scholarly journals Characteristics of Tropical Easterly Wave Pouches during Tropical Cyclone Formation

2014 ◽  
Vol 142 (2) ◽  
pp. 626-633 ◽  
Author(s):  
Zhuo Wang ◽  
Isaac Hankes
Keyword(s):  
Potential Temperature ◽  
Specific Humidity ◽  
Easterly Waves ◽  
Weather Forecasts ◽  
Warm Core ◽  
Easterly Wave ◽  
Equivalent Potential ◽  
Medium Range ◽  
Vertically Aligned ◽  
Climate Prediction Center

Abstract The pregenesis evolution of wave pouches was examined for 164 named tropical cyclones that originated from zonally propagating tropical easterly waves over the Atlantic during July–October 1989–2010 using the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) and the Climate Prediction Center (CPC) morphing technique (CMORPH) precipitation. East of 60°W, most wave pouches (~80%) form at 700 hPa first, often extending down to 850 or 925 hPa off the coast of West Africa. By contrast, the majority of the wave pouches (~68%) over the west Atlantic (west of 60°W) form at 850 or 925 hPa first. Wave pouches become more vertically aligned approaching genesis. It was also found that vorticity at 925 hPa intensifies faster than that at 600 hPa. A warm-core structure forms at the meso-β scale near the pouch center prior to genesis but is less well defined at the meso-α pouch scale. The evolution of precipitation and the low-level convergence suggests that convection begins to organize near the pouch center about 1 day prior to genesis, along with the rapid intensification of vorticity in the inner pouch region. The composites derived from ERA-Interim show that the inner pouch region has higher specific humidity and equivalent potential temperature, especially in the middle troposphere within 1 day prior to genesis.

scholarly journals CARACTERIZAÇÃO ATMOSFÉRICA QUANDO DA OCORRÊNCIA DE EVENTOS EXTREMOS DE CHUVA NA REGIÃO SUL DE MINAS GERAIS

2017 ◽  
Vol 21 ◽  
Author(s):  
Michelle Simões Reboita ◽  
Diogo Malagutti Gonçalves Marietto ◽  
Amanda Souza ◽  
Marina Barbosa
Keyword(s):  
Climate Prediction ◽  
Minas Gerais ◽  
Weather Forecasts ◽  
European Centre ◽  
Medium Range ◽  
Climate Prediction Center

O objetivo deste estudo é apresentar uma descrição das características da atmosfera que contribuíram para elevados totais de precipitação no sul de Minas Gerais e que foram precursores de dois episódios de inundação e alagamento na cidade de Itajubá: um em 16 de janeiro de 1991 e outro em 02 de janeiro de 2000. Para tanto, foram utilizados dados do Climate Prediction Center e da reanálise ERA-Interim do European Centre for Medium-Range Weather Forecasts (ECMWF). Entre os resultados, têm-se que os episódios de inundação e alagamento ocorridos na cidade de Itajubá, em ambos os anos, estiveram associados à atuação da Zona de Convergência do Atlântico Sul, que se estendia da Amazônia, passando pelo sudeste do Brasil, e chegava ao Atlântico Sul.

Four Years of Tropical ERA-40 Vorticity Maxima Tracks. Part I: Climatology and Vertical Vorticity Structure

2008 ◽  
Vol 136 (11) ◽  
pp. 4301-4319 ◽  
Author(s):  
Brandon Kerns ◽  
Kantave Greene ◽  
Edward Zipser
Keyword(s):  
Large Scale ◽  
Easterly Waves ◽  
Weather Forecasts ◽  
East Pacific ◽  
Cloud Clusters ◽  
Geographical Separation ◽  
Medium Range ◽  
Strong Gradient ◽  
Upper Level ◽  
Vorticity Structure

Abstract Using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), vorticity maxima (VM) have been manually tracked and classified as developing and nondeveloping. The VM are identified on Hovmöller plots for June–October 1998–2001, within 0°–35°N, 140°–10°W. Over 600 low-level and midlevel VM are tracked. The ERA-40 VM track climatology compares favorably with previous knowledge about easterly waves. Some new results have also been found. The VM are not equivalent to easterly waves, so it is important to distinguish between the large-scale wave and the embedded VM. Unlike waves, individual VM leaving Africa generally do not survive to cross the entire Atlantic. Unlike waves, which can cross Central America, most individual east Pacific VM originate in the east Pacific. Genesis productivity is defined as the fraction of nontropical cyclone VM that eventually develop. It reaches 50% in the eastern North Pacific (EPAC) and 30% in the Atlantic, where there is geographical separation between the locations of maximum nondeveloping and pregenesis track density. There is a strong gradient in daily genesis potential (DGP) near 10°N, associated with weaker upper-level anticyclonic vorticity equatorward of 10°N. The maximum genesis productivity is obtained north of 10°N, where the upper-anticyclonic vorticity and DGP are higher. Finally, there is no obvious distinction in VM strength between developing VM prior to genesis and nondeveloping VM. A major factor is the minimum vorticity threshold for VM as opposed to cloud clusters.

scholarly journals Predictability of a Mediterranean Tropical-Like Storm Downstream of the Extratropical Transition of Hurricane Helene (2006)

2013 ◽  
Vol 141 (6) ◽  
pp. 1943-1962 ◽  
Author(s):  
Florian P. Pantillon ◽  
Jean-Pierre Chaboureau ◽  
Patrick J. Mascart ◽  
Christine Lac
Keyword(s):  
Tropical Cyclone ◽  
Lead Time ◽  
Large Scale ◽  
Synoptic Situation ◽  
British Isles ◽  
Extratropical Transition ◽  
Ensemble Forecasts ◽  
Weather Forecasts ◽  
Warm Core ◽  
Medium Range

Abstract The extratropical transition (ET) of a tropical cyclone is known as a source of forecast uncertainty that can propagate far downstream. The present study focuses on the predictability of a Mediterranean tropical-like storm (Medicane) on 26 September 2006 downstream of the ET of Hurricane Helene from 22 to 25 September. While the development of the Medicane was missed in the deterministic forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) initialized before and during ET, it was contained in the ECMWF ensemble forecasts in more than 10% of the 50 members up to 108-h lead time. The 200 ensemble members initialized at 0000 UTC from 20 to 23 September were clustered into two nearly equiprobable scenarios after the synoptic situation over the Mediterranean. In the first and verifying scenario, Helene was steered northeastward by an upstream trough during ET and contributed to the building of a downstream ridge. A trough elongated farther downstream toward Italy and enabled the development of the Medicane in 9 of 102 members. In the second and nonverifying scenario, Helene turned southeastward during ET and the downstream ridge building was reduced. A large-scale low over the British Isles dominated the circulation in Europe and only 1 of 98 members forecasted the Medicane. The two scenarios resulted from a different phasing between Helene and the upstream trough. Sensitivity experiments performed with the Méso-NH model further revealed that initial perturbations targeted on Helene and the upstream trough were sufficient in forecasting the warm-core Medicane at 84- and 108-h lead time.

scholarly journals Formation of ice supersaturation by mesoscale gravity waves

2005 ◽  
Vol 5 (1) ◽  
pp. 67-100 ◽  
Author(s):  
P. Spichtinger ◽  
K. Gierens ◽  
A. Dörnbrack
Keyword(s):  
Gravity Waves ◽  
Internal Gravity Waves ◽  
Specific Humidity ◽  
Cirrus Cloud ◽  
Weather Forecasts ◽  
Medium Range ◽  
Formation And Evolution ◽  
The Baltic ◽  
Wave Induced ◽  
Mesoscale Simulations

Abstract. We investigate the formation and evolution of an ice-supersaturated region (ISSR) that was detected by means of an operational radiosonde sounding launched from the meteorological station of Lindenberg on 21 March 2000, 00:00 UTC. The supersaturated layer was 5 situated below the local tropopause, between 320 and 408 hPa altitude. Our investigation uses satellite imagery (METEOSAT, AVHRR) and analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). Mesoscale simulations reveal that the ISSR was formed by a temporary vertical uplift of upper tropospheric air parcels by 20 to 40 hPa in 1 to 2 h. This resulted in a significant local increase of the 10 specific humidity by the moisture transport from below. The ascent was triggered by the superposition of two internal gravity waves, a mountain wave induced by flow past the Erzgebirge and Riesengebirge south of Lindenberg, and an inertial gravity wave excited by the anticyclonically curved jet stream over the Baltic Sea. The wave-induced ISSR was rather thick with a depth of about 2 km. The wave-induced upward motion 15 causing the supersaturation also triggered the formation of a cirrus cloud. METEOSAT imagery shows that the cirrus cloud got optically thick within two hours. During this period another longer lasting thin but extended cirrus existed just beneath the tropopause. The wave-induced ISSR disappeared after about half a day in accordance with the decaying wave activity.

Potential Temperature and Potential Vorticity Inversion: Complementary Approaches

2010 ◽  
Vol 67 (12) ◽  
pp. 4001-4016 ◽  
Author(s):  
Joseph Egger ◽  
Klaus-Peter Hoinka
Keyword(s):  
North Atlantic ◽  
Potential Vorticity ◽  
Potential Temperature ◽  
Storm Track ◽  
Temperature Inversion ◽  
Weather Forecasts ◽  
The North ◽  
Potential Vorticity Inversion ◽  
Medium Range ◽  
Balanced Flow

Abstract Given the distribution of one atmospheric variable, that of nearly all others can be derived in balanced flow. In particular, potential vorticity inversion (PVI) selects potential vorticity (PV) to derive pressure, winds, and potential temperature θ. Potential temperature inversion (PTI) starts from available θ fields to derive pressure, winds, and PV. While PVI has been applied extensively, PTI has hardly been used as a research tool although the related technical steps are well known and simpler than those needed in PVI. Two idealized examples of PTI and PVI are compared. The 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) datasets are used to determine typical anomalies of PV and θ in the North Atlantic storm-track region. Statistical forms of PVI and PTI are applied to these anomalies. The inversions are equivalent but the results of PTI are generally easier to understand than those of PVI. The issues of attribution and piecewise inversion are discussed.

Interannual Variability of Monsoon Precipitation and Local Subcloud Equivalent Potential Temperature

2013 ◽  
Vol 26 (23) ◽  
pp. 9507-9527 ◽  
Author(s):  
John V. Hurley ◽  
William R. Boos
Keyword(s):  
Interannual Variability ◽  
Southern Oscillation ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Quasi Equilibrium ◽  
Equivalent Potential Temperature ◽  
Monsoon Precipitation ◽  
Relevant Variable ◽  
Near Surface ◽  
Equivalent Potential

The interannual variability of monsoon precipitation is described in the context of a convective quasi-equilibrium framework. Using two reanalysis products and two global precipitation datasets, the authors examine linear relationships between seasonal anomalies of precipitation and subcloud equivalent potential temperature (θeb) local to six monsoon regions. This approach provides a single near-surface thermodynamically relevant variable over both land and ocean, extending previous studies of interannual monsoon variability that emphasized ocean surface temperatures. After removing the variability linearly associated with an index of the El Niño–Southern Oscillation, positive monsoon precipitation anomalies are shown to be associated with enhanced θeb local to and slightly poleward of the climatological θeb maximum. The variations in continental θeb local to the monsoon precipitation maxima are mainly due to variations in subcloud specific humidity, with changes in subcloud temperature having the opposite sign. Motivated by the fact that some of these subcloud humidity anomalies occur over deserts poleward of monsoon regions, the relationship of 700-hPa flow with precipitation is examined, and enhanced precipitation in several regions is found to covary with the properties of shallow meridional circulations. The implications of these results for the understanding of monsoon interannual variability are discussed.

scholarly journals Origins of Dry Air in the Tropics and Subtropics

2007 ◽  
Vol 20 (12) ◽  
pp. 2745-2759 ◽  
Author(s):  
Piero Cau ◽  
John Methven ◽  
Brian Hoskins
Keyword(s):  
Potential Temperature ◽  
Lower Troposphere ◽  
Transport Processes ◽  
Air Masses ◽  
Weather Forecasts ◽  
Dry Air ◽  
Medium Range ◽  
Net Pressure ◽  
The Tropics ◽  
The Relationship

Abstract The humidity in the dry regions of the tropical and subtropical troposphere has a major impact on the ability of the atmosphere to radiate heat to space. The water vapor content in these regions is determined by their “origins,” here defined as the last condensation event following air masses. Trajectory simulations are used to investigate such origins using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) data for January 1993. It is shown that 96% of air parcels experience condensation within 24 days and most of the remaining 4% originate in the stratosphere. Dry air masses are shown to experience a net pressure increase since last condensation, which is uniform with latitude, while the median time taken for descent is 5 days into the subtropics but exceeds 16 days into the equatorial lower troposphere. The associated rate of decrease in potential temperature is consistent with radiative cooling. The relationship between the drier regions in the Tropics and subtropics and the geographical localization of their origin is investigated. Four transport processes are identified to explain these relationships.

scholarly journals Convectively Coupled Kelvin Waves and Tropical Cyclogenesis in a Semi-Lagrangian Framework

2016 ◽  
Vol 144 (11) ◽  
pp. 4131-4139 ◽  
Author(s):  
Carl J. Schreck
Keyword(s):  
North Atlantic ◽  
Phase Speed ◽  
Kelvin Waves ◽  
Tropical Cyclogenesis ◽  
Kelvin Wave ◽  
Easterly Waves ◽  
The North ◽  
Lagrangian Framework ◽  
Easterly Wave ◽  
Vertically Aligned

Abstract This study examines how convectively coupled Kelvin waves interact with the semi-Lagrangian circulation of easterly waves to modulate tropical cyclogenesis. Recent studies have shown that fewer tropical cyclones form in the three days before passage of the Kelvin wave’s peak convection and more develop in the three days thereafter. Separately, other studies have identified the recirculation of moisture and vorticity within easterly waves using a semi-Lagrangian frame of reference. That framework is achieved by subtracting the easterly wave phase speed from the earth-relative winds. This study combines these recent findings by testing whether the equatorial westerlies from Kelvin waves can help close the semi-Lagrangian circulation. Past studies have shown that Kelvin waves tilt westward with height in the troposphere such that equatorial westerlies build upward from the surface in the days following the convective peak. This study shows that the easterly wave’s semi-Lagrangian closed circulation grows upward as it intersects the Kelvin wave’s westward tilt. The Kelvin wave’s westerly anomalies reach 500 hPa about three days after the convection has passed, which establishes the deep, vertically aligned easterly wave vortex necessary for tropical cyclogenesis. This study focuses on the eastern Pacific, but similar results are found for the North Atlantic. In other basins, the Kelvin wave accentuates the westerlies from the Madden–Julian oscillation and/or the monsoon trough. Given that Kelvin waves often last weeks and circumnavigate the globe, these results may advance long-range tropical cyclogenesis forecasting.

The Relative Contributions of Temperature and Moisture to Heat Stress Changes under Warming

2021 ◽  
Vol 34 (3) ◽  
pp. 901-917
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
Heat Stress ◽  
Relative Humidity ◽  
Climate Model ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Temperature Changes ◽  
Equivalent Potential ◽  
Stress Changes ◽  
Intercomparison Project ◽  
Health And Mortality

AbstractIncreases in the severity of heat stress extremes are potentially one of the most impactful consequences of climate change, affecting human comfort, productivity, health, and mortality in many places on Earth. Heat stress results from a combination of elevated temperature and humidity, but the relative contributions of each of these to heat stress changes have yet to be quantified. Here, conditions for the baseline specific humidity are derived for when specific humidity or temperature dominates heat stress changes, as measured using the equivalent potential temperature (θE). Separate conditions are derived over ocean and over land, in addition to a condition for when relative humidity changes make a larger contribution than the Clausius–Clapeyron response at fixed relative humidity. These conditions are used to interpret the θE responses in transient warming simulations with an ensemble of models participating in phase 6 of the Climate Model Intercomparison Project. The regional pattern of θE changes is shown to be largely determined by the pattern of specific humidity changes, with the pattern of temperature changes playing a secondary role. This holds whether considering changes in seasonal-mean θE or in extreme (98th-percentile) θE events, and uncertainty in the response of specific humidity to warming is shown to be the leading source of uncertainty in the θE response at most land locations. Finally, analysis of ERA5 data demonstrates that the pattern of observed θE changes is also well explained by the pattern of specific humidity changes. These results demonstrate that understanding regional changes in specific humidity is largely sufficient for understanding regional changes in heat stress.

scholarly journals Impact Study of FY-3B MWRI Data Assimilation in WRFDA

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 497
Author(s):  
Chun Yang ◽  
Lijian Zhu ◽  
Jinzhong Min
Keyword(s):  
Wind Speed ◽  
Data Assimilation ◽  
Three Dimensional ◽  
Analysis Data ◽  
Specific Humidity ◽  
Sea Level Pressure ◽  
Weather Forecasts ◽  
Warm Core ◽  
Radiance Data ◽  
The Impact

In the first attempt to configure the Fengyun-3B satellite’s Microwave Radiation Imager (MWRI) radiance data in the Weather Research Forecast (WRF) model’s Data Assimilation system (WRFDA), the impact of MWRI data assimilation on the analysis and forecast of Typhoon Son-Tinh in 2012 was evaluated with WRFDA’s three-dimensional variational (3DVAR) data-assimilation scheme. Compared to a benchmark experiment with no MWRI data, assimilating MWRI radiances improved the analyses of typhoon central sea level pressure (CSLP), warm core structure, and wind speed. Moreover, verified with European Center for Medium-Range Weather Forecasts (ECMWF) analysis data, significant improvements in model variable forecast, such as geopotential height and specific humidity, were produced. Substantial error reductions in track, CSLP, and maximum-wind-speed forecasts with MWRI assimilation was also obtained from analysis time to 48 h forecast.

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