scholarly journals On Air–Sea Interaction at the Mouth of the Gulf of California

2007 ◽  
Vol 20 (9) ◽  
pp. 1649-1661 ◽  
Author(s):  
Paquita Zuidema ◽  
Chris Fairall ◽  
Leslie M. Hartten ◽  
Jeffrey E. Hare ◽  
Daniel Wolfe
Keyword(s):  
Boundary Layer ◽  
Liquid Phase ◽  
Mixed Layer ◽  
Diurnal Cycle ◽  
Gulf Of California ◽  
Sea Breeze ◽  
Near Surface ◽  
Oceanic Mixed Layer ◽  
The Mean ◽  
Moist Layer

Abstract Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (∼23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experiment-mean findings include a net heat input from the atmosphere into the ocean of 70 W m−2. The dominant cooling was an experiment-mean latent heat flux of 108 W m−2, equivalent to an evaporation rate of 0.16 mm h−1. Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2- and 3-km altitude associated with a land–sea breeze, and a broad moist layer at 5–6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000–700-hPa winds reached 12 m s−1, net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2–3 km and another at 5–6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5–6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States.

scholarly journals Verifying Operational Forecasts of Land–Sea-Breeze and Boundary Layer Mixing Processes

2020 ◽  
Vol 35 (4) ◽  
pp. 1427-1445
Author(s):  
Ewan Short
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Spatial Scales ◽  
Sea Breeze ◽  
Absolute Error ◽  
Wind Fields ◽  
Mixing Processes ◽  
Relative Contribution ◽  
The Mean ◽  
Diurnal Wind

AbstractForecasters working for Australia’s Bureau of Meteorology (BoM) produce a 7-day forecast in two key steps: first they choose a model guidance dataset to base the forecast on, and then they use graphical software to manually edit these data. Two types of edits are commonly made to the wind fields that aim to improve how the influences of boundary layer mixing and land–sea-breeze processes are represented in the forecast. In this study the diurnally varying component of the BoM’s official wind forecast is compared with that of station observations and unedited model guidance datasets. Coastal locations across Australia over June, July, and August 2018 are considered, with data aggregated over three spatial scales. The edited forecast produces a lower mean absolute error than model guidance at the coarsest spatial scale (over 50 000 km2), and achieves lower seasonal biases over all spatial scales. However, the edited forecast only reduces errors or biases at particular times and locations, and rarely produces lower errors or biases than all model guidance products simultaneously. To better understand physical reasons for biases in the mean diurnal wind cycles, modified ellipses are fitted to the seasonally averaged diurnal wind temporal hodographs. Biases in the official forecast diurnal cycle vary with location for multiple reasons, including biases in the directions that sea breezes approach coastlines, amplitude biases, and disagreement in the relative contribution of sea-breeze and boundary layer mixing processes to the mean diurnal cycle.

scholarly journals Diurnal Coupling in the Tropical Oceans of CCSM3

2006 ◽  
Vol 19 (11) ◽  
pp. 2347-2365 ◽  
Author(s):  
Gokhan Danabasoglu ◽  
William G. Large ◽  
Joseph J. Tribbia ◽  
Peter R. Gent ◽  
Bruce P. Briegleb ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Upper Ocean ◽  
Solar Forcing ◽  
Layer Depth ◽  
Climate System Model ◽  
Tropical Oceans ◽  
Ocean Coupling ◽  
Coupling Interval ◽  
The Mean

Abstract New features that may affect the behavior of the upper ocean in the Community Climate System Model version 3 (CCSM3) are described. In particular, the addition of an idealized diurnal cycle of solar forcing where the daily mean solar radiation received in each daily coupling interval is distributed over 12 daylight hours is evaluated. The motivation for this simple diurnal cycle is to improve the behavior of the upper ocean, relative to the constant forcing over each day of previous CCSM versions. Both 1- and 3-h coupling intervals are also considered as possible alternatives that explicitly resolve the diurnal cycle of solar forcing. The most prominent and robust effects of all these diurnal cycles are found in the tropical oceans, especially in the Pacific. Here, the mean equatorial sea surface temperature (SST) is warmed by as much as 1°C, in better agreement with observations, and the mean boundary layer depth is reduced. Simple rectification of the diurnal cycle explains about half of the shallowing, but less than 0.1°C of the warming. The atmospheric response to prescribed warm SST anomalies of about 1°C displays a very different heat flux signature. The implication, yet to be verified, is that large-scale air–sea coupling is a prime mechanism for amplifying the rectified, daily averaged SST signals seen by the atmosphere. Although the use of upper-layer temperature for SST in CCSM3 underestimates the diurnal cycle of SST, many of the essential characteristics of diurnal cycling within the equatorial ocean are reproduced, including boundary layer depth, currents, and the parameterized vertical heat and momentum fluxes associated with deep-cycle turbulence. The conclusion is that the implementation of an idealized diurnal cycle of solar forcing may make more frequent ocean coupling and its computational complications unnecessary as improvements to the air–sea coupling in CCSM3 continue. A caveat here is that more frequent ocean coupling tends to reduce the long-term cooling trends typical of CCSM3 by heating already too warm ocean depths, but longer integrations are needed to determine robust features. A clear result is that the absence of diurnal solar forcing of the ocean has several undesirable consequences in CCSM3, including too large ENSO variability, much too cold Pacific equatorial SST, and no deep-cycle turbulence.

scholarly journals Boundary layer evolution over the central Himalayas from radio wind profiler and model simulations

2016 ◽  
Vol 16 (16) ◽  
pp. 10559-10572 ◽  
Author(s):  
Narendra Singh ◽  
Raman Solanki ◽  
Narendra Ojha ◽  
Ruud H. H. Janssen ◽  
Andrea Pozzer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Surface Ozone ◽  
Wrf Model ◽  
Ground Level ◽  
Wind Profiler ◽  
Pollution Transport ◽  
Local Boundary ◽  
The Mean

Abstract. We investigate the time evolution of the Local Boundary Layer (LBL) for the first time over a mountain ridge at Nainital (79.5° E, 29.4° N, 1958 m a.m.s.l.) in the central Himalayan region, using a radar wind profiler (RWP) during November 2011 to March 2012, as a part of the Ganges Valley Aerosol Experiment (GVAX). We restrict our analysis to clear–sunny days, resulting in a total of 78 days of observations. The standard criterion of the peak in the signal-to-noise ratio (S ∕ N) profile was found to be inadequate in the characterization of mixed layer (ML) top at this site. Therefore, we implemented a criterion of S ∕ N > 6 dB for the characterization of the ML and the resulting estimations are shown to be in agreement with radiosonde measurements over this site. The daytime average (05:00–10:00 UTC) observed boundary layer height ranges from 440 ± 197 m in November (late autumn) to 766 ± 317 m above ground level (a.g.l.) in March (early spring). The observations revealed a pronounced impact of mountain topography on the LBL dynamics during March, when strong winds (> 5.6 m s−1) lead to LBL heights of 650 m during nighttime. The measurements are further utilized to evaluate simulations from the Weather Research and Forecasting (WRF) model. WRF simulations captured the day-to-day variations up to an extent (r2 = 0.5), as well as the mean diurnal variations (within 1σ variability). The mean biases in the daytime average LBL height vary from −7 % (January) to +30 % (February) between model and observations, except during March (+76 %). Sensitivity simulations using a mixed layer model (MXL/MESSy) indicated that the springtime overestimation of LBL would lead to a minor uncertainty in simulated surface ozone concentrations. However, it would lead to a significant overestimation of the dilution of black carbon aerosols at this site. Our work fills a gap in observations of local boundary layer over this complex terrain in the Himalayas, and highlights the need for year-long simultaneous measurements of boundary layer dynamics and air quality to better understand the role of lower tropospheric dynamics in pollution transport.

Diurnal and Seasonal Lightning Variability over the Gulf Stream and the Gulf of Mexico

2015 ◽  
Vol 72 (7) ◽  
pp. 2657-2665 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace ◽  
Michael L. Hutchins ◽  
Robert H. Holzworth
Keyword(s):  
Gulf Of Mexico ◽  
Diurnal Cycle ◽  
Gulf Stream ◽  
Land Surface ◽  
Southeastern United States ◽  
Surface Wind ◽  
Tropical Rainfall Measuring Mission ◽  
Sea Breeze ◽  
Near Surface ◽  
Early Evening

Recent observations from the World Wide Lightning Location Network (WWLLN) reveal a pronounced lightning maximum over the warm waters of the Gulf Stream that exhibits distinct diurnal and seasonal variability. Lightning is most frequent during summer (June–August). During afternoon and early evening, lightning is enhanced just onshore of the coast of the southeastern United States because of daytime heating of the land surface and the resulting sea-breeze circulations and convection. Near-surface wind observations from the Quick Scatterometer (QuikSCAT) satellite indicate divergence over the Gulf of Mexico and portions of the Gulf Stream at 1800 LT, at which time lightning activity is suppressed there. Lightning frequency exhibits a broad maximum over the Gulf Stream from evening through noon of the following day, and QuikSCAT wind observations at 0600 LT indicate low-level winds blowing away from the continent and converging over the Gulf Stream. Over the northern Gulf of Mexico, lightning is most frequent from around sunrise through late morning. During winter, lightning exhibits a weak diurnal cycle over the Gulf Stream, with most frequent lightning during the evening. Precipitation rates from a 3-hourly gridded dataset that incorporates observations from Tropical Rainfall Measuring Mission (TRMM), as well as other satellites, exhibit a diurnal cycle over the Gulf Stream that lags the lightning diurnal cycle by several hours.

scholarly journals An observational study of the evolution of the atmospheric boundary-layer over Cabo Frio, Brazil

2007 ◽  
Vol 25 (8) ◽  
pp. 1735-1744 ◽  
Author(s):  
S. H. Franchito ◽  
V. Brahmananda Rao ◽  
T. O. Oda ◽  
J. C. Conforte
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Mixed Layer ◽  
Coastal Upwelling ◽  
Vertical Mixing ◽  
Austral Summer ◽  
Sea Breeze ◽  
Austral Winter ◽  
Atmospheric Mixed Layer ◽  
Cabo Frio

Abstract. The effect of coastal upwelling on the evolution of the atmospheric boundary layer (ABL) in Cabo Frio (Brazil) is investigated. For this purpose, radiosounding data collected in two experiments made during the austral summer (upwelling case) and austral winter (no upwelling case) are analysed. The results show that during the austral summer, cold waters that crop up near the Cabo Frio coast favour the formation of an atmospheric stable layer, which persists during the upwelling episode. Due to the low SSTs, the descending branch of the sea-breeze circulation is located close to the coast, inhibiting the development of a mixed layer mainly during the day. At night, with the reduction of the land-sea thermal contrast the descending motion is weaker, allowing a vertical mixing. The stable ABL favours the formation of a low level jet, which may also contribute to the development of a nocturnal atmospheric mixed layer. During the austral winter, due to the higher SSTs observed near the coast, the ABL is less stable compared with that in the austral summer. Due to warming, a mixed layer is observed during the day. The observed vertical profiles of the zonal winds show that the easterlies at low levels are stronger in the austral summer, indicating that the upwelling modulates the sea-breeze signal, thus confirming model simulations.

scholarly journals Parameterization of convective transport in the boundary layer and its impact on the representation of the diurnal cycle of wind and dust emissions

2015 ◽  
Vol 15 (12) ◽  
pp. 6775-6788 ◽  
Author(s):  
F. Hourdin ◽  
M. Gueye ◽  
B. Diallo ◽  
J.-L. Dufresne ◽  
J. Escribano ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
General Circulation ◽  
Surface Wind ◽  
Circulation Model ◽  
Convective Transport ◽  
Strong Nonlinearity ◽  
Thermal Plumes ◽  
Near Surface ◽  
Dust Emissions

Abstract. We investigate how the representation of the boundary layer in a climate model impacts the representation of the near-surface wind and dust emission, with a focus on the Sahel/Sahara region. We show that the combination of vertical turbulent diffusion with a representation of the thermal cells of the convective boundary layer by a mass flux scheme leads to realistic representation of the diurnal cycle of wind in spring, with a maximum near-surface wind in the morning. This maximum occurs when the thermal plumes reach the low-level jet that forms during the night at a few hundred meters above surface. The horizontal momentum in the jet is transported downward to the surface by compensating subsidence around thermal plumes in typically less than 1 h. This leads to a rapid increase of wind speed at surface and therefore of dust emissions owing to the strong nonlinearity of emission laws. The numerical experiments are performed with a zoomed and nudged configuration of the LMDZ general circulation model coupled to the emission module of the CHIMERE chemistry transport model, in which winds are relaxed toward that of the ERA-Interim reanalyses. The new set of parameterizations leads to a strong improvement of the representation of the diurnal cycle of wind when compared to a previous version of LMDZ as well as to the reanalyses used for nudging themselves. It also generates dust emissions in better agreement with current estimates, but the aerosol optical thickness is still significantly underestimated.

scholarly journals Forecasting global atmospheric CO<sub>2</sub>

2014 ◽  
Vol 14 (9) ◽  
pp. 13909-13962 ◽  
Author(s):  
A. Agustí-Panareda ◽  
S. Massart ◽  
F. Chevallier ◽  
S. Boussetta ◽  
G. Balsamo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Real Time ◽  
Diurnal Cycle ◽  
Spatial Scales ◽  
Weather Prediction ◽  
Physical Models ◽  
Atmospheric Co2 ◽  
Co2 Fluxes ◽  
Near Surface ◽  
Forecasting System

Abstract. A new global atmospheric carbon dioxide (CO2) real-time forecast is now available as part of the pre-operational Monitoring of Atmospheric Composition and Climate – Interim Implementation (MACC-II) service using the infrastructure of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). One of the strengths of the CO2 forecasting system is that the land surface, including vegetation CO2 fluxes, is modelled online within the IFS. Other CO2 fluxes are prescribed from inventories and from off-line statistical and physical models. The CO2 forecast also benefits from the transport modelling from a state-of-the-art numerical weather prediction (NWP) system initialized daily with a wealth of meteorological observations. This paper describes the capability of the forecast in modelling the variability of CO2 on different temporal and spatial scales compared to observations. The modulation of the amplitude of the CO2 diurnal cycle by near-surface winds and boundary layer height is generally well represented in the forecast. The CO2 forecast also has high skill in simulating day-to-day synoptic variability. In the atmospheric boundary layer, this skill is significantly enhanced by modelling the day-to-day variability of the CO2 fluxes from vegetation compared to using equivalent monthly mean fluxes with a diurnal cycle. However, biases in the modelled CO2 fluxes also lead to accumulating errors in the CO2 forecast. These biases vary with season with an underestimation of the amplitude of the seasonal cycle both for the CO2 fluxes compared to total optimized fluxes and the atmospheric CO2 compared to observations. The largest biases in the atmospheric CO2 forecast are found in spring, corresponding to the onset of the growing season in the Northern Hemisphere. In the future, the forecast will be re-initialized regularly with atmospheric CO2 analyses based on the assimilation of CO2 satellite retrievals, as they become available in near-real time. In this way, the accumulation of errors in the atmospheric CO2 forecast will be reduced. Improvements in the CO2 forecast are also expected with the continuous developments in the operational IFS.

scholarly journals Parameterizations of Sea-Spray Impact on the Air–Sea Momentum and Heat Fluxes

2011 ◽  
Vol 139 (12) ◽  
pp. 3781-3797 ◽  
Author(s):  
J.-W. Bao ◽  
C. W. Fairall ◽  
S. A. Michelson ◽  
L. Bianco
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Weather Prediction ◽  
Heat Fluxes ◽  
Sea Spray ◽  
Surface Boundary ◽  
Near Surface ◽  
The Mean ◽  
Momentum And Heat Fluxes ◽  
The Impact

Abstract This paper focuses on parameterizing the effect of sea spray at hurricane-strength winds on the momentum and heat fluxes in weather prediction models using the Monin–Obukhov similarity theory (a common framework for the parameterizations of air–sea fluxes). In this scheme, the mass-density effect of sea spray is considered as an additional modification to the stratification of the near-surface profiles of wind, temperature, and moisture in the marine surface boundary layer (MSBL). The overall impact of sea-spray droplets on the mean profiles of wind, temperature, and moisture depends on the wind speed at the level of sea-spray generation. As the wind speed increases, the mean droplet size and the mass flux of sea-spray increase, rendering an increase of stability in the MSBL and the leveling-off of the surface drag. Sea spray also tends to increase the total air–sea sensible and latent heat fluxes at high winds. Results from sensitivity testing of the scheme in a numerical weather prediction model for an idealized case of hurricane intensification are presented along with a dynamical interpretation of the impact of the parameterized sea-spray physics on the structure of the hurricane boundary layer.

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