scholarly journals Numerical simulations of contrail-to-cirrus transition – Part 1: An extensive parametric study

2009 ◽  
Vol 9 (4) ◽  
pp. 14901-14953 ◽  
Author(s):  
S. Unterstrasser ◽  
K. Gierens
Keyword(s):  
Relative Humidity ◽  
Numerical Simulations ◽  
Water Vapour ◽  
Parametric Study ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Ice Crystals ◽  
Les Model ◽  
Dominant Parameter

Abstract. Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties on relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on most contrail properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.

scholarly journals Numerical simulations of contrail-to-cirrus transition – Part 1: An extensive parametric study

2010 ◽  
Vol 10 (4) ◽  
pp. 2017-2036 ◽  
Author(s):  
S. Unterstrasser ◽  
K. Gierens
Keyword(s):  
Optical Properties ◽  
Relative Humidity ◽  
Numerical Simulations ◽  
Parametric Study ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Ice Crystals ◽  
Les Model ◽  
Dominant Parameter

Abstract. Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties to relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on optical properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.

scholarly journals A statistical examination of the effects of stratospheric sulphate geoengineering on tropical storm genesis

2018 ◽  
Author(s):  
Qin Wang ◽  
John C. Moore ◽  
Duoying Ji
Keyword(s):  
Relative Humidity ◽  
Wind Shear ◽  
Climate Models ◽  
Climate Model ◽  
Vertical Wind Shear ◽  
Stratospheric Aerosol ◽  
Vertical Wind ◽  
Radiative Heating ◽  
Cmip5 Models ◽  
The North

Abstract. The thermodynamics of the ocean and atmosphere partly determine variability in tropical cyclone (TC) number and intensity and are readily accessible from climate model output, but a complete description of TC variability requires much more dynamical data than climate models can provide at present. Genesis potential index (GPI) and ventilation index (VI) are combinations of potential intensity, vertical wind shear, relative humidity, midlevel entropy deficit, and absolute vorticity that can quantify both thermodynamic and dynamic forcing of TC activity under different climate states. Here we use six CMIP5 models that have run the RCP4.5 experiment and the Geoengineering Model Intercomparison Project (GeoMIP) stratospheric aerosol injection G4 experiment, to calculate the two TC indices over the 2020 to 2069 period across the 6 ocean basins that generate tropical cyclones. Globally, GPI under G4 is lower than under RCP4.5, though both have a slight increasing trend. Spatial patterns in the effectiveness of geoengineering show reductions in TC in the North Atlantic basin, and Northern Indian Ocean in all models except NorESM1-M. In the North Pacific, most models also show relative reductions under G4. Most models project potential intensity and relative humidity to be the dominant variables affecting genesis potential. Changes in vertical wind shear are significant, but both it and vorticity exhibit relatively small changes with large variation across both models and ocean basins. We find that tropopause temperature is not a useful addition to sea surface temperature in projecting TC genesis, despite radiative heating of the stratosphere due to the aerosol injection, and heating of the upper troposphere affecting static stability and potential intensity. Thus, simplified statistical methods that quantify the thermodynamic state of the major genesis basins may reasonably be used to examine stratospheric aerosol geoengineering impacts on TC activity.

scholarly journals Numerical Simulations of the Impacts of the Saharan Air Layer on Atlantic Tropical Cyclone Development

2009 ◽  
Vol 22 (23) ◽  
pp. 6230-6250 ◽  
Author(s):  
Donglian Sun ◽  
W. K. M. Lau ◽  
Menas Kafatos ◽  
Zafer Boybeyi ◽  
Gregory Leptoukh ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Air Entrainment ◽  
Vertical Wind ◽  
Environmental Stability ◽  
Western Atlantic ◽  
Dry Air ◽  
Saharan Air Layer

Abstract In this study, the role of the Saharan air layer (SAL) is investigated in the development and intensification of tropical cyclones (TCs) via modifying environmental stability and moisture, using multisensor satellite data, long-term TC track and intensity records, dust data, and numerical simulations with a state-of-the-art Weather Research and Forecasting model (WRF). The long-term relationship between dust and Atlantic TC activity shows that dust aerosols are negatively associated with hurricane activity in the Atlantic basin, especially with the major hurricanes in the western Atlantic region. Numerical simulations with the WRF for specific cases during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) experiment show that, when vertical temperature and humidity profiles from the Atmospheric Infrared Sounder (AIRS) were assimilated into the model, detailed features of the warm and dry SAL, including the entrainment of dry air wrapping around the developing vortex, are well simulated. Active tropical disturbances are found along the southern edge of the SAL. The simulations show an example where the dry and warm air of the SAL intruded into the core of a developing cyclone, suppressing convection and causing a spin down of the vortical circulation. The cyclone eventually weakened. To separate the contributions from the warm temperature and dry air associated with the SAL, two additional simulations were performed, one assimilating only AIRS temperature information (AIRST) and one assimilating only AIRS humidity information (AIRSH) while keeping all other conditions the same. The AIRST experiments show almost the same simulations as the full AIRS assimilation experiments, whereas the AIRSH is close to the non-AIRS simulation. This is likely due to the thermal structure of the SAL leading to low-level temperature inversion and increased stability and vertical wind shear. These analyses suggest that dry air entrainment and the enhanced vertical wind shear may play the direct roles in leading to the TC suppression. On the other hand, the warm SAL temperature may play the indirect effects by enhancing vertical wind shear; increasing evaporative cooling; and initiating mesoscale downdrafts, which bring dry air from the upper troposphere to the lower levels.

scholarly journals Seasonal Variation of Tropical Cyclone Genesis and the Related Large-Scale Environments: Comparison between the Bay of Bengal and Arabian Sea Sub-Basins

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1593
Author(s):  
Wei Duan ◽  
Junpeng Yuan ◽  
Xu Duan ◽  
Dian Feng
Keyword(s):  
Tropical Cyclone ◽  
Relative Humidity ◽  
Wind Shear ◽  
Monsoon Season ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Tropical Cyclone Genesis ◽  
Positive Contribution ◽  
Post Monsoon ◽  
Post Monsoon Season

Using tropical cyclone data along with sea surface temperature data (SST) and atmospheric circulation reanalysis data during the period of 1980–2019, the seasonal variation of tropical cyclone genesis (TCG), and the related oceanic and atmospheric environments over the Arabian Sea (AS) and Bay of Bengal (BOB) are compared and analyzed in detail. The results show that TCG in both the BOB and AS present bimodal seasonal variations, with two peak periods in the pre-monsoon and post-monsoon season, respectively. The frequencies of TCG in the BOB and AS are comparatively similar in the pre-monsoon season but significantly different in the post-monsoon season. During the post-monsoon season of October–November, the TCG frequency in the BOB is approximately 2.3 times higher than that of the AS. The vertical wind shear and relative humidity in the low- and middle-level troposphere are the two major contributing factors for TCG, and the combination of these two factors determines the bimodal seasonal cycle of TCG in both the AS and BOB. In the pre-monsoon season, an increase in the positive contribution of vertical wind shear and a decrease in the negative contribution of relative humidity are collaboratively favorable for TCG in the AS and BOB. During the monsoon season, the relative humidity factor shows a significant and positive contribution to TCG, but its positive effect is offset by the strong negative effect of vertical wind shear and potential intensity, thus resulting in very low TCG in the AS and BOB. However, the specific relative contributions of each environmental factor to the TCG variations in the AS and BOB basins are quite different, especially in the post-monsoon season. In the post-monsoon season, the primary positive contributor to TCG in the AS basin is vertical wind shear, while the combined effect of vertical wind shear and relative humidity dominates in the BOB TCG. From the analysis of environmental factors, atmospheric circulations, and genesis potential index (GPI), the BOB is found to have more favorable TCG conditions than the AS, especially in the post-monsoon season.

Modulation of Tropical Cyclones over the Eastern Pacific by the Intraseasonal Variability Simulated in an AGCM

2012 ◽  
Vol 25 (19) ◽  
pp. 6524-6538 ◽  
Author(s):  
Xianan Jiang ◽  
Ming Zhao ◽  
Duane E. Waliser
Keyword(s):  
Relative Humidity ◽  
Wind Shear ◽  
Large Scale ◽  
Intraseasonal Variability ◽  
Vertical Wind Shear ◽  
Atmospheric Model ◽  
Horizontal Resolution ◽  
Vertical Wind ◽  
Eastern Pacific ◽  
Geophysical Fluid Dynamics Laboratory

Abstract This study illustrates that observed modulations of tropical cyclone (TC) genesis over the eastern Pacific (EPAC) by large-scale intraseasonal variability (ISV) are well represented in a recently developed high-resolution atmospheric model (HiRAM) at the NOAA/Geophysical Fluid Dynamics Laboratory (GFDL) with a horizontal resolution of about 50 km. Considering the intrinsic predictability of the ISV of 2–4 weeks, this analysis thus has significant implications for dynamically based TC predictions on intraseasonal time scales. Analysis indicates that the genesis potential index (GPI) anomalies associated with the ISV can generally well depict ISV modulations of EPAC TC genesis in both observations and HiRAM simulations. Further investigation is conducted to explore the key factors associated with ISV modulation of TC activity based on an analysis of budget terms of the observed GPI during the ISV life cycle. It is found that, while relative roles of GPI factors are dependent on ISV phase and location, lower-level cyclonic vorticity, enhanced midlevel relative humidity, and reduced vertical wind shear can all contribute to the observed active TC genesis over the EPAC during particular ISV phases. In general, the observed anomalous ISV patterns of these large-scale GPI factors are well represented in HiRAM. Model deficiencies are also noted particularly in the anomalous midlevel relative humidity patterns and amplitude of vertical wind shear associated with the EPAC ISV.

scholarly journals Eddy diffusion of water vapour and heat near the ground

1949 ◽  
Vol 198 (1052) ◽  
pp. 116-140 ◽  
Keyword(s):  
Temperature Gradient ◽  
Water Vapour ◽  
Wind Shear ◽  
Turbulent Transport ◽  
Heat Content ◽  
Vertical Wind Shear ◽  
Ground Surface ◽  
Vertical Wind ◽  
Wave Radiation ◽  
Stable Conditions

An experimental study has been made of the factors involved in the turbulent transport of water vapour and heat in the lowest layer of the atmosphere over well exposed level grassland. Measurements were made over periods of 1 hr. of the water loss from isolated but otherwise naturally exposed sections of the surface layers of the soil and quantitative arguments advanced for adopting them as a reasonable approximation to the true evaporation loss from the ground surface. The incoming and reflected components of solar radiation, the temperature distribution in the soil down to 16 in. and the vertical profiles of temperature, humidity and wind speed in the air up to a height of 2 m. were observed at the same time, and samples taken to provide necessary data on the physical properties of the soil. The net flux of long-wave radiation was computed from the temperature and humidity structure of the atmosphere as given by the present low-level measurements and routine upper-air soundings. The data prescribe the vertical turbulent flux and the vertical gradients of the water vapour and heat content of the air, from which maybe evaluated the vertical components of the eddy diffusivities for water vapour and heat ( K v and K H ) as customarily defined. In the absence of thermal stratification of the surface air layers K v is shown to be identical with the eddy diffusivity for momentum ( K m ) defined by the explicitly established logarithmic law relating the aerodynamic drag and vertical wind shear over a rough surface. The modification of K v by unstable and stable thermal stratifications and the rapid decrease of stability influence as the ground surface is approached are both quantitatively demonstrated, and a unique relation between parameters involving K v , the vertical wind shear and the vertical temperature gradient is indicated. No completely satisfactory a priori explanation can as yet be given for the latter relation, though in unstable conditions K v is found to be identical with K m computed from a recent wind-profile law which does not involve the temperature gradient explicitly and has only been established in functional form. Diroct comparison of K v and K H reveals a reasonable approach to equality in stable conditions but shows that the latter coefficient is systematically and substantially the greater in unstable conditions. The latter feature is qualitatively in keeping with recent trends in the theoretical concepts of turbulent transport. The bearing of the results on the problem of indirectly evaluating natural land evaporation is briefly discussed and attention drawn to the implied superiority of the present ‘ hydro-dynamical’ approach over the classical ‘heat-balance’ method.

The Dependence of Numerically Simulated Cyclic Mesocyclogenesis upon Environmental Vertical Wind Shear

2005 ◽  
Vol 133 (12) ◽  
pp. 3595-3623 ◽  
Author(s):  
Edwin J. Adlerman ◽  
Kelvin K. Droegemeier
Keyword(s):  
Steady State ◽  
Numerical Simulations ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Vertical Shear ◽  
Shear Distribution ◽  
Full Circle ◽  
Low Levels

Abstract Building upon the authors’ previous work that examined the dynamics of numerically simulated cyclic mesocyclogenesis and its dependence upon model physical and computational parameters, this study likewise uses idealized numerical simulations to investigate associated dependencies upon ambient vertical wind shear. Specifically, the authors examine variations in hodograph shape, shear magnitude, and shear distribution, leading to storms with behavior ranging from steady state to varying degrees of aperiodic occluding cyclic mesocyclogenesis. However, the authors also demonstrate that a different mode of nonoccluding cyclic mesocyclogenesis may occur in certain environments. Straight hodographs (unidirectional shear) produce only nonoccluding cyclic mesocyclogenesis. Introducing some curvature by adding a quarter circle of turning at low levels results in steady, nonoccluding, and occluding modes. When a higher degree of curvature is introduced—for example, turning through half and three-quarter circles—the tendency for nonoccluding behavior is diminished. None of the full-circle hodographs exhibited cycling during 4 h of simulation. Overall, within a given storm, the preferred mode of cycling is related principally to hodograph shape and magnitude of the ambient vertical shear.

scholarly journals Seasonal to Interannual Variability of Vertical Wind Shear and Its Relationship with Tropical Cyclogenesis in the Mozambique Channel

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 739
Author(s):  
Atanásio João Manhique ◽  
Isac Arnaldo Guirrugo ◽  
Bernardino João Nhantumbo ◽  
Alberto Francisco Mavume
Keyword(s):  
Relative Humidity ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Spatial Location ◽  
Relative Vorticity ◽  
Vertical Wind ◽  
Upper Atmosphere ◽  
Tropical Cyclogenesis ◽  
Southwest Indian Ocean ◽  
Mozambique Channel

This article explores the relationship between vertical wind shear (VWS) and tropical cyclone (TC) genesis in the Mozambique Channel (MC) for the period 1979–2019. Additionally, SST, low-level relative vorticity, 700 hPa relative humidity and upper-level divergence were also analyzed for the peak cyclogenesis months to explore their relative contributions. The analyses were done using NCEP/NCAR Reanalysis-1 for the atmospheric fields, monthly Optimum Interpolation SST V2, and for the cyclogenesis the TC best track data from the La Reunion–Regional Specialized Meteorological and Joint Typhoon Warning Centre. A total of 43 TCs generated in the MC were observed for the analysed period. The maximum frequency of cyclogenesis in the MC was observed during January and February and the spatial location of maximum TC genesis was coincident with the minimum values of the VWS. The VWS showed significant correlations with TC intensity, particularly when considering the upper atmosphere (200–500 hPa) or the bulk (200–850 hPa) VWS. The mean composites of the cyclogenesis months over the MC of SST, relative humidity at 700 hPa, divergence at upper atmosphere, showed significant values. However, linear correlations between these factors vs. TC genesis frequency and intensity were not significant. Analyses of interannual correlations between VWS and Niño-3.4 (subtropical southwest Indian Ocean dipole-SIOD) showed statistically significant positive (negative) correlations at different lags, suggesting that La Niña and the positive phase of SIOD conditions are favorable to weaker VWS and thus to intensification of TCs in the Mozambique Channel. Thirteen landfall cases were observed with seven over the Madagascar west coast and six over the Mozambique coast. The landfall over the Madagascar (Mozambique) coast was associated with strengthened (weakened) VWS.

scholarly journals An Observational Study of Mesoscale Convective Systems with Heavy Rainfall over the Korean Peninsula

2006 ◽  
Vol 21 (2) ◽  
pp. 125-148 ◽  
Author(s):  
Hyung Woo Kim ◽  
Dong Kyou Lee
Keyword(s):  
Observational Study ◽  
Korean Peninsula ◽  
Wind Shear ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Mesoscale Convective Systems ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract A heavy rainfall event induced by mesoscale convective systems (MCSs) occurred over the middle Korean Peninsula from 25 to 27 July 1996. This heavy rainfall caused a large loss of life and property damage as a result of flash floods and landslides. An observational study was conducted using Weather Surveillance Radar-1988 Doppler (WSR-88D) data from 0930 UTC 26 July to 0303 UTC 27 July 1996. Dominant synoptic features in this case had many similarities to those in previous studies, such as the presence of a quasi-stationary frontal system, a weak upper-level trough, sufficient moisture transportation by a low-level jet from a tropical storm landfall, strong potential and convective instability, and strong vertical wind shear. The thermodynamic characteristics and wind shear presented favorable conditions for a heavy rainfall occurrence. The early convective cells in the MCSs initiated over the coastal area, facilitated by the mesoscale boundaries of the land–sea contrast, rain–no rain regions, saturated–unsaturated soils, and steep horizontal pressure and thermal gradients. Two MCSs passed through the heavy rainfall regions during the investigation period. The first MCS initiated at 1000 UTC 26 July and had the characteristics of a supercell storm with small amounts of precipitation, the appearance of a mesocyclone with tilting storm, a rear-inflow jet at the midlevel of the storm, and fast forward propagation. The second MCS initiated over the upstream area of the first MCS at 1800 UTC 26 July and had the characteristics of a multicell storm, such as a broken areal-type squall line, slow or quasi-stationary backward propagation, heavy rainfall in a concentrated area due to the merging of the convective storms, and a stagnated cluster system. These systems merged and stagnated because their movement was blocked by the Taebaek Mountain Range, and they continued to develop because of the vertical wind shear resulting from a low-level easterly inflow.

scholarly journals Atlantic Hurricanes and Climate Change. Part II: Role of Thermodynamic Changes in Decreased Hurricane Frequency

2013 ◽  
Vol 26 (21) ◽  
pp. 8513-8528 ◽  
Author(s):  
Megan S. Mallard ◽  
Gary M. Lackmann ◽  
Anantha Aiyyer
Keyword(s):  
Case Studies ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Effect Of Temperature ◽  
Physical Processes ◽  
Thermodynamic Conditions ◽  
Atlantic Hurricanes ◽  
Reduced Activity

Abstract A method of downscaling that isolates the effect of temperature and moisture changes on tropical cyclone (TC) activity was presented in Part I of this study. By applying thermodynamic modifications to analyzed initial and boundary conditions from past TC seasons, initial disturbances and the strength of synoptic-scale vertical wind shear are preserved in future simulations. This experimental design allows comparison of TC genesis events in the same synoptic setting, but in current and future thermodynamic environments. Simulations of both an active (September 2005) and inactive (September 2009) portion of past hurricane seasons are presented. An ensemble of high-resolution simulations projects reductions in ensemble-average TC counts between 18% and 24%, consistent with previous studies. Robust decreases in TC and hurricane counts are simulated with 18- and 6-km grid lengths, for both active and inactive periods. Physical processes responsible for reduced activity are examined through comparison of monthly and spatially averaged genesis-relevant parameters, as well as case studies of development of corresponding initial disturbances in current and future thermodynamic conditions. These case studies show that reductions in TC counts are due to the presence of incipient disturbances in marginal moisture environments, where increases in the moist entropy saturation deficits in future conditions preclude genesis for some disturbances. Increased convective inhibition and reduced vertical velocity are also found in the future environment. It is concluded that a robust decrease in TC frequency can result from thermodynamic changes alone, without modification of vertical wind shear or the number of incipient disturbances.

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