scholarly journals Sensitivity of Tropical Cyclones to Parameterized Convection in the NASA GEOS-5 Model

2015 ◽  
Vol 28 (2) ◽  
pp. 551-573 ◽  
Author(s):  
Young-Kwon Lim ◽  
Siegfried D. Schubert ◽  
Oreste Reale ◽  
Myong-In Lee ◽  
Andrea M. Molod ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Moisture Flux ◽  
Moist Convection ◽  
Horizontal Structure ◽  
Maximum Wind ◽  
The North ◽  
Control Configuration ◽  
The Impact

Abstract The sensitivity of tropical cyclones (TCs) to changes in parameterized convection is investigated to improve the simulation of TCs in the North Atlantic. Specifically, the impact of reducing the influence of the Relaxed Arakawa–Schubert (RAS) scheme-based parameterized convection is explored using the Goddard Earth Observing System version 5 (GEOS-5) model at 0.25° horizontal grid spacing. The years 2005 and 2006, characterized by very active and inactive hurricane seasons, respectively, are selected for simulation. A reduction in parameterized deep convection results in an increase in TC activity (e.g., TC number and longer life cycle) to more realistic levels compared to the baseline control configuration. The vertical and horizontal structure of the strongest simulated hurricane shows the maximum wind speed greater than 60 m s−1 and the minimum sea level pressure reaching ~940 mb, which are never achieved by the control configuration. The radius of the maximum wind of ~50 km, the location of the warm core exceeding 10°C, and the horizontal compactness of the hurricane center are all quite realistic without any negatively affecting the atmospheric mean state. This study reveals that an increase in the threshold of minimum entrainment suppresses parameterized deep convection by entraining more dry air into the typical plume. This leads to cooling and drying at the mid to upper troposphere, along with the positive latent heat flux and moistening in the lower troposphere. The resulting increase in conditional instability provides an environment that is more conducive to TC vortex development and upward moisture flux convergence by dynamically resolved moist convection, thereby increasing TC activity.

scholarly journals Seasonal Evolution of Aleutian Low Pressure Systems: Implications for the North Pacific Subpolar Circulation*

2009 ◽  
Vol 39 (6) ◽  
pp. 1317-1339 ◽  
Author(s):  
Robert S. Pickart ◽  
Alison M. Macdonald ◽  
G. W. K. Moore ◽  
Ian A. Renfrew ◽  
John E. Walsh ◽  
...  
Keyword(s):  
North Pacific ◽  
Lower Troposphere ◽  
Gulf Of Alaska ◽  
Low Pressure ◽  
Aleutian Low ◽  
The North ◽  
Early Fall ◽  
The Impact ◽  
The North Pacific ◽  
Low Pressure Systems

Abstract The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres.

scholarly journals Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

2016 ◽  
Author(s):  
M. Venkat Ratnam ◽  
S. Ravindra Babu ◽  
S. S. Das ◽  
Ghouse Basha ◽  
B. V. Krishnamurthy ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Lower Stratosphere ◽  
North Indian Ocean ◽  
Satellite Observations ◽  
Upper Troposphere ◽  
North West ◽  
The North ◽  
The Impact

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.

scholarly journals Land–atmosphere interactions in the tropics

2019 ◽  
Author(s):  
Pierre Gentine ◽  
Adam Massmann ◽  
Benjamin R. Lintner ◽  
Sayed Hamed Alemohammad ◽  
Rong Fu ◽  
...  
Keyword(s):  
Land Surface ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Surface Fluxes ◽  
Surface Radiation ◽  
Spatial And Temporal Scales ◽  
Wide Range ◽  
Shallow Clouds ◽  
The Tropics ◽  
The Impact

Abstract. The continental tropics play a leading role in the terrestrial water and carbon cycles. Land–atmosphere interactions are integral in the regulation of surface energy, water and carbon fluxes across multiple spatial and temporal scales over tropical continents. We review here some of the important characteristics of tropical continental climates and how land–atmosphere interactions regulate them. Along with a wide range of climates, the tropics manifest a diverse array of land–atmosphere interactions. Broadly speaking, in tropical rainforests, light and energy are typically more limiting than precipitation and water supply for photosynthesis and evapotranspiration; whereas in savanna and semi-arid regions water is the critical regulator of surface fluxes and land–atmosphere interactions. We discuss the impact of the land surface, how it affects shallow clouds and how these clouds can feedback to the surface by modulating surface radiation. Some results from recent research suggest that shallow clouds may be especially critical to land–atmosphere interactions as these regulate the energy budget and moisture transport to the lower troposphere, which in turn affects deep convection. On the other hand, the impact of land surface conditions on deep convection appear to occur over larger, non-local, scales and might be critically affected by transitional regions between the climatologically dry and wet tropics.

scholarly journals Can the Impact of Aerosols on Deep Convection be Isolated from Meteorological Effects in Atmospheric Observations?

2018 ◽  
Vol 75 (10) ◽  
pp. 3347-3363 ◽  
Author(s):  
Wojciech W. Grabowski
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Phase Iii ◽  
Moist Convection ◽  
Atmospheric Measurements ◽  
The Impact ◽  
Meteorological Effects

Influence of pollution on dynamics of deep convection continues to be a controversial topic. Arguably, only carefully designed numerical simulations can clearly separate the impact of aerosols from the effects of meteorological factors that affect moist convection. This paper argues that such a separation is virtually impossible using observations because of the insufficient accuracy of atmospheric measurements and the fundamental nature of the interaction between deep convection and its environment. To support this conjecture, results from numerical simulations are presented that apply modeling methodology previously developed by the author. The simulations consider small modifications, difficult to detect in observations, of the initial sounding, surface fluxes, and large-scale forcing tendencies. All these represent variations of meteorological conditions that affect deep convective dynamics independently of aerosols. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere–Atmosphere (LBA) field project in Amazonia. The simulated observable macroscopic changes of convection, such as the surface precipitation and upper-tropospheric cloudiness, are similar to or larger than those resulting from changes of cloud condensation nuclei from pristine to polluted conditions studied previously using the same modeling case. Observations from Phase III of the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) are also used to support the argument concerning the impact of the large-scale forcing. The simulations suggest that the aerosol impacts on dynamics of deep convection cannot be isolated from meteorological effects, at least for the daytime development of unorganized deep convection considered in this study.

Detecting drought conditions related to vegetation at west continental Europe based on variations from the North and Caspian Seas

2021 ◽  
Author(s):  
Bolin Xu ◽  
Qing He ◽  
Kwok Pan Chun ◽  
Julian Klaus ◽  
Rémy Schoppach ◽  
...  
Keyword(s):  
North Sea ◽  
Vegetation Index ◽  
Lower Troposphere ◽  
Principal Component ◽  
Positive Phase ◽  
Vegetation Patterns ◽  
Limited Region ◽  
The North ◽  
The North Sea ◽  
The Impact

<p>Teleconnections relate regional pressure patterns to local climate anomalies, influencing the variation of vegetation patterns. Over west continental Europe, droughts have been widely investigated with persistent low-frequency atmospheric circulation patterns (e.g. the North Atlantic Oscillation, NAO) with the centers over the Atlantic based on the 500mb height anomalies of the Northern Hemisphere. However, the effects of teleconnection patterns with the centers of active variability over the North and Caspian Seas is largely unexplored for droughts related to vegetation patterns. In this study, we explored the impact of the North Sea-Caspian Pattern (NCP) on regional ecohydrologic conditions in the Greater Region of Luxembourg in Western Europe. Using a Principal Component Analysis (PCA), we first decomposed the annual Normalized Difference Vegetation Index (NDVI) from the Global Inventory Monitoring and Modeling System (GIMMS) between 1981 and 2015. In the first PCA component, a distinctive greening trend of NDVI is detected since the late 1980s. However, the corresponding station observations and the ERA5 reanalysis data show that the region in west continental Europe became increasingly drier based on the difference between precipitation and evaporation. We explain the above paradoxical greening but drying patterns by the mechanism of NCP over the region. During the positive phase of NCP, the high pressure over the North Sea weakens circulation over the region and leads to warmer conditions in west continental Europe. These conditions are good for vegetation growth because the region was mainly energy-limited during the observed period at the annual scale based on a Budyko analysis. However, the positive phase of NCP also promotes divergent conditions at the lower troposphere and it reduces moisture flux over the region. In the Budyko space, the persistent positive phase of NCP would lead the energy-limited region to be water-limited. As the positive phase of NCP is expected to be more frequent along with the increasing global temperatures, the region may start to experience increasing water stress on vegetation. These results suggest that unforeseen droughts related to vegetation may be emerging in the region. New drought monitoring and management measures related to vegetation should be developed at west continental Europe, especially during the positive phase of NCP.</p>

scholarly journals Wind-driven transport of fresh shelf water into the upper 30 m of the Labrador Sea

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1247-1264 ◽  
Author(s):  
Lena M. Schulze Chretien ◽  
Eleanor Frajka-Williams
Keyword(s):  
North Atlantic ◽  
Surface Waters ◽  
Deep Convection ◽  
Greenland Ice Sheet ◽  
Ocean Model ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Labrador Sea ◽  
The North ◽  
The Impact

Abstract. The Labrador Sea is one of a small number of deep convection sites in the North Atlantic that contribute to the meridional overturning circulation. Buoyancy is lost from surface waters during winter, allowing the formation of dense deep water. During the last few decades, mass loss from the Greenland ice sheet has accelerated, releasing freshwater into the high-latitude North Atlantic. This and the enhanced Arctic freshwater export in recent years have the potential to add buoyancy to surface waters, slowing or suppressing convection in the Labrador Sea. However, the impact of freshwater on convection is dependent on whether or not it can escape the shallow, topographically trapped boundary currents encircling the Labrador Sea. Previous studies have estimated the transport of freshwater into the central Labrador Sea by focusing on the role of eddies. Here, we use a Lagrangian approach by tracking particles in a global, eddy-permitting (1/12∘) ocean model to examine where and when freshwater in the surface 30 m enters the Labrador Sea basin. We find that 60 % of the total freshwater in the top 100 m enters the basin in the top 30 m along the eastern side. The year-to-year variability in freshwater transport from the shelves to the central Labrador Sea, as found by the model trajectories in the top 30 m, is dominated by wind-driven Ekman transport rather than eddies transporting freshwater into the basin along the northeast.

scholarly journals Effect of deep convection on the TTL composition over the Southwest Indian Ocean during austral summer

2020 ◽  
Author(s):  
Stephanie Evan ◽  
Jerome Brioude ◽  
Karen Rosenlof ◽  
Sean M. Davis ◽  
Hölger Vömel ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Austral Summer ◽  
Active Regions ◽  
Lagrangian Model ◽  
Southwest Indian Ocean ◽  
Tropopause Region ◽  
The Impact

Abstract. Balloon-borne measurements of CFH water vapor, ozone and temperature and water vapor lidar measurements from the Maïdo Observatory at Réunion Island in the Southwest Indian Ocean (SWIO) were used to study tropical cyclones' influence on TTL composition. The balloon launches were specifically planned using a Lagrangian model and METEOSAT 7 infrared images to sample the convective outflow from Tropical Storm (TS) Corentin on 25 January 2016 and Tropical Cyclone (TC) Enawo on 3 March 2017. Comparing CFH profile to MLS monthly climatologies, water vapor anomalies were identified. Positive anomalies of water vapor and temperature, and negative anomalies of ozone between 12 and 15 km in altitude (247 to 121 hPa) originated from convectively active regions of TS Corentin and TC Enawo, one day before the planned balloon launches, according to the Lagrangian trajectories. Near the tropopause region, air masses on 25 January 2016 were anomalously dry around 100 hPa and were traced back to TS Corentin active convective region where cirrus clouds and deep convective clouds may have dried the layer. An anomalously wet layer around 68 hPa was traced back to the South East IO where a monthly water vapor anomaly of 0.5 ppbv was observed. In contrast, no water vapor anomaly was found near or above the tropopause region on 3 March 2017 over Maïdo as the tropopause region was not downwind of TC Enawo. This study compares and contrasts the impact of two tropical cyclones on the humidification of the TTL over the Southwest Indian Ocean.

scholarly journals Uncertainties in atmospheric chemistry modelling due to convection parameterisations and subsequent scavenging

2010 ◽  
Vol 10 (4) ◽  
pp. 1931-1951 ◽  
Author(s):  
H. Tost ◽  
M. G. Lawrence ◽  
C. Brühl ◽  
P. Jöckel ◽  
◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Model Simulation ◽  
Chemical Reactivity ◽  
Deep Convection ◽  
Trace Gases ◽  
Convective Transport ◽  
Moist Convection ◽  
Tracer Transport ◽  
Convection Schemes ◽  
The Impact

Abstract. Moist convection in global modelling contributes significantly to the transport of energy, momentum, water and trace gases and aerosols within the troposphere. Since convective clouds are on a scale too small to be resolved in a global model their effects have to be parameterised. However, the whole process of moist convection and especially its parameterisations are associated with uncertainties. In contrast to previous studies on the impact of convection on trace gases, which had commonly neglected the convective transport for some or all compounds, we investigate this issue by examining simulations with five different convection schemes. This permits an uncertainty analysis due to the process formulation, without the inconsistencies inherent in entirely neglecting deep convection or convective tracer transport for one or more tracers. Both the simulated mass fluxes and tracer distributions are analysed. Investigating the distributions of compounds with different characteristics, e.g., lifetime, chemical reactivity, solubility and source distributions, some differences can be attributed directly to the transport of these compounds, whereas others are more related to indirect effects, such as the transport of precursors, chemical reactivity in certain regions, and sink processes. The model simulation data are compared with the average regional profiles of several measurement campaigns, and in detail with two campaigns in fall and winter 2005 in Suriname and Australia, respectively. The shorter-lived a compound is, the larger the differences and consequently the uncertainty due to the convection parameterisation are, as long as it is not completely controlled by local production that is independent of convection and its impacts (e.g. water vapour changes). Whereas for long-lived compounds like CO or O3 the mean differences between the simulations are less than 25%), differences for short-lived compounds reach up to ±100% with different convection schemes. A rating of an overall "best" performing scheme is difficult, since the optimal performance depends on the region and compound.

The moisture budget of tropical cyclones: large scale environmental constraints and sensitivity to model horizontal resolution

2020 ◽  
Author(s):  
Benoit Vanniere ◽  
Malcolm Roberts ◽  
Pier Luigi Vidale ◽  
Kevin Hodges ◽  
Marie-Estelle Demory
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Climate Models ◽  
Potential Temperature ◽  
Large Change ◽  
Moisture Flux ◽  
Horizontal Resolution ◽  
Moisture Budget ◽  
High Resolution Models ◽  
The Impact

<p>Previous studies have shown that, the number, intensity and structure of simulated tropical cyclones (TC) in climate models get closer to the observations as the horizontal resolution is increased. However, the sensitivity of tropical cyclone precipitation and moisture budget to changes in resolution has received less attention. In this study, we use the five-model ensemble from project PRIMAVERA/HighResMIP to investigate the systematic changes associated with the water budget of tropical cyclones in a range of horizontal resolutions from 1º to 0.25º. Our results show that despite a large change in the distribution of TC intensity with resolution, the distribution of precipitation per TC does not change significantly. This result is explained by the large scale balance which characterises the moisture budget of TCs, i.e. radii of ~15º a scale that low and high resolution models represent equally well. The wind profile is found to converge between low and high resolutions for radii > 5º, resulting in a moisture flux convergence into the TC with similar magnitude at low and high resolutions. In contrast to precipitation per TC, the larger TC intensity at higher resolution is explained by the larger surface latent heat flux near the center of the storm, which leads to an increase in equivalent potential temperature and warmer core anomalies, despite representing a negligible contribution to the moisture budget. We discuss the complication arising from the choice of the tracking algorithm when assessing the impact of model resolution and the implications of such a constraint on the TC moisture budget in the context of climate change.</p>

scholarly journals Tropical Cyclones in the UPSCALE Ensemble of High-Resolution Global Climate Models*

2015 ◽  
Vol 28 (2) ◽  
pp. 574-596 ◽  
Author(s):  
Malcolm J. Roberts ◽  
Pier Luigi Vidale ◽  
Matthew S. Mizielinski ◽  
Marie-Estelle Demory ◽  
Reinhard Schiemann ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
Global Climate ◽  
Future Climate ◽  
Model Resolution ◽  
Central Pacific ◽  
The North ◽  
The Future ◽  
The North Atlantic ◽  
The Impact

Abstract The U.K. on Partnership for Advanced Computing in Europe (PRACE) Weather-Resolving Simulations of Climate for Global Environmental Risk (UPSCALE) project, using PRACE resources, constructed and ran an ensemble of atmosphere-only global climate model simulations, using the Met Office Unified Model Global Atmosphere 3 (GA3) configuration. Each simulation is 27 years in length for both the present climate and an end-of-century future climate, at resolutions of N96 (130 km), N216 (60 km), and N512 (25 km), in order to study the impact of model resolution on high-impact climate features such as tropical cyclones. Increased model resolution is found to improve the simulated frequency of explicitly tracked tropical cyclones, and correlations of interannual variability in the North Atlantic and northwestern Pacific lie between 0.6 and 0.75. Improvements in the deficit of genesis in the eastern North Atlantic as resolution increases appear to be related to the representation of African easterly waves and the African easterly jet. However, the intensity of the modeled tropical cyclones as measured by 10-m wind speed remains weak, and there is no indication of convergence over this range of resolutions. In the future climate ensemble, there is a reduction of 50% in the frequency of Southern Hemisphere tropical cyclones, whereas in the Northern Hemisphere there is a reduction in the North Atlantic and a shift in the Pacific with peak intensities becoming more common in the central Pacific. There is also a change in tropical cyclone intensities, with the future climate having fewer weak storms and proportionally more strong storms.

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