, is an inviscidly conserved quantity in a barotropic fluid. Mean helicity is zero in flows that are parity invariant. System rotation breaks parity invariance and has therefore the potential of giving rise to non-zero mean helicity. In this paper we study the helicity dynamics in the incompressible Ekman boundary layer. Evolution equations for the mean field helicity and the mean turbulent helicity are derived and it is shown that pressure flux injects helicity at a rate $ 2 \varOmega G^2 $ over the total depth of the Ekman layer, where $ G $ is the geostrophic wind far from the wall and $ {\boldsymbol{\Omega}} = \varOmega {\boldsymbol {e}}_y $ is the rotation vector and $ {\boldsymbol {e}}_y $ is the wall-normal unit vector. Thus right-handed/left-handed helicity will be injected if $ \varOmega $ is positive/negative. We also show that in the uppermost part of the boundary layer there is a net helicity injection with opposite sign as compared with the totally integrated injection. Isotropic relations for the helicity dissipation and the helicity spectrum are derived and it is shown that it is sufficient to measure two transverse velocity components and use Taylor’s hypothesis in the mean flow direction in order to measure the isotropic helicity spectrum. We compare the theoretical predictions with a direct numerical simulation of an Ekman boundary layer and confirm that there is a preference for right-handed helicity in the lower part of the Ekman layer and left-handed helicity in the uppermost part when $ \varOmega > 0 $. In the logarithmic range, the helicity dissipation conforms to isotropic relations. On the other hand, spectra show significant departures from isotropic conditions, suggesting that the Reynolds number considered in the study is not sufficiently large for isotropy to be valid in a wide range of scales. Our analytical and numerical results strongly suggest that there is a turbulent helicity cascade of right-handed helicity in the logarithmic range of the atmospheric boundary layer when $\varOmega >0$, consistent with recent measurements by Koprov, Koprov, Ponomarev & Chkhetiani (Dokl. Phys., vol. 50, 2005, pp. 419–422). The isotropic relations which are derived may facilitate future measurements of the helicity spectrum in the atmospheric boundary layer as well as in controlled wind tunnel experiments.

scholarly journals Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

2017 ◽  
Vol 17 (1) ◽  
pp. 531-549 ◽  
Author(s):  
Sanjay Kumar Mehta ◽  
Madineni Venkat Ratnam ◽  
Sukumarapillai V. Sunilkumar ◽  
Daggumati Narayana Rao ◽  
Boddapaty V. Krishna Murthy
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Diurnal Variation ◽  
Indian Monsoon ◽  
Winter Season ◽  
Monsoon Region ◽  
Diurnal Variability ◽  
The Mean ◽  
Indian Monsoon Region ◽  
Tropical Station

Abstract. The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.

Optimal energy growth in stably stratified turbulent Couette flow

2021 ◽  
Author(s):  
Grigory Zasko ◽  
Andrey Glazunov ◽  
Evgeny Mortikov ◽  
Yuri Nechepurenko ◽  
Pavel Perezhogin
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Couette Flow ◽  
Large Scale ◽  
Thin Layers ◽  
Plane Couette Flow ◽  
Turbulent Layer ◽  
Wide Range ◽  
The Mean ◽  
Optimal Disturbances

<p>In this report, we will try to explain the emergence of large-scale organized structures in stably stratified turbulent flows using optimal disturbances of the mean turbulent flow. These structures have been recently obtained in numerical simulations of turbulent stably stratified flows [1] (Ekman layer, LES) and [2] (plane Couette flow, DNS and LES) and indirectly confirmed by field measurements in the stable boundary layer of the atmosphere [1, 2]. In instantaneous temperature fields they manifest themselves as irregular inclined thin layers with large gradients (fronts), spaced from each other by distances comparable to the height of the entire turbulent layer, and separated by regions with weak stratification.</p><p>Optimal disturbances of a stably stratified turbulent plane Couette flow are investigated in a wide range of Reynolds and Richardson numbers. These disturbances were computed based on a simplified linearized system of equations in which turbulent Reynolds stresses and heat fluxes were approximated by isotropic viscosity and diffusion with coefficients obtained from DNS results. It was shown [3] that the spatial scales and configurations of the inclined structures extracted from DNS data coincide with the ones obtained from optimal disturbances of the mean turbulent flow.</p><p>Critical value of the stability parameter is found starting from which the optimal disturbances resemble inclined structures. The physical mechanisms that determine the evolution, energetics and spatial configuration of these optimal disturbances are discussed. The effects due to the presence of stable stratification are highlighted.</p><p>Numerical experiments with optimal disturbances were supported by the RSF (grant No. 17-71-20149). Direct numerical simulation of stratified turbulent Couette flow was supported by the RFBR (grant No. 20-05-00776).</p><p>References:</p><p>[1] P.P. Sullivan, J.C. Weil, E.G. Patton, H.J. Jonker, D.V. Mironov. Turbulent winds and temperature fronts in large-eddy simulations of the stable atmospheric boundary layer // J. Atmos. Sci., 2016, V. 73, P. 1815-1840.</p><p>[2] A.V. Glazunov, E.V. Mortikov, K.V. Barskov, E.V. Kadantsev, S.S. Zilitinkevich. Layered structure of stably stratified turbulent shear flows // Izv. Atmos. Ocean. Phys., 2019, V. 55, P. 312–323.</p><p>[3] G.V. Zasko, A.V. Glazunov, E.V. Mortikov, Yu.M. Nechepurenko. Large-scale structures in stratified turbulent Couette flow and optimal disturbances // Russ. J. Num. Anal. Math. Model., 2010, V. 35, P. 35–53.</p>

Diagnosing Monthly Mean Boundary Layer Properties from Reanalysis Data Using a Bulk Boundary Layer Model

2006 ◽  
Vol 63 (3) ◽  
pp. 998-1012 ◽  
Author(s):  
Maike Ahlgrimm ◽  
David A. Randall
Keyword(s):  
Boundary Layer ◽  
Pacific Ocean ◽  
Latent Heat ◽  
Reanalysis Data ◽  
Heat Fluxes ◽  
South Pacific Convergence Zone ◽  
Trade Wind ◽  
Layer Model ◽  
The West ◽  
Boundary Layer Model

Abstract The mixed-layer approach to modeling the planetary boundary layer (PBL) is particularly well suited to inversion-topped PBLs, such as the stratocumulus-topped boundary layer found off the west coast of America in the subtropical Pacific Ocean at northern and southern latitudes. However, a strong temperature inversion near 850 hPa (the trade wind inversion) is not confined to the stratocumulus regimes, but has been observed over most parts of the subtropical–tropical Pacific Ocean. In this paper, the authors test the ability of a simple bulk boundary layer model (BBLM) to diagnose entrainment velocity, cumulus mass flux, and surface latent heat flux from monthly mean reanalysis data. The PBL depth is estimated from Geoscience Laser Altimeter System data. The model is based on the conservation equations for mass, total water mixing ratio, and moist static energy. The BBLM diagnoses entrainment velocities between 1 and 8 mm s−1 in the stratocumulus and trade wind regions, with increasing rates toward the west. Large cumulus mass fluxes (1.3–2 cm s−1) mark the ITCZ and South Pacific convergence zone. Unreasonably large surface latent heat fluxes are diagnosed in regions where the vertical resolution of both model and input data are insufficient to represent the sharp gradients of moist conservable variables and winds across the PBL top. The results demonstrate that the potential exists to extract useful information about the large-scale structure of PBL physical processes by combining available observations with simple models.

scholarly journals Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

2004 ◽  
Vol 22 (8) ◽  
pp. 2679-2691 ◽  
Author(s):  
M. V. Ramana ◽  
P. Krishnan ◽  
S. Muraleedharan Nair ◽  
P. K. Kunhikrishnan
Keyword(s):  
Boundary Layer ◽  
Indian Ocean ◽  
Atmospheric Boundary Layer ◽  
Mixed Layer ◽  
Arabian Sea ◽  
Trade Wind ◽  
Back Trajectory ◽  
Spatial And Temporal Variability ◽  
Air Mass ◽  
The Indian Ocean

Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.

The flat plate boundary layer. Part 1. Numerical integration of the Orr–-Sommerfeld equation

1970 ◽  
Vol 43 (4) ◽  
pp. 801-811 ◽  
Author(s):  
R. Jordinson
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Plate Boundary ◽  
Mean Flow ◽  
Comparison With Experiment ◽  
Wide Range ◽  
The Mean ◽  
Sommerfeld Equation ◽  
Range Of Values ◽  
Flat Plate Boundary Layer

Numerical space-amplified solutions of the Orr-Sommerfeld equation for the case of a boundary layer on a flat plate have been calculated for a wide range of values of frequency and Reynolds number. The mean flow is assumed to be parallel and given by the appropriate component of the Blasius solution. The results are presented in a form suitable for comparison with experiment and are also compared with calculations of earlier authors.

scholarly journals Response Variability in Balanced Cortical Networks

2006 ◽  
Vol 18 (3) ◽  
pp. 634-659 ◽  
Author(s):  
Alexander Lerchner ◽  
Cristina Ursta ◽  
John Hertz ◽  
Mandana Ahmadi ◽  
Pauline Ruffiot ◽  
...  
Keyword(s):  
Mean Field ◽  
Excitatory Input ◽  
Response Variability ◽  
Cortical Column ◽  
Single Model ◽  
Wide Range ◽  
High Connectivity ◽  
The Mean ◽  
The Difference ◽  
External Population

We study the spike statistics of neurons in a network with dynamically balanced excitation and inhibition. Our model, intended to represent a generic cortical column, comprises randomly connected excitatory and inhibitory leaky integrate-and-fire neurons, driven by excitatory input from an external population. The high connectivity permits a mean field description in which synaptic currents can be treated as gaussian noise, the mean and autocorrelation function of which are calculated self-consistently from the firing statistics of single model neurons. Within this description, a wide range of Fano factors is possible. We find that the irregularity of spike trains is controlled mainly by the strength of the synapses relative to the difference between the firing threshold and the postfiring reset level of the membrane potential. For moderately strong synapses, we find spike statistics very similar to those observed in primary visual cortex.

scholarly journals Evaluation of Polar WRF from Modeling the Atmospheric Boundary Layer over Antarctic Sea Ice in Autumn and Winter

2012 ◽  
Vol 140 (12) ◽  
pp. 3919-3935 ◽  
Author(s):  
Esa-Matti Tastula ◽  
Timo Vihma ◽  
Edgar L Andreas
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Surface Temperature ◽  
Atmospheric Boundary Layer ◽  
Inversion Layer ◽  
Temperature Inversion ◽  
Heat Fluxes ◽  
Poor Correlation ◽  
Antarctic Sea Ice ◽  
Autumn And Winter

Abstract Regional simulations of the atmospheric boundary layer over Antarctic sea ice that have been adequately validated are rare. To address this gap, the authors use the doubly nested Polar Weather Research and Forecasting (Polar WRF) mesoscale model to simulate conditions during Ice Station Weddell (ISW) in the austral autumn and winter of 1992. The WRF simulations test two boundary layer schemes: Mellor–Yamada–Janjic and the Asymmetric Convective Model. Validation is against surface-layer and sounding observations from ISW. Simulated latent and sensible heat fluxes for both boundary layer schemes had poor correlation with the observed fluxes. Simulated surface temperature had better correlation with the observations, with a typical bias of 0–2 K and a root-mean-square error of 6–7 K. For surface temperature and wind speed, the Polar WRF yielded better results than the ECMWF Re-Analysis Interim (ERA-Interim). A more challenging test of the simulations is to reproduce features of the low-level jet and the temperature inversion, which were observed, respectively, in 80% and 96% of the ISW radiosoundings. Both boundary layer schemes produce only about half as many jets as were observed. Moreover, the simulated jet coincided with an observed jet only about 30% of the time. The number of temperature inversions and the height at the inversion base were better reproduced, although this was not the case with the depth of the inversion layer. Simulations of the temperature inversion improved when forecasts of cloud fraction agreed to within 0.3 with observations. The modeled inversions were strongest when the incoming longwave radiation was smallest, but this relationship was not observed at ISW.

Structure functions of turbulence in the atmospheric boundary layer over the ocean

1970 ◽  
Vol 44 (1) ◽  
pp. 145-159 ◽  
Author(s):  
C. W. Van Atta ◽  
W. Y. Chen
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Fourth Order ◽  
Structure Functions ◽  
Inertial Subrange ◽  
Order Structure ◽  
Third Order ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Order Quantities

Structure functions of turbulent velocity fluctuations up to fourth order have been measured at several heights in the atmospheric boundary layer over the open ocean, and the results are compared with theoretical predictions for separations in the inertial subrange. The behaviour of second- and third-order quantities shows substantial agreement with the predictions of Kolmogorov's original theory over a wide range of separations, but the results of a recent modification of the theory, attempting to account for intermittency in the local dissipation rate, are also consistent with the data over somewhat shorter separation intervals. The behaviour of the measured fourth-order structure function disagrees with that predicted from Kolmogorov's original work, but good agreement is found with the results of the modified theory.

Sign in / Sign up

Export Citation Format

Share Document