The influence of the large-scale circulation on the thermodynamic profiles in the trades from a Lagrangian perspective

2020 ◽  
Author(s):  
Leonie Villiger ◽  
Franziska Aemisegger ◽  
Maxi Boettcher ◽  
Heini Wernli
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Cloud Amount ◽  
Phase Changes ◽  
Stable Water Isotopes ◽  
Geophysical Research ◽  
Large Scale Circulation ◽  
Near Surface ◽  
Diabatic Processes ◽  
The Impact

<p>In the tropical winter trades of the North Atlantic in the vicinity of Barbados four different mesoscale organisation patterns of clouds – sugar, gravel, flower, fish - are observed regularly. Each pattern is associated with a distinct cloud amount and radiative footprint. Therefore, the relative occurrence frequency of these patterns affects the global radiative budget. As shown by a recent study (Bony et al. 2019, Geophysical Research Letter), the occurrence of the four patterns is controlled by the near-surface wind speed and the strength of lower tropospheric instability. It is however not yet clear, whether these cloud patterns occur preferably in specific larger-scale flow configurations. These can be associated for example with upper-level wave breaking in the extratropics and different positions and strengths of low-level subtropical anticyclones.</p><p>Lower tropospheric air parcels at different altitudes in the trades are expected to have different transport histories associated with distinct diabatic processes such as radiative effects, phase changes within and below clouds and turbulent mixing. The diabatic processes encountered during transport modulate the thermodynamic properties of the air parcels and therefore influence the vertical thermodynamic structure of the atmosphere in the trades.</p><p>In this study, the impact of large-scale air mass advection on the thermodynamic profiles over Barbados is analysed for each of the four mesoscale organisation patterns observed during EUREC4A. The airmass transport history is characterised for different homogenous atmospheric layers. These layers are identified based on vertical pseudo-soundings above the Barbados Cloud Observatory (BCO) using ECMWF analysis data for cases where profiles agree well with independent observations from balloon soundings. The large-scale circulation within the 10 days prior to the sounding is considered for computing the trajectories of the air masses arriving in these layers. Backward trajectories are calculated with three-dimensional analysis wind fields. Thereby, the thermodynamic history and large-scale circulation configuration associated with the four cloud organisation patterns is described from a Lagrangian perspective. In addition, composites of the sea level pressure field provide information whether the four patterns co-occur with systematically differing positions and/or intensities of subtropical anticyclones. In future work, stable water isotopes will be used as observational tracers to find supportive evidence of the characterised transport history.</p>

scholarly journals Wind patterns associated with the development of daytime thunderstorms over Istria

2014 ◽  
Vol 32 (4) ◽  
pp. 401-420 ◽  
Author(s):  
G. Poljak ◽  
M. T. Prtenjak ◽  
M. Kvakić ◽  
N. Strelec Mahović ◽  
K. Babić
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Sea Breeze ◽  
Moist Convection ◽  
Near Surface ◽  
Low Level ◽  
Synoptic Conditions ◽  
Storm Cells ◽  
The Impact ◽  
Wind Patterns

Abstract. The northeastern (NE) Adriatic in the northern Mediterranean is the area with (i) the highest frequency of thunderstorms in Croatia, and (ii) frequent appearances of sea breeze (SB) along the coast. This study investigates the impact of the combined large-scale wind (associated with particular synoptic conditions) and the SB on the moist convection development over the NE Adriatic. The four selected cases were (i) chosen on the basis of a daytime moist convection; (ii) supplemented by one of the dominant large-scale winds with seaward (NE, NW) and landward (SW, SE) directions and (iii) simulated by WRF numerical model. The near-surface wind patterns consisted of SBs along the coastline, generated a narrow eastward-moving convergence zone (CZ) along the area if the large-scale wind was less than 9 m s−1 (below 500 hPa). Apart from the low-level CZ, the advection of large-scale wind influenced the lifetime and movement of the initial Cb cells. While the local front collision with the NE wind advection caused the thunderstorm to propagate southward, the CZ and fronts interaction determined the afternoon northwestward storm movement against the NW large-scale wind. Due to particular synoptic background, the thunderstorm event in SE case was the shortest with only a minor impact on the SB. While the origins and locations of storm cells were completely controlled by the low-level CZ and the upward advection of low-level moisture at the SB front, the most typical convective case with SW warm-wet wind only partially supported the SB–Cb interaction.

scholarly journals Improvements in Typhoon Forecasts with Assimilated GPS Occultation Refractivity

2005 ◽  
Vol 20 (6) ◽  
pp. 931-953 ◽  
Author(s):  
Ching-Yuang Huang ◽  
Ying-Hwa Kuo ◽  
Shu-Hua Chen ◽  
Francois Vandenberghe
Keyword(s):  
Surface Wind ◽  
Mountain Range ◽  
Maximum Magnitude ◽  
Intense Rainfall ◽  
Geophysical Research ◽  
Near Surface ◽  
Accumulated Rainfall ◽  
The Impact ◽  
Mean Square Errors ◽  
Gps Occultation

Abstract In this study, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) with three-dimensional variational data assimilation (3DVAR) is utilized to investigate influences of GPS occultation refractivity on simulations of typhoons past Taiwan. Two recent cases were simulated, including Typhoon Nari in September 2001 and Typhoon Nakri in July 2002. The GPS observation data are taken from the Challenging Minisatellite Payload for Geophysical Research and Application (CHAMP) and Satélite de Aplicaciones Científicas-C (SAC-C) satellites that provide several retrieved refractivity profiles in the simulated domain near the initialization time. Through 3DVAR, the observed refractivity can be quickly ingested into the model initial conditions to recover the information over the ocean. The initial moisture increments from ingested GPS refractivity soundings exhibit a maximum magnitude of about 1.5 g kg−1 associated with temperature increments of generally less than 0.2°C. The differences between the model local refractivity and the observed refractivity are less than 3% with a maximum magnitude of about 10 units. Pronounced increments from an occultation point are found within an influential radius of 500–600 km only. For the simulation without the assimilation of GPS refractivity (the no-GPS run), the simulated Typhoon Nari coherently moves southwestward toward Taiwan early in the simulation but then exhibits a westward track along the northwest of Taiwan after landfall. With GPS refractivity assimilated, the simulated westward track in the no-GPS run is closer to the west coast. During landfall, the cloud convection associated with the intense vortex core encounters the Central Mountain Range (CMR) and produces torrential rainfalls along its northwestern slope. Both the GPS run and the no-GPS run capture the observed feature of very intense rainfall over the southwestern slope base of the CMR later in the simulation, while the intensity as well as the track is improved in the GPS run. In the other case (Nakri), the simulated rainfall distributions, in general, are similar for both the GPS run and the no-GPS run; however, the GPS run exhibits a more pronounced low to the southeast of Taiwan, which results in more intense rainfall in the northeast of Taiwan as observed. Both GPS runs for Nari and Nakri show improved skills in 24-h accumulated rainfall prediction, in particular, at later stages, as supported by higher threat scores and smaller root-mean-square errors against observations over the island. This positive impact can be attributed largely to the fact that the accumulative effects from assimilation of initial GPS refractivity soundings are instrumental to model performance. A cycling 3DVAR scheme is also explored in the simulation for Nari to investigate the impact of complementary NASA Quick Scatterometer (QuikSCAT) near-surface wind observations on model prediction. When such observed near-surface wind is assimilated into reinitialization at a later integration time, the track prediction is further improved and thus the prediction for accumulated rainfall is improved as well.

scholarly journals The Impact of Grid and Spectral Nudging on the Variance of the Near-Surface Wind Speed

2015 ◽  
Vol 54 (5) ◽  
pp. 1021-1038 ◽  
Author(s):  
Claire Louise Vincent ◽  
Andrea N. Hahmann
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Surface Wind ◽  
Ground Level ◽  
Near Surface ◽  
Spectral Nudging ◽  
Outer Domain ◽  
The Impact

AbstractGrid and spectral nudging are effective ways of preventing drift from large-scale weather patterns in regional climate models. However, the effect of nudging on the wind speed variance is unclear. In this study, the impact of grid and spectral nudging on near-surface and upper boundary layer wind variance in the Weather Research and Forecasting Model is analyzed. Simulations are run on nested domains with horizontal grid spacing of 15 and 5 km over the Baltic Sea region. For the 15-km domain, 36-h simulations initialized each day are compared with 11-day simulations with either grid or spectral nudging at and above 1150 m above ground level (AGL). Nested 5-km simulations are not nudged directly but inherit boundary conditions from the 15-km experiments. Spatial and temporal spectra show that grid nudging causes smoothing of the wind in the 15-km domain at all wavenumbers, both at 1150 m AGL and near the surface where nudging is not applied directly, while spectral nudging mainly affects longer wavenumbers. Maps of mesoscale variance show spatial smoothing for both grid and spectral nudging, although the effect is less pronounced for spectral nudging. On the inner, 5-km domain, an indirect smoothing impact of nudging is seen up to 200 km inward from the dominant inflow boundary at 1150 m AGL, but there is minimal smoothing from the nudging near the surface, indicating that nudging an outer domain is an appropriate configuration for wind-resource modeling.

scholarly journals Precipitation Modulation by the Saint Lawrence River Valley in Association with Transitioning Tropical Cyclones*

2013 ◽  
Vol 28 (2) ◽  
pp. 331-352 ◽  
Author(s):  
Shawn M. Milrad ◽  
Eyad H. Atallah ◽  
John R. Gyakum
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Surface Wind ◽  
Warm Season ◽  
Temperature Inversion ◽  
River Valley ◽  
Eastern Canada ◽  
Near Surface ◽  
The Impact ◽  
Pressure Driven

Abstract The St. Lawrence River valley (SLRV) is an important orographic feature in eastern Canada that can affect surface wind patterns and contribute to locally higher amounts of precipitation. The impact of the SLRV on precipitation distributions associated with transitioning, or transitioned, tropical cyclones that approached the region is assessed. Such cases can result in heavy precipitation during the warm season, as during the transition of Hurricane Ike (2008). Thirty-eight tropical cyclones tracked within 500 km of the SLRV from 1979 to 2011. Utilizing the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR), 19 of the 38 cases (group A) had large values of ageostrophic frontogenesis within and parallel to the SLRV, in a region of northeasterly surface winds associated with pressure-driven wind channeling. Using composite and case analyses, results show that the heaviest precipitation is often located within the SLRV, regardless of the location of large-scale forcing for ascent, and is concomitant with ageostrophic frontogenesis. The suggested physical pathway for precipitation modulation in the SLRV is as follows. Valley-induced near-surface ageostrophic frontogenesis is due to pressure-driven wind channeling as a result of the along-valley pressure gradient [typically exceeding 0.4 hPa (100 km)−1] established by the approaching cyclone. Near-surface cold-air advection as a result of the northeasterly pressure-driven channeling results in a temperature inversion, similar to what is observed in cool-season wind-channeling cases. The ageostrophic frontogenesis, acting as a mesoscale ascent-focusing mechanism, helps air parcels to rise above the temperature inversion into a conditionally unstable atmosphere, which results in enhanced precipitation focused along the SLRV.

scholarly journals Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 136
Author(s):  
Yahya Darmawan ◽  
Huang-Hsiung Hsu ◽  
Jia-Yuh Yu
Keyword(s):  
Large Scale ◽  
Precipitation Variability ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Moisture Budget ◽  
Large Scale Circulation ◽  
Budget Analysis ◽  
Sumatra Island ◽  
Precipitation Anomalies ◽  
The Impact

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

New directional wave observations from CFOSAT : impact on ocean/wave coupling in the Southern Ocean

2021 ◽  
Author(s):  
Lotfi Aouf ◽  
Daniele Hauser ◽  
Stephane Law-Chune ◽  
Bertrand chapron ◽  
Alice Dalphinet ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Surface Wind ◽  
Bias Reduction ◽  
Ocean Wave ◽  
Wave Number ◽  
Geophysical Research ◽  
Wave Coupling ◽  
Ocean Region ◽  
Directional Wave ◽  
The Impact

<p>The Southern ocean is a complex ocean region with uncertainties related to surface wind forcing and fluxes exchanges at the air/sea interface. The improvement of wind wave generation in this ocean region is crucial for climate studies. With CFOSAT satellite mission, the SWIM instrument provides directional wave spectra for wavelengths from 70 to 500 m, which shed light on the role of correcting the wave direction and peak wave number of dominant wave trains in the wind-waves growth phase. This consequently induced a better energy transfer between waves and a significant bias reduction of wave height in the Southern Ocean (Aouf et al. 2020). The objective of this work is to extend the analysis of the impact of the assimilation of wave number components from SWIM wave partitions on the ocean/wave coupling. To this end, coupled simulations of the wave model MFWAM and the ocean model NEMO are performed during the southern winter period of 2019 (May-July). We have examined the MFWAM/NEMO coupling with and without the assimilation of the SWIM mean wave number components. Several coupling processes related to Stokes drift, momentum flux stress and wave breaking inducing turbulence in the ocean mixing layer have been analyzed. We also compared the coupled runs with a control run without wave forcing in order to evaluate the impact of the assimilation. The results of coupled simulations have been validated with satellite Sea Surface Temperature and available surface currents data over the southern ocean. We also investigated the impact of the assimilation during severe storms with unlimited fetch conditions.</p><p>Further discussions and conclusions will be commented in the final paper.</p><p>Aouf L., New directional wave satellite observations : Towards improved wave forecasting and climate description in Southern Ocean, Geophysical Research Letters, DOI: 10.1029/2020GL091187 (in production).</p><p> </p><div> <div> <div></div> <div>What do you want to do ?</div> New mail</div> </div><div><img></div>

scholarly journals Impacts of Large-Scale Circulation on Urban Ambient Concentrations of Gaseous Elemental Mercury in New York, USA

2017 ◽  
Author(s):  
Huiting Mao ◽  
Dolly Hall ◽  
Zhuyun Ye ◽  
Ying Zhou ◽  
Dirk Felton ◽  
...  
Keyword(s):  
New York ◽  
North American ◽  
Large Scale ◽  
Measurement Data ◽  
Elemental Mercury ◽  
Urban Site ◽  
Large Scale Circulation ◽  
Gaseous Elemental Mercury ◽  
The North ◽  
The Impact

Abstract. The impact of large-scale circulation on urban gaseous elemental mercury (GEM) was investigated through analysis of 2008–2015 measurement data from an urban site in New York City (NYC), New York, USA. Distinct annual cycles were observed in 2009–2010 with mixing ratios in warm seasons (i.e. spring–summer) 10–20 ppqv (~ 10 %–25 %) higher than in cool seasons (i.e. fall–winter). This annual cycle was disrupted in 2011 by an anomalously strong influence of the North American trough in that warm season and was reproduced in 2014 with annual amplitude enhanced up to ~ 70 ppqv associated with a particularly strong Bermuda High. North American trough axis index (TAI) and intensity index (TII) were used to characterize the effect of the North American trough on NYC GEM especially in winter and summer. The intensity and position of the Bermuda High had a significant impact on GEM in warm seasons supported by a strong correlation (r reaching 0.96, p 

scholarly journals The Effects of Assimilating Conventional and ATOVS Data on Forecasted Near-Surface Wind with WRF-3DVAR

2015 ◽  
Vol 143 (1) ◽  
pp. 153-164 ◽  
Author(s):  
Feimin Zhang ◽  
Yi Yang ◽  
Chenghai Wang
Keyword(s):  
Data Assimilation ◽  
Surface Wind ◽  
Lower Atmosphere ◽  
Observation Data ◽  
Initial Field ◽  
Infrared Observation ◽  
Forecast Performance ◽  
Near Surface ◽  
The Impact ◽  
Positive Effect

Abstract In this paper, the Weather Research and Forecasting (WRF) Model with the three-dimensional variational data assimilation (WRF-3DVAR) system is used to investigate the impact on the near-surface wind forecast of assimilating both conventional data and Advanced Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (ATOVS) radiances compared with assimilating conventional data only. The results show that the quality of the initial field and the forecast performance of wind in the lower atmosphere are improved in both assimilation cases. Assimilation results capture the spatial distribution of the wind speed, and the observation data assimilation has a positive effect on near-surface wind forecasts. Although the impacts of assimilating ATOVS radiances on near-surface wind forecasts are limited, the fine structure of local weather systems illustrated by the WRF-3DVAR system suggests that assimilating ATOVS radiances has a positive effect on the near-surface wind forecast under conditions that ATOVS radiances in the initial condition are properly amplified. Assimilating conventional data is an effective approach for improving the forecast of the near-surface wind.

scholarly journals Assessing the Impact of Changes in Land Surface Conditions on WRF Predictions in Arid Regions

2020 ◽  
Vol 21 (12) ◽  
pp. 2829-2853 ◽  
Author(s):  
Marouane Temimi ◽  
Ricardo Fonseca ◽  
Narendra Nelli ◽  
Michael Weston ◽  
Mohan Thota ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Soil Texture ◽  
Land Surface ◽  
Surface Wind ◽  
Surface Fluxes ◽  
Abu Dhabi ◽  
Horizontal Wind ◽  
Cold Bias ◽  
Near Surface ◽  
The Impact

AbstractA thorough evaluation of the Weather Research and Forecasting (WRF) Model is conducted over the United Arab Emirates, for the period September 2017–August 2018. Two simulations are performed: one with the default model settings (control run), and another one (experiment) with an improved representation of soil texture and land use land cover (LULC). The model predictions are evaluated against observations at 35 weather stations, radiosonde profiles at the coastal Abu Dhabi International Airport, and surface fluxes from eddy-covariance measurements at the inland city of Al Ain. It is found that WRF’s cold temperature bias, also present in the forcing data and seen almost exclusively at night, is reduced when the surface and soil properties are updated, by as much as 3.5 K. This arises from the expansion of the urban areas, and the replacement of loamy regions with sand, which has a higher thermal inertia. However, the model continues to overestimate the strength of the near-surface wind at all stations and seasons, typically by 0.5–1.5 m s−1. It is concluded that the albedo of barren/sparsely vegetated regions in WRF (0.380) is higher than that inferred from eddy-covariance observations (0.340), which can also explain the referred cold bias. At the Abu Dhabi site, even though soil texture and LULC are not changed, there is a small but positive effect on the predicted vertical profiles of temperature, humidity, and horizontal wind speed, mostly between 950 and 750 hPa, possibly because of differences in vertical mixing.

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