Assessment of the Uncertainties in Arctic Low-Level Temperature Inversion Characteristics in Radio Occultation Observations

2017 ◽  
Vol 55 (3) ◽  
pp. 1793-1803 ◽  
Author(s):  
Liang Chang ◽  
Shuli Song ◽  
Guiping Feng ◽  
Yang Zhang ◽  
Guoping Gao
Keyword(s):  
Radio Occultation ◽  
Temperature Inversion ◽  
Low Level

scholarly journals Orographic Drag Associated with Lee Waves Trapped at an Inversion

2013 ◽  
Vol 70 (9) ◽  
pp. 2930-2947 ◽  
Author(s):  
Miguel A. C. Teixeira ◽  
José Luis Argaín ◽  
Pedro M. A. Miranda
Keyword(s):  
Numerical Simulations ◽  
Mixed Boundary ◽  
Single Layer ◽  
Temperature Inversion ◽  
Static Stability ◽  
Wave Drag ◽  
Low Level ◽  
Flow Parameters ◽  
Lee Waves ◽  
Lee Wave

Abstract The drag produced by 2D orographic gravity waves trapped at a temperature inversion and waves propagating in the stably stratified layer existing above are explicitly calculated using linear theory, for a two-layer atmosphere with neutral static stability near the surface, mimicking a well-mixed boundary layer. For realistic values of the flow parameters, trapped-lee-wave drag, which is given by a closed analytical expression, is comparable to propagating-wave drag, especially in moderately to strongly nonhydrostatic conditions. In resonant flow, both drag components substantially exceed the single-layer hydrostatic drag estimate used in most parameterization schemes. Both drag components are optimally amplified for a relatively low-level inversion and Froude numbers Fr ≈ 1. While propagating-wave drag is maximized for approximately hydrostatic flow, trapped-lee-wave drag is maximized for l2a = O(1) (where l2 is the Scorer parameter in the stable layer and a is the mountain width). This roughly happens when the horizontal scale of trapped lee waves matches that of the mountain slope. The drag behavior as a function of Fr for l2H = 0.5 (where H is the inversion height) and different values of l2a shows good agreement with numerical simulations. Regions of parameter space with high trapped-lee-wave drag correlate reasonably well with those where lee-wave rotors were found to occur in previous nonlinear numerical simulations including frictional effects. This suggests that trapped-lee-wave drag, besides giving a relevant contribution to low-level drag exerted on the atmosphere, may also be useful to diagnose lee-rotor formation.

scholarly journals Low-level jet characteristics over the Arctic Ocean in spring and summer

2013 ◽  
Vol 13 (1) ◽  
pp. 2125-2153
Author(s):  
L. Jakobson ◽  
T. Vihma ◽  
E. Jakobson ◽  
T. Palo ◽  
A. Männik ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Temperature Inversion ◽  
The Arctic ◽  
Jet Streams ◽  
Central Arctic Ocean ◽  
Turbulent Layer ◽  
Low Level ◽  
Low Level Jet ◽  
Jet Characteristics

Abstract. Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the bases of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46%) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationship between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated to transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations, gusts, and fronts were detected. In approximately 50% of the observed LLJs the generation mechanism remained unclear, but in most of these cases the wind speed was strong in the whole vertical profile, the jet core representing only a weak maximum. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.

A Procedure For Studying Mountain Effects at Low Levels

1954 ◽  
Vol 35 (9) ◽  
pp. 412-416 ◽  
Author(s):  
Uwe Radok
Keyword(s):  
Temperature Inversion ◽  
Point Of View ◽  
Air Pressure ◽  
The Other ◽  
Lapse Rate ◽  
Temperature Lapse Rate ◽  
Low Level ◽  
Lee Waves ◽  
Low Levels ◽  
Mountainous Country

A representative picture, from the aeronautical point of view, of vertical currents above mountainous country is obtained by letting these currents act on an aircraft set to fly horizontally in still air. Pressure and temperature traces recorded by such an aircraft give the effective vertical velocities and some idea of the temperature lapse rate in the undisturbed stream. Two sets of results are given for illustration. One shows low-level lee waves which were caused presumably by a temperature inversion; the other is a case of strong turbulence side by side with a smooth wave, in which downdrafts reached 1600 ft/min in an 18-knot wind.

scholarly journals The Low-Level Atmospheric Circulation near Tongoy Bay–Point Lengua de Vaca (Chilean Coast, 30°S)

2011 ◽  
Vol 139 (11) ◽  
pp. 3628-3647 ◽  
Author(s):  
David A. Rahn ◽  
René D. Garreaud ◽  
José A. Rutllant
Keyword(s):  
Boundary Layer ◽  
Ocean Circulation ◽  
Sea Breeze ◽  
Temperature Inversion ◽  
High Elevation ◽  
Marine Terrace ◽  
Offshore Structure ◽  
Local Circulation ◽  
Wind Maximum ◽  
Low Level

Abstract Strong southerly, terrain parallel winds often occur along the coast of north-central Chile (25°–35°S) embedded in the marine atmospheric boundary layer and the lower part of the capping temperature inversion. Their offshore structure and variability have received considerable attention because of the effect on open-ocean processes and connection with the southeast Pacific cloud layer. Mesoscale low-level circulations linked to the coastal topography (e.g., coastal jets and sea breeze) are less studied in Chile, but are particularly relevant as they alter the upper-ocean circulation and the cloud pattern in the nearshore strip. Surface, radiosonde, and airborne meteorological observations near point Lengua de Vaca (LdV)–Tongoy Bay (TB) at 30°S are used alongside numerical modeling to understand the local circulation near a prominent upwelling center. Most observations were gathered during the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Chilean Upwelling Experiment (VOCALS-CUpEx) during two weeks in late spring 2009. The regional topography resembles other major capes, but south of TB and east of LdV there is a low (100–300 m), dry marine terrace bounded by high elevation at the coast (~600 m) and farther inland. Coastal soundings 25 km upstream of LdV revealed a southerly wind maximum near the surface and another at 900 m separated by a destabilized layer, deviating from the two-layer model often applied to coastal flow. In the morning a shallow sea breeze penetrates from TB to the marine terrace, but is overridden by southerly flow in the afternoon. Furthermore, between 400 and 900 m, warm continental air is advected from over the marine terrace creating a residual boundary layer over TB. Concurrent with slower changes offshore, the low-level warming over TB leads to a marked cross-shore pressure gradient enhancing the coastal jet just north of LdV.

scholarly journals The Coastal Boundary Layer at the Eastern Margin of the Southeast Pacific (23.4°S, 70.4°W): Cloudiness-Conditioned Climatology

2011 ◽  
Vol 24 (4) ◽  
pp. 1013-1033 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
Rosa A. Zamora ◽  
José A. Rutllant
Keyword(s):  
Boundary Layer ◽  
Lower Troposphere ◽  
Temperature Inversion ◽  
Austral Winter ◽  
Radiative Balance ◽  
Low Level ◽  
Southeast Pacific ◽  
Coastal Margin ◽  
Coastal Boundary Layer ◽  
Coastal Boundary

Abstract A basic climatological description of 29 years of surface and upper-air observations at a coastal site (23.4°S, 70.4°W) in northern Chile is presented. The site is considered to be generally representative of the eastern coastal margin of the southeast Pacific stratocumulus region, which plays an important role in the global radiative balance. The analysis focuses on two of the main elements affecting coastal weather in this region: low-level cloudiness and the state of the subsidence temperature inversion. The objectives of the paper are 1) to present the basic climatological features of these elements and 2) to document the differences in the structure of this coastal boundary layer (BL) associated with the presence or absence of low-level clouds. Low-level clouds (defined here as ceilings less than 1500 m AGL) occur at the site mostly in the night, especially during austral winter and spring. Elevated subsidence inversions show a very large prevalence in the 1200 UTC [0800 local time (LT)] radiosonde profiles analyzed here, with base heights typically between 800 and 1100 m. The seasonal cycle of the subsidence inversion shows an ∼300-m amplitude at inversion base and top and a substantial BL cooling in austral winter. Generally weak and shallow surface-based inversions at 1200 UTC (0800 LT) are present in about 15% of the soundings, with more frequent occurrence in austral fall. The second objective was accomplished by compositing surface meteorology and upper-air profiles conditioned by nighttime low-level cloudiness. More frequent surface inversions in temperature and dewpoint are found for mostly clear nights, as compared to mostly cloudy nighttime conditions. The clear-night BL shows a more stable temperature profile and larger vertical gradients in mixing ratio when compared to the approximately well-mixed cloud-topped BL. Above the BL, the clear composites show a weaker subsidence inversion and more intense northerly winds in the 1000–3000-m layer compared to the cloudy cases. Insights into the physical mechanisms underlying the findings above were sought by comparing the cloudy composites to results of a stationary mixed-layer model of a stratus-capped marine BL, by computing derived parameters pertaining to the temperature budget and the turbulent state of the lower troposphere and by using reanalysis fields to compute regional circulation anomalies associated to coastal low-level cloudiness. The results show physically significant differences in subsidence, horizontal temperature advection, and winds in the lower troposphere associated with the mean clear and cloudy coastal BL. Coastal clear nights appear associated with a cold anomaly in the lower troposphere over the southeast Pacific basin offshore of Peru and Chile, which by thermal wind arguments induce anomalies of southerly winds along the Chilean coast near the surface and northerly winds above the BL, while at the same time reducing the coastal subsidence in the lower troposphere. These results point to the importance of properly representing the sea–land temperature contrast and the topographic impact on the lower-tropospheric flow in order to adequately model the coastal BL mean state over this region.

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