scholarly journals Tropospheric Turbulence over the Tropical Open Ocean: Role of Gravity Waves

2017 ◽  
Vol 74 (4) ◽  
pp. 1249-1271 ◽  
Author(s):  
H. Bellenger ◽  
R. Wilson ◽  
J. L. Davison ◽  
J. P. Duvel ◽  
W. Xu ◽  
...  
Keyword(s):  
Dynamic Instability ◽  
Wave Spectrum ◽  
Lower Troposphere ◽  
Static Stability ◽  
Vertical Shear ◽  
Statistical Characteristics ◽  
Horizontal Wind ◽  
Large Set ◽  
Ascent Rate ◽  
The Indian Ocean

Abstract A large set of soundings obtained in the Indian Ocean during three field campaigns is used to provide statistical characteristics of tropospheric turbulence and its link with gravity wave (GW) activity. The Thorpe method is used to diagnose turbulent regions of a few hundred meters depth. Above the mixed layer, turbulence frequency varies from ~10% in the lower troposphere up to ~30% around 12-km height. GWs are captured by their signature in horizontal wind, normalized temperature, and balloon vertical ascent rate. These parameters emphasize different parts of the wave spectrum from longer to shorter vertical wavelengths. Composites are constructed in order to reveal the vertical structure of the waves and their link with turbulence. The relatively longer-wavelength GWs described by their signature in temperature (GWTs) are more active in the lower troposphere, where they are associated with clear variations in moisture. Turbulence is then associated with minimum static stability and vertical shear, stressing the importance of the former and the possibility of convective instability. Conversely, the short waves described by their signature in balloon ascent rate (GWws) are detected primarily in the upper troposphere, and their turbulence is associated with a vertical shear maximum, suggesting the importance of dynamic instability. Furthermore, GWws appear to be linked with local convection, whereas GWTs are more active in suppressed and dry phases in particular of the Madden–Julian oscillation. These waves may be associated with remote sources, such as organized convection or local fronts, such as those associated with dry-air intrusions.

scholarly journals The Evolution of Hurricane Humberto (2001)

2014 ◽  
Vol 71 (4) ◽  
pp. 1276-1291 ◽  
Author(s):  
Klaus Dolling ◽  
Gary M. Barnes
Keyword(s):  
Numerical Simulations ◽  
Temperature Anomaly ◽  
Lower Troposphere ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Maximum Temperature ◽  
Warm Core ◽  
Warm Anomaly ◽  
Surface Heat Exchange ◽  
Environmental Air

Abstract In 2001, the National Oceanic and Atmospheric Administration and the National Aeronautical and Space Administration marshaled their resources to sample Hurricane Humberto for 3 successive days during the fourth Convection and Moisture Experiment (CAMEX-4). Humberto developed from a tropical storm into a category-2 hurricane despite the deep-layer vertical shear of the environmental horizontal wind (VWS) increasing markedly on the second and third days of sampling. As exhibited in earlier studies, the eyewall convection developed an azimuthal wavenumber-1 (n = 1) asymmetry as the VWS increased. Horizontal divergence and vertical stability within 100 km of the eye exhibited persistent relationships to the VWS vector. The warm core evolved in an unexpected way. The warm anomaly was initially located in the lower troposphere and built upward as the storm intensified. The maximum temperature anomaly remained in the lower troposphere on all 3 days while the development of the upper-tropospheric warm anomaly appeared to be inhibited by the increasing VWS and the entrainment of dry environmental air into the core at midlevels. The warm core of this higher-latitude (33°N) storm displayed large differences when compared to most numerical simulations, wind-induced surface heat exchange theory, and observations of tropical cyclones in the deep tropics acquired nearly 50 years ago. The results were similar to some recent numerical simulations.

Quasigeostrophic Controls on Precipitating Ascent in Monsoon Depressions

2019 ◽  
Vol 77 (4) ◽  
pp. 1213-1232 ◽  
Author(s):  
Varun S. Murthy ◽  
William R. Boos
Keyword(s):  
Surface Wind ◽  
Lower Troposphere ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Convective Heating ◽  
Moist Convection ◽  
Modeling Framework ◽  
Surface Enthalpy ◽  
Monsoon Depressions ◽  
Enhanced Surface

Abstract South Asian monsoon depressions are convectively coupled cyclonic vortices that form and intensify in a region of easterly vertical shear of the horizontal wind. Observations of maximum precipitation downshear of the cyclonic center have led to prior theories of quasigeostrophic (QG) control of moist convection in these storms. This study examines the interaction between adiabatic QG lifting and moist convection in monsoon depressions using an atmospheric reanalysis and idealized model. Inversion of the QG omega equation in the reanalysis shows that in the downshear, heavily precipitating region, adiabatic QG ascent, due to advection of vorticity and temperature, is comparable to diabatic ascent in the lower troposphere, while diabatic ascent dominates in the middle and upper troposphere. The causal influence of adiabatic QG lifting on precipitating ascent in monsoon depressions is then examined in the column QG modeling framework, where moist convection evolves in the presence of vorticity and temperature advection. The heavy observed precipitation rates are only simulated when moist convective heating amplifies QG ascent, with this interaction accounting for roughly 40% of the increase in precipitation relative to the basic state. Another 40% of this increase is produced by enhanced surface wind speed in the surface enthalpy flux parameterization, which represents the effect of cyclonic winds in the monsoon depression. Horizontal advection of the mean-state poleward moisture gradient accounts for the remaining 20% of the precipitation increase. In the upshear region, adiabatic QG subsidence and horizontal moisture advection both suppress precipitation, and are opposed by wind-enhanced surface enthalpy fluxes.

scholarly journals Diagnosing ISO Forecast from GloSea5 Using Dynamic-Oriented ISO Theory

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 114
Author(s):  
Young-Min Yang ◽  
Taehyoun Shim ◽  
Ja-Yeon Moon ◽  
Ki-Young Kim ◽  
Yu-Kyung Hyun
Keyword(s):  
Indian Ocean ◽  
Deep Convection ◽  
Intraseasonal Oscillation ◽  
Lower Troposphere ◽  
Moisture Convergence ◽  
Lower Atmosphere ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Kelvin Wave ◽  
The Indian Ocean

A Madden–Jillian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) are important climate variabilities, which affect a forecast of weather and climate. In this study, the MJO and the BSISO hindcasts from the Global Seasonal Forecast System, version 5 (GS5) were diagnosed using dynamic-oriented theories. We additionally analyzed the GS5 climatological run to identify whether the weakness of the GS5 hindcast results from the model physics or initialization processes. The GS5 hindcast captures three-dimensional dynamics and thermodynamics structure of MJO eastward propagation well in the Indian Ocean. The model produces the boundary layer (BL) moisture convergence anomalies to the east of the MJO deep precipitation with easterly anomalies associated with the Kelvin wave. The enhanced BL moisture convergence increases upward transport of moisture from the surface to the lower troposphere, inducing the moist lower troposphere and the positive convective instability by destabilization of the lower atmosphere and, thus, generating the next convection to the east of MJO deep convection and promoting MJO eastward propagation. However, the signal for eastward propagation is relatively weak in the Maritime Continent (MC) and the Western Pacific (WP). To improve the MJO eastward propagation in the MC and WP, improved heating induced by shallow (or congestus) clouds interacting with enhanced BL dynamics may be required. On the other hand, the GS5 hindcast reproduces the BSISO northward propagation reasonably well in the Indian Ocean, which is attributed to positive vorticity anomalies induced by strong vertical shear.

scholarly journals Effects of atmospheric dynamics and aerosols on the fraction of supercooled water clouds

2017 ◽  
Vol 17 (3) ◽  
pp. 1847-1863 ◽  
Author(s):  
Jiming Li ◽  
Qiaoyi Lv ◽  
Min Zhang ◽  
Tianhe Wang ◽  
Kazuaki Kawamoto ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Meteorological Parameters ◽  
Temporal Correlation ◽  
Supercooled Liquid ◽  
Satellite Observation ◽  
Static Stability ◽  
Global Scale ◽  
Atmospheric Dynamics ◽  
Horizontal Wind

Abstract. Based on 8 years of (January 2008–December 2015) cloud phase information from the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud Product (GOCCP), aerosol products from CALIPSO and meteorological parameters from the ERA-Interim products, the present study investigates the effects of atmospheric dynamics on the supercooled liquid cloud fraction (SCF) during nighttime under different aerosol loadings at global scale to better understand the conditions of supercooled liquid water gradually transforming to ice phase. Statistical results indicate that aerosols' effect on nucleation cannot fully explain all SCF changes, especially in those regions where aerosols' effect on nucleation is not a first-order influence (e.g., due to low ice nuclei aerosol frequency). By performing the temporal and spatial correlations between SCFs and different meteorological factors, this study presents specifically the relationship between SCF and different meteorological parameters under different aerosol loadings on a global scale. We find that the SCFs almost decrease with increasing of aerosol loading, and the SCF variation is closely related to the meteorological parameters but their temporal relationship is not stable and varies with the different regions, seasons and isotherm levels. Obviously negative temporal correlations between SCFs versus vertical velocity and relative humidity indicate that the higher vertical velocity and relative humidity the smaller SCFs. However, the patterns of temporal correlation for lower-tropospheric static stability, skin temperature and horizontal wind are relatively more complex than those of vertical velocity and humidity. For example, their close correlations are predominantly located in middle and high latitudes and vary with latitude or surface type. Although these statistical correlations have not been used to establish a certain causal relationship, our results may provide a unique point of view on the phase change of mixed-phase cloud and have potential implications for further improving the parameterization of the cloud phase and determining the climate feedbacks.

scholarly journals Systematic Variation in Wintertime Precipitation in East Asia by MJO-Induced Extratropical Vertical Motion

2008 ◽  
Vol 21 (4) ◽  
pp. 788-801 ◽  
Author(s):  
Jee-Hoon Jeong ◽  
Baek-Min Kim ◽  
Chang-Hoi Ho ◽  
Yeon-Hee Noh
Keyword(s):  
East Asia ◽  
Large Scale ◽  
Diabatic Heating ◽  
Daily Precipitation ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Mean Value ◽  
Asian Countries ◽  
The Indian Ocean ◽  
Omega Equation

Abstract The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden–Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974–2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3–4 mm day−1, which corresponds to the climatological winter-mean value. Composite analysis with respect to the MJO suggests that the MJO–precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia upper-tropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.

scholarly journals On strongly nonlinear gravity waves in a vertically sheared atmosphere

2020 ◽  
Vol 6 (1) ◽  
pp. 63-74
Author(s):  
Mark Schlutow ◽  
Georg S. Voelker
Keyword(s):  
Gravity Waves ◽  
Lower Layer ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Necessary Condition ◽  
Mean Flow ◽  
Individual Layer ◽  
Strongly Nonlinear ◽  
The Mean ◽  
The Stability

Abstract We investigate strongly nonlinear stationary gravity waves which experience refraction due to a thin vertical shear layer of horizontal background wind. The velocity amplitude of the waves is of the same order of magnitude as the background flow and hence the self-induced mean flow alters the modulation properties to leading order. In this theoretical study, we show that the stability of such a refracted wave depends on the classical modulation stability criterion for each individual layer, above and below the shearing. Additionally, the stability is conditioned by novel instability criteria providing bounds on the mean-flow horizontal wind and the amplitude of the wave. A necessary condition for instability is that the mean-flow horizontal wind in the upper layer is stronger than the wind in the lower layer.

scholarly journals Simulation of the Madden–Julian Oscillation in the NCAR CCM3 Using a Revised Zhang–McFarlane Convection Parameterization Scheme

2005 ◽  
Vol 18 (19) ◽  
pp. 4046-4064 ◽  
Author(s):  
Guang J. Zhang ◽  
Mingquan Mu
Keyword(s):  
Relative Humidity ◽  
Indian Ocean ◽  
Zonal Wind ◽  
Lower Troposphere ◽  
Parameterization Scheme ◽  
Madden Julian Oscillation ◽  
Shallow Convection ◽  
Time Period ◽  
The Indian Ocean ◽  
Convection Parameterization

Abstract This study presents the simulation of the Madden–Julian oscillation (MJO) in the NCAR CCM3 using a modified Zhang–McFarlane convection parameterization scheme. It is shown that, with the modified scheme, the intraseasonal (20–80 day) variability in precipitation, zonal wind, and outgoing longwave radiation (OLR) is enhanced substantially compared to the standard CCM3 simulation. Using a composite technique based on the empirical orthogonal function (EOF) analysis, the paper demonstrates that the simulated MJOs are in better agreement with the observations than the standard model in many important aspects. The amplitudes of the MJOs in 850-mb zonal wind, precipitation, and OLR are comparable to those of the observations, and the MJOs show clearly eastward propagation from the Indian Ocean to the Pacific. In contrast, the simulated MJOs in the standard CCM3 simulation are weak and have a tendency to propagate westward in the Indian Ocean. Nevertheless, there remain several deficiencies that are yet to be addressed. The time period of the MJOs is shorter, about 30 days, compared to the observed time period of 40 days. The spatial scale of the precipitation signal is smaller than observed. Examination of convective heating from both deep and shallow convection and its relationship with moisture anomalies indicates that near the mature phase of the MJO, regions of shallow convection developing ahead of the deep convection coincide with regions of positive moisture anomalies in the lower troposphere. This is consistent with the recent observations and theoretical development that shallow convection helps to precondition the atmosphere for MJO by moistening the lower troposphere. Sensitivity tests are performed on the individual changes in the modified convection scheme. They show that both change of closure and use of a relative humidity threshold for the convection trigger play important roles in improving the MJO simulation. Use of the new closure leads to the eastward propagation of the MJO and increases the intensity of the MJO signal in the wind field, while imposing a relative humidity threshold enhances the MJO variability in precipitation.

scholarly journals Static stability predicts the continuum of interleg coordination patterns in Drosophila

2018 ◽  
Author(s):  
Nicholas S. Szczecinski ◽  
Till Bockemühl ◽  
Alexander S. Chockley ◽  
Ansgar Büschges
Keyword(s):  
Experimental Data ◽  
Static Stability ◽  
Fruit Flies ◽  
Coordination Pattern ◽  
Large Set ◽  
Summary Statement ◽  
Walking Speeds ◽  
Coordination Patterns ◽  
Phase Relationships ◽  
The Continuum

AbstractDuring walking, insects must coordinate the movements of their six legs for efficient locomotion. This interleg coordination is speed-dependent; fast walking in insects is associated with tripod coordination patterns, while slow walking is associated with more variable, tetrapod-like patterns. To date, however, there has been no comprehensive explanation as to why these speed-dependent shifts in interleg coordination should occur in insects. Tripod coordination would be sufficient at low walking speeds. The fact that insects use a different interleg coordination pattern at lower speeds suggests that it is more optimal or advantageous at these speeds. Furthermore, previous studies focused on discrete tripod and tetrapod coordination patterns. Experimental data, however, suggest that changes observed in interleg coordination are part of a speed-dependent spectrum. Here, we explore these issues in relation to static stability as an important aspect of interleg coordination in Drosophila. We created a model that uses basic experimentally measured parameters in fruit flies to find the interleg phase relationships that maximize stability for a given walking speed. Based on this measure, the model predicted a continuum of interleg coordination patterns spanning the complete range of walking speeds. Furthermore, for low walking speeds the model predicted tetrapod-like patterns to be most stable, while at high walking speeds tripod coordination emerged as most optimal. Finally, we validated the basic assumption of a continuum of interleg coordination patterns in a large set of experimental data from walking fruit flies and compared these data with the model-based predictions.Summary statementA simple stability-based modelling approach can explain why walking insects use different leg coordination patterns in a speed-dependent way.

scholarly journals Analyzing the basic meteorological aspects of a particulate air pollution episode over the industrial area of Northwestern Greece during the November of 2009

2013 ◽  
Vol 15 (2) ◽  
pp. 241-253 ◽  
Keyword(s):  
Air Pollution ◽  
Particulate Matter ◽  
Wind Field ◽  
Lower Troposphere ◽  
Airborne Particulate Matter ◽  
Radical Change ◽  
Industrial Area ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Pollution Episode

The complex terrain basin of Amyntaio – Ptolemais – Kozani in Western Macedonia of Greece is an area characterized by increased industrial activity and therefore it demands continuous and assiduous environmental monitoring. A prolonged particulate matter air pollution episode was recorded in the area during November 2009. Basic meteorological aspects are analyzed, during the episode period. Daily and hourly PM10 and PM2.5 concentration measurements were used along with surface and lower atmosphere hourly meteorological parameters from 13 measuring stations. The observational data were supported by data produced by the meteorological component of an air pollution model. The overall analysis showed that the episode was primarily the result of the synoptic setting of the middle and lower troposphere. An Omega blocking pattern which gradually transformed to a high-over-low pattern prevailed over central and southern Europe during the episode’s period. The examination of the vertical wind field in the lower troposphere and appropriate stability indices, revealed a continuous absence of significant convection. The weak horizontal wind field near the surface and the reduced mixing height combined with the lack of synoptic forcing resulted in the trapping of the pollutants in the lower troposphere and the recording of increased airborne particulate matter concentrations. The radical change of the synoptic setting in the first days of December marked the end of the episode.

scholarly journals Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

Atmosphere ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 230
Author(s):  
Inyeob La ◽  
Seong Soo Yum ◽  
Ismail Gultepe ◽  
Jae Min Yeom ◽  
Jae In Song ◽  
...  
Keyword(s):  
Periodic Oscillation ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Simultaneous Increase ◽  
Mountainous Region ◽  
Helmholtz Instability ◽  
Radiation Fog ◽  
Quasi Periodic Oscillation ◽  
Time Frequency ◽  
Atmospheric Variables

To enhance our understanding of fog processes over complex terrain, various fog events that occurred during the International Collaborative Experiments for Pyeongchang 2018 Winter Olympics and Paralympics (ICE-POP) campaign were selected. Investigation of thermodynamic, dynamic, and microphysical conditions within fog layers affected by quasi-periodic oscillation of atmospheric variables was conducted using observations from a Fog Monitor-120 (FM-120) and other in-situ meteorological instruments. A total of nine radiation fog cases that occurred in the autumn and winter seasons during the campaign over the mountainous region of Pyeongchang, Korea were selected. The wavelet analysis was used to study quasi-period oscillations of dynamic, microphysical, and thermodynamic variables. By decomposing the time series into the time-frequency space, we can determine both dominant periods and how these dominant periods change in time. Quasi-period oscillations of liquid water content (LWC), pressure, temperature, and horizontal/vertical velocity, which have periods of 15–40 min, were observed during the fog formation stages. We hypothesize that these quasi-periodic oscillations were induced by Kelvin–Helmholtz instability. The results suggest that Kelvin–Helmholtz instability events near the surface can be explained by an increase in the vertical shear of horizontal wind and by a simultaneous increase in wind speed when fog forms. In the mature stages, fluctuations of the variables did not appear near the surface anymore.

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