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 Comparison between the Large-Scale Environments of Moderate and Intense Precipitating Systems in the Mediterranean Region

2009 ◽  
Vol 137 (11) ◽  
pp. 3933-3959 ◽  
Author(s):  
Beatriz M. Funatsu ◽  
Chantal Claud ◽  
Jean-Pierre Chaboureau
Keyword(s):  
Mediterranean Region ◽  
Large Scale ◽  
Deep Convection ◽  
Extreme Rainfall ◽  
Convective Precipitation ◽  
Target Area ◽  
Weather Forecasts ◽  
Microwave Sounding ◽  
The Mediterranean ◽  
Upper Level

Abstract A characterization of the large-scale environment associated with precipitating systems in the Mediterranean region, based mainly on NOAA-16 Advanced Microwave Sounding Unit (AMSU) observations from 2001 to 2007, is presented. Channels 5, 7, and 8 of AMSU-A are used to identify upper-level features, while a simple and tractable method, based on combinations of channels 3–5 of AMSU-B and insensitive to land–sea contrast, was used to identify precipitation. Rain occurrence is widespread over the Mediterranean in wintertime while reduced or short lived in the eastern part of the basin in summer. The location of convective precipitation shifts from mostly over land from April to August, to mostly over the sea from September to December. A composite analysis depicting large-scale conditions, for cases of either rain alone or extensive areas of deep convection, is performed for selected locations where the occurrence of intense rainfall was found to be important. In both cases, an upper-level trough is seen to the west of the target area, but for extreme rainfall the trough is narrower and has larger amplitude in all seasons. In general, these troughs are also deeper for extreme rainfall. Based on the European Centre for Medium-Range Weather Forecasts operational analyses, it was found that sea surface temperature anomalies composites for extreme rainfall are often about 1 K warmer, compared to nonconvective precipitation conditions, in the vicinity of the affected area, and the wind speed at 850 hPa is also stronger and usually coming from the sea.

scholarly journals An update on global atmospheric ice estimates from satellite observations and reanalyses

2018 ◽  
Author(s):  
David Ian Duncan ◽  
Patrick Eriksson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Principal Component ◽  
Diurnal Variability ◽  
Weather Forecasts ◽  
Earth Observing System ◽  
Current State ◽  
Medium Range ◽  
Ice Water ◽  
Modern Era

Abstract. This study assesses the global distribution of mean atmospheric ice mass from current state-of-the-art estimates and its variability on daily and seasonal timescales. Ice water path (IWP) retrievals from active and passive satellite platforms are compared and analysed against estimates from two reanalysis datasets, ERA5 (European Centre for Medium-range Weather Forecasts Reanalysis 5) and MERRA-2 (Modern-era Retrospective Reanalysis for Research and Applications 2). Large discrepancies in IWP exist between the satellite datasets themselves, making validation of the model results problematic and indicating that progress towards consensus on the distribution of atmospheric ice has been limited. Comparing the datasets, zonal means of IWP exhibit similar shapes but differing magnitudes. Diurnal analysis centred on A-Train overpasses shows homologous structures in some regions, but the degree and sign of the variability varies widely; the reanalyses exhibit noisier and higher amplitude diurnal variability than borne out by the satellite estimates. Spatial structures governed by the atmospheric general circulation are fairly consistent across the datasets, as principal component analysis shows that the patterns of seasonal variability line up well between the datasets but disagree in severity. These results underscore the limitations of the current Earth observing system with respect to atmospheric ice, as the level of consensus between observations is mixed. The large-scale variability of IWP is relatively consistent, whereas disagreements on diurnal variability and global means point to varying microphysical assumptions in retrievals and models alike that seem to underlie the biggest differences.

scholarly journals How much snow falls in the world's mountains? A first look at mountain snowfall estimates in A-train observations and reanalyses

2020 ◽  
Vol 14 (9) ◽  
pp. 3195-3207
Author(s):  
Anne Sophie Daloz ◽  
Marian Mateling ◽  
Tristan L'Ecuyer ◽  
Mark Kulie ◽  
Norm B. Wood ◽  
...  
Keyword(s):  
Large Scale ◽  
Critical Factor ◽  
Weather Forecasts ◽  
Cloud Radar ◽  
Regional Trends ◽  
Medium Range ◽  
America South ◽  
Alpine Environments ◽  
Modern Era ◽  
Factor Governing

Abstract. CloudSat estimates that 1773 km3 of snow falls, on average, each year over the world's mountains. This amounts to 5 % of the global snowfall accumulations. This study synthetizes mountain snowfall estimates over the four continents containing mountains (Eurasia, North America, South America and Africa), comparing snowfall estimates from a new satellite cloud-radar-based dataset to those from four widely used reanalyses: Modern-Era Retrospective analysis for Research and Applications (MERRA), MERRA-2, Japanese 55-year Reanalysis (JRA-55), and European Center for Medium-Range Weather Forecasts Re-Analysis (ERA-Interim). Globally, the fraction of snow that falls in the world's mountains is very similar between all these independent datasets (4 %–5 %), providing confidence in this estimate. The fraction of snow that falls in the mountains compared to the continent as a whole is also very similar between the different datasets. However, the total of snow that falls globally and over each continent – the critical factor governing freshwater availability in these regions – varies widely between datasets. The consensus in fractions and the dissimilarities in magnitude could indicate that large-scale forcings may be similar in the five datasets, while local orographic enhancements at smaller scales may not be captured. This may have significant implications for our ability to diagnose regional trends in snowfall and its impacts on snowpack in rapidly evolving alpine environments.

scholarly journals Downscaling Dinâmico sobre o Nordeste do Brasil Utilizando um Modelo Climático Regional: Impacto de Diferentes Parametrizações na Precipitação Simulada (Dynamic Downscaling over Northeast Brazil Using a Regional Climate Model: Impact of Different ...)

2013 ◽  
Vol 6 (4) ◽  
pp. 995 ◽  
Author(s):  
Vanessa De Almeida Dantas ◽  
Ana Cleide Bezerra Amorim ◽  
Micejane Da Silva Costa ◽  
Cláudio Moisés Santos e Silva
Keyword(s):  
Large Scale ◽  
Tropical Rainfall Measuring Mission ◽  
Rainfall Simulation ◽  
Cumulus Parameterization ◽  
Scale Model ◽  
Dynamic Downscaling ◽  
Tropical Rainfall ◽  
Weather Forecasts ◽  
European Centre ◽  
Medium Range

Estudos utilizando modelos regionais na realização de downscaling dinâmico tem se mostrado adequado para reproduzir a escala local de uma região. Neste sentido, o presente estudo teve como objetivo analisar a sensibilidade de simulação da precipitação para o ano de 2009 na região do Nordeste Brasileiro (NEB) utilizando três esquemas de parametrização cumulus disponíveis no modelo RegCM4, a saber: Anthes Kuo (Kuo), Grell com fechamento Fristish Chappell (GFC) e MIT-Emmanuel (EM). Como condição inicial e de contorno de grande escala foram usadas informações do modelo European Centre for Medium-Range Weather Forecasts (ECMWF), especificamente o produto ERA_interim. Dados do projeto Tropical Rainfall Measuring Mission (TRMM) foram usados para a avaliação da precipitação simulada. Testes e parâmetros estatísticos foram usados como métrica na avaliação das simulações. Verificou-se que o modelo consegue representar de forma adequada a precipitação quando comparada aos dados do TRMM. Os experimentos que mais se aproximaram das observações foram GFC e EM. O RegCM4 subestimou a precipitação no NEB no início de março e superestimando em meados de julho. Entretanto, é possível afirmar que o modelo é capaz de reproduzir bem a variabilidade do clima, na região do NEB, após alguns ajustes utilizando diferentes tipos parametrizações para os trópicos. ABSTRACT Studies using regional models in performing dynamic downscaling have been adequate to reproduce the local scale of a region. In this sense, the present study aimed to analyze the sensitivity of rainfall simulation for the year 2009 in the Brazilian Northeast (NEB) using three cumulus parameterization schemes available in RegCM4 model, namely: Anthes Kuo (Kuo) Grell closure Fristish Chappell (GFC), and MIT-Emmanuel (EM). As a condition of initial and boundary large scale model information were used European Centre for Medium-Range Weather Forecasts (ECMWF), specifically the product ERA_interim. Project data Tropical Rainfall Measuring Mission (TRMM) were used for the evaluation of simulated rainfall. Testing and statistical parameters were used as a metric in evaluating simulations. It was found that the model can adequately represent the precipitation compared with data from TRMM. The experiments that came closer to the observations were GFC and EM. The RegCM4 underestimated precipitation in the NEB in early March and overestimating in mid-July. However, we can say that the model is able to reproduce well the climate variability in the region of the NEB, after some adjustments using different parameterizations for the tropics. Keywords: RegCM4, Kuo, Grell, Emanuel

scholarly journals Does the ECMWF IFS Convection Parameterization with Stochastic Physics Correctly Reproduce Relationships between Convection and the Large-Scale State?

2015 ◽  
Vol 72 (1) ◽  
pp. 236-242 ◽  
Author(s):  
Peter A. G. Watson ◽  
H. M. Christensen ◽  
T. N. Palmer
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Weather Forecast ◽  
Tropical Convection ◽  
Short Term ◽  
Vertical Temperature Profile ◽  
Weather Forecasts ◽  
Medium Range ◽  
Convection Parameterization ◽  
Stochastic Physics

Abstract Important questions concerning parameterization of tropical convection are how should subgrid-scale variability be represented and which large-scale variables should be used in the parameterizations? Here the statistics of observational data in Darwin, Australia, are compared with those of short-term forecasts of convection made by the European Centre for Medium-Range Weather Forecasts Integrated Forecast System. The forecasts use multiplicative-noise stochastic physics (MNSP) that has led to many improvements in weather forecast skill. However, doubts have recently been raised about whether MNSP is consistent with observations of tropical convection. It is shown that the model can reproduce the variability of convection intensity for a given large-scale state, both with and without MNSP. Therefore MNSP is not inconsistent with observations, and much of the modeled variability arises from nonlinearity of the deterministic part of the convection scheme. It is also shown that the model can reproduce the lack of correlation between convection intensity and large-scale CAPE and an entraining CAPE, even though the convection parameterization assumes that deep convection is more intense when the vertical temperature profile is more unstable, with entrainment taken into account. Relationships between convection and large-scale convective inhibition and vertical velocity are also correctly captured.

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 Observations of a Nondeveloping Tropical Disturbance in the Western North Pacific during TCS-08 (2008)

2015 ◽  
Vol 143 (7) ◽  
pp. 2459-2484 ◽  
Author(s):  
Andrew B. Penny ◽  
Patrick A. Harr ◽  
Michael M. Bell
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Low Level ◽  
The North ◽  
Cloud Clusters ◽  
Potential Formation ◽  
Shearing Deformation ◽  
Upper Level

Abstract Large uncertainty still remains in determining whether a tropical cloud cluster will develop into a tropical cyclone. During The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC)/Tropical Cyclone Structure-2008 (TCS-08) field experiment, over 50 tropical cloud clusters were monitored for development, but only 4 developed into a tropical cyclone. One nondeveloping tropical disturbance (TCS025) was closely observed for potential formation during five aircraft research missions, which provided an unprecedented set of observations pertaining to the large-scale and convective environments of a nondeveloping system. The TCS025 disturbance was comprised of episodic convection that occurred in relation to the diurnal cycle along the eastern extent of a broad low-level trough. The upper-level environment was dominated by two cyclonic cells in the tropical upper-tropospheric trough (TUTT) north of the low-level trough in which the TCS025 circulation was embedded. An in-depth examination of in situ observations revealed that the nondeveloping circulation was asymmetric and vertically misaligned, which led to larger system-relative flow on the mesoscale. Persistent environmental vertical wind shear and horizontal shearing deformation near the circulation kept the system from becoming better organized and appears to have allowed low equivalent potential temperature () air originating from one of the TUTT cells to the north (upshear) to impact the thermodynamic environment of TCS025. This in turn weakened subsequent convection that might otherwise have improved alignment and contributed to the transition of TCS025 to a tropical cyclone.

scholarly journals Tracking and Mean Structure of Easterly Waves over the Intra-Americas Sea

2010 ◽  
Vol 23 (18) ◽  
pp. 4823-4840 ◽  
Author(s):  
Yolande L. Serra ◽  
George N. Kiladis ◽  
Kevin I. Hodges
Keyword(s):  
Large Scale ◽  
Zonal Flow ◽  
Leeward Side ◽  
Easterly Waves ◽  
East Pacific ◽  
Sierra Madre ◽  
Mean Structure ◽  
The Caribbean ◽  
The Waves ◽  
Model Topography

Abstract Easterly waves (EWs) are prominent features of the intertropical convergence zone (ITCZ), found in both the Atlantic and Pacific during the Northern Hemisphere summer and fall, where they commonly serve as precursors to hurricanes over both basins. A large proportion of Atlantic EWs are known to form over Africa, but the origin of EWs over the Caribbean and east Pacific in particular has not been established in detail. In this study reanalyses are used to examine the coherence of the large-scale wave signatures and to obtain track statistics and energy conversion terms for EWs across this region. Regression analysis demonstrates that some EW kinematic structures readily propagate between the Atlantic and east Pacific, with the highest correlations observed across Costa Rica and Panama. Track statistics are consistent with this analysis and suggest that some individual waves are maintained as they pass from the Atlantic into the east Pacific, whereas others are generated locally in the Caribbean and east Pacific. Vortex anomalies associated with the waves are observed on the leeward side of the Sierra Madre, propagating northwestward along the coast, consistent with previous modeling studies of the interactions between zonal flow and EWs with model topography similar to the Sierra Madre. An energetics analysis additionally indicates that the Caribbean low-level jet and its extension into the east Pacific—known as the Papagayo jet—are a source of energy for EWs in the region. Two case studies support these statistics, as well as demonstrate the modulation of EW track and storm development location by the MJO.

scholarly journals The representation of winds in the lower troposphere in ECMWF forecasts and reanalyses during the EUREC4A field campaign

2022 ◽  
Author(s):  
Alessandro Carlo Maria Savazzi ◽  
Louise Nuijens ◽  
Irina Sandu ◽  
Geet George ◽  
Peter Bechtold
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Lower Troposphere ◽  
Meridional Wind ◽  
Forecast Errors ◽  
Strong Wind ◽  
Field Campaign ◽  
Weather Forecasts ◽  
Medium Range ◽  
Convective Momentum Transport

Abstract. The characterization of systematic forecast errors in lower-tropospheric winds over the ocean is a primary need for reforming models. Winds are among the drivers of convection, thus an accurate representation of winds is essential for better convective parameterizations. We focus on the temporal variability and vertical distribution of lower-tropospheric wind biases in operational medium-range weather forecasts and ERA5 reanalyses produced with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Thanks to several sensitivity experiments and an unprecedented wealth of measurements from the 2020 EUREC4A field campaign, we show that the wind bias varies greatly from day to day, resulting in RSME's up to 2.5 m s−1, with a mean wind speed bias up to −1 m s−1 near and above the trade-inversion in the forecasts and up to −0.5 m s−1 in reanalyses. The modeled zonal and meridional wind exhibit a too strong diurnal cycle, leading to a weak wind speed bias everywhere up to 5 km during daytime, turning into a too strong wind speed bias below 2 km at nighttime. The biases are fairly insensitive to the assimilation of sondes and likely related to remote convection and large scale pressure gradients. Convective momentum transport acts to distribute biases throughout the lowest 1.5 km, whereas at higher levels, other unresolved or dynamical tendencies play a role in setting the bias. Below 1 km, modelled friction due to unresolved physical processes appears too strong, but is (partially) compensated by dynamical tendencies, making this a challenging coupled problem.

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