Forecast skill of the Indian monsoon and its onset in the ECMWF seasonal forecasting system 5 (SEAS5)

AbstractAccurate forecasting of variations in Indian monsoon precipitation and progression on seasonal time scales remains a challenge for prediction centres. We examine prediction skill for the seasonal-mean Indian summer monsoon and its onset in the European Centre for Medium-Range Weather Forecasts (ECMWF) seasonal forecasting system 5 (SEAS5). We analyse summer hindcasts initialised on 1st of May, with 51 ensemble members, for the 36-year period of 1981–2016. We evaluate the hindcasts against the Global Precipitation Climatology Project (GPCP) precipitation observations and the ECMWF reanalysis 5 (ERA5). The model has significant skill at forecasting dynamical features of the large-scale monsoon and local-scale monsoon onset tercile category one month in advance. SEAS5 shows higher skill for monsoon features calculated using large-scale indices compared to those at smaller scales. Our results also highlight possible model deficiencies in forecasting the all India monsoon rainfall.

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Addressing model error through atmospheric stochastic physical parametrizations: impact on the coupled ECMWF seasonal forecasting system

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2013.0290 ◽

2014 ◽

Vol 372 (2018) ◽

pp. 20130290 ◽

Cited By ~ 55

Author(s):

Antje Weisheimer ◽

Susanna Corti ◽

Tim Palmer ◽

Frederic Vitart

Keyword(s):

Time Scales ◽

Weather Prediction ◽

Seasonal Forecasting ◽

Near Surface ◽

Weather Forecasts ◽

European Centre ◽

Medium Range ◽

Forecasting System ◽

The Impact ◽

Stochastically Perturbed

The finite resolution of general circulation models of the coupled atmosphere–ocean system and the effects of sub-grid-scale variability present a major source of uncertainty in model simulations on all time scales. The European Centre for Medium-Range Weather Forecasts has been at the forefront of developing new approaches to account for these uncertainties. In particular, the stochastically perturbed physical tendency scheme and the stochastically perturbed backscatter algorithm for the atmosphere are now used routinely for global numerical weather prediction. The European Centre also performs long-range predictions of the coupled atmosphere–ocean climate system in operational forecast mode, and the latest seasonal forecasting system—System 4—has the stochastically perturbed tendency and backscatter schemes implemented in a similar way to that for the medium-range weather forecasts. Here, we present results of the impact of these schemes in System 4 by contrasting the operational performance on seasonal time scales during the retrospective forecast period 1981–2010 with comparable simulations that do not account for the representation of model uncertainty. We find that the stochastic tendency perturbation schemes helped to reduce excessively strong convective activity especially over the Maritime Continent and the tropical Western Pacific, leading to reduced biases of the outgoing longwave radiation (OLR), cloud cover, precipitation and near-surface winds. Positive impact was also found for the statistics of the Madden–Julian oscillation (MJO), showing an increase in the frequencies and amplitudes of MJO events. Further, the errors of El Niño southern oscillation forecasts become smaller, whereas increases in ensemble spread lead to a better calibrated system if the stochastic tendency is activated. The backscatter scheme has overall neutral impact. Finally, evidence for noise-activated regime transitions has been found in a cluster analysis of mid-latitude circulation regimes over the Pacific–North America region.

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Spatial and Temporal Variation of Precipitation in Greece and Surrounding Regions Based on Global Precipitation Climatology Project Data

Journal of Climate ◽

10.1175/2007jcli1682.1 ◽

2008 ◽

Vol 21 (6) ◽

pp. 1349-1370 ◽

Cited By ~ 28

Author(s):

N. Hatzianastassiou ◽

B. Katsoulis ◽

J. Pnevmatikos ◽

V. Antakis

Keyword(s):

Large Scale ◽

Precipitation Amount ◽

Global Precipitation Climatology Project ◽

Spatial And Temporal Variation ◽

Mean Annual Precipitation ◽

Study Region ◽

Precipitation Climatology ◽

Spatial Coverage ◽

Precipitation Decrease ◽

Global Precipitation

Abstract In this study, the spatial and temporal distribution of precipitation in the broader Greek area is investigated for the 26-yr period 1979–2004 by using monthly mean satellite-based data, with complete spatial coverage, taken from the Global Precipitation Climatology Project (GPCP). The results show that there exists a clear contrast between the more rainy western Greek area (rainside) and the drier eastern one (rainshadow), whereas there is little precipitation over the islands, particularly in the southern parts. The computed long-term areal mean annual precipitation amount averaged for the study area is equal to P = 639.8 ± 44.8 mm yr−1, showing a decreasing trend of −2.32 mm yr−1 or −60.3 mm over the 26-yr study period, which corresponds to −9.4%. This decrease of precipitation, arising primarily in winter and secondarily in spring, is the result of a decreasing trend from 1979 through the 1980s, against an increase during the 1990s through the early 2000s, followed again by a decrease up to the year 2004. The performed analysis reveals an increasing trend of precipitation in the central and northern parts of the study region, contrary to an identified decreasing trend in the southern parts, which is indicative of threatening desertification processes in those areas in the context of climatic changes in the climatically sensitive Mediterranean basin. In addition, the analysis shows that the precipitation decrease is due to a corresponding decrease of maximum precipitation against rather unchanged minimum precipitation amounts. The analysis indicates that the changing precipitation patterns in the region during winter are significantly anticorrelated with the North Atlantic Oscillation (NAO) index values, against a positive correlation during summer, highlighting thus the role of large-scale circulation patterns for regional climates. The GPCP precipitation data are satisfactorily correlated with instrumental measurements from 36 stations uniformly distributed over the study area (correlation coefficient R = 0.74 for all stations; R = 0.63–0.91 for individual stations).

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Simulation of Monsoon trough and low pressure systems in CMIP6 models

10.5194/egusphere-egu2020-4049 ◽

2020 ◽

Author(s):

Praveen Veluthedathekuzhiyil ◽

Ajayamohan Ravindran ◽

Sabeerali Cherumadanakadan Thelliyil

Keyword(s):

Climate Models ◽

Monsoon Rainfall ◽

Indian Monsoon ◽

Low Pressure ◽

Monsoon Trough ◽

Warming Scenario ◽

Wide Range ◽

Future Warming ◽

Dynamical Features ◽

Low Pressure Systems

<p>Monsoon low pressure systems (LPS) contributes to more than half of the Indian monsoon rainfall. However most climate models fail to capture the characteristics of low pressure systems realistically. This aspect is scrutinized in a wide range of available CMIP6 model simulations using an objective LPS tracking algorithm. Broader features such as monsoon trough over which these systems forms are also analyzed. It has been found that, majority of the models fail to realistically represent these two important features. However few models that were able to capture these events in CMIP5 are able to simulate them in CMIP6 as well. We examine the dynamical features that lead to realistic simulation of LPS in these set of models. Selected good models are then used to study the characteristics of LPS in a future warming scenario. This study will help in judging the performance of models and for any future improvements.</p>

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

Monthly Weather Review ◽

10.1175/2008mwr2390.1 ◽

2008 ◽

Vol 136 (11) ◽

pp. 4301-4319 ◽

Cited By ~ 22

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.

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

Monthly Weather Review ◽

10.1175/mwr-d-12-00164.1 ◽

2013 ◽

Vol 141 (6) ◽

pp. 1943-1962 ◽

Cited By ~ 13

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.

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Impact of Coupling with an Ice–Ocean Model on Global Medium-Range NWP Forecast Skill

Monthly Weather Review ◽

10.1175/mwr-d-17-0157.1 ◽

2018 ◽

Vol 146 (4) ◽

pp. 1157-1180 ◽

Cited By ~ 19

Author(s):

Gregory C. Smith ◽

Jean-Marc Bélanger ◽

François Roy ◽

Pierre Pellerin ◽

Hal Ritchie ◽

...

Keyword(s):

Standard Deviation ◽

Large Scale ◽

Weather Forecasting ◽

Positive Impact ◽

Weather Prediction ◽

Ocean Model ◽

Forecast Skill ◽

Medium Range ◽

Forecasting System ◽

The Impact

The importance of coupling between the atmosphere and the ocean for forecasting on time scales of hours to weeks has been demonstrated for a range of physical processes. Here, the authors evaluate the impact of an interactive air–sea coupling between an operational global deterministic medium-range weather forecasting system and an ice–ocean forecasting system. This system was developed in the context of an experimental forecasting system that is now running operationally at the Canadian Centre for Meteorological and Environmental Prediction. The authors show that the most significant impact is found to be associated with a decreased cyclone intensification, with a reduction in the tropical cyclone false alarm ratio. This results in a 15% decrease in standard deviation errors in geopotential height fields for 120-h forecasts in areas of active cyclone development, with commensurate benefits for wind, temperature, and humidity fields. Whereas impacts on surface fields are found locally in the vicinity of cyclone activity, large-scale improvements in the mid-to-upper troposphere are found with positive global implications for forecast skill. Moreover, coupling is found to produce fairly constant reductions in standard deviation error growth for forecast days 1–7 of about 5% over the northern extratropics in July and August and 15% over the tropics in January and February. To the authors’ knowledge, this is the first time a statistically significant positive impact of coupling has been shown in an operational global medium-range deterministic numerical weather prediction framework.

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An assessment of the accuracy of the RTTOV fast radiative transfer model using IASI data

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-9491-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 9491-9535 ◽

Cited By ~ 8

Author(s):

M. Matricardi

Keyword(s):

Radiative Transfer ◽

Regression Coefficients ◽

Radiative Transfer Model ◽

Transfer Model ◽

Weather Forecasts ◽

Medium Range ◽

Forecasting System ◽

Relative Differences ◽

Temperature Water

Abstract. IASI measurements of spectral radiances made between the 1 April 2008 and the 15 April 2008 are compared with simulations performed using the RTTOV fast radiative transfer model utilizing regression coefficients based on different line-by-line models. The comparisons are performed within the framework of the European Centre for Medium-Range Weather Forecasts Integrated Forecasting System using fields of temperature, water vapour and ozone obtained from short-range forecasts. Simulations are performed to assess the accuracy of the RTTOV computations and investigate relative differences between the line-by-line models and the quality of the spectroscopic databases on which the RTTOV coefficients are based.

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Sensitivity, Structure, and Dynamics of Singular Vectors Associated with Hurricane Helene (2006)

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-048.1 ◽

2012 ◽

Vol 69 (2) ◽

pp. 675-694 ◽

Cited By ~ 15

Author(s):

Simon T. K. Lang ◽

Sarah C. Jones ◽

Martin Leutbecher ◽

Melinda S. Peng ◽

Carolyn A. Reynolds

Keyword(s):

Three Dimensional ◽

Growth Dynamics ◽

Ensemble Forecasts ◽

Weather Forecasts ◽

Singular Vectors ◽

Medium Range ◽

Flow Features ◽

Forecasting System ◽

Diabatic Processes ◽

The Impact

Abstract The sensitivity of singular vectors (SVs) associated with Hurricane Helene (2006) to resolution and diabatic processes is investigated. Furthermore, the dynamics of their growth are analyzed. The SVs are calculated using the tangent linear and adjoint model of the integrated forecasting system (IFS) of the European Centre for Medium-Range Weather Forecasts with a spatial resolution up to TL255 (~80 km) and 48-h optimization time. The TL255 moist (diabatic) SVs possess a three-dimensional spiral structure with significant horizontal and vertical upshear tilt within the tropical cyclone (TC). Also, their amplitude is larger than that of dry and lower-resolution SVs closer to the center of Helene. Both higher resolution and diabatic processes result in stronger growth being associated with the TC compared to other flow features. The growth of the SVs in the vicinity of Helene is associated with baroclinic and barotropic mechanisms. The combined effect of higher resolution and diabatic processes leads to significant differences of the SV structure and growth dynamics within the core and in the vicinity of the TC. If used to initialize ensemble forecasts with the IFS, the higher-resolution moist SVs cause larger spread of the wind speed, track, and intensity of Helene than their lower-resolution or dry counterparts. They affect the outflow of the TC more strongly, resulting in a larger downstream impact during recurvature. Increasing the resolution or including diabatic effects degrades the linearity of the SVs. While the impact of diabatic effects on the linearity is small at low resolution, it becomes large at high resolution.

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Insights from a joint analysis of Indian and Chinese monsoon rainfall data

Hydrology and Earth System Sciences ◽

10.5194/hess-15-2709-2011 ◽

2011 ◽

Vol 15 (8) ◽

pp. 2709-2715 ◽

Cited By ~ 7

Author(s):

M. Zhou ◽

F. Tian ◽

U. Lall ◽

H. Hu

Keyword(s):

Large Scale ◽

Monsoon Rainfall ◽

Indian Monsoon ◽

Southern China ◽

Principal Component ◽

Northern China ◽

Rainfall Data ◽

Joint Analysis ◽

Climate Indices ◽

The Common

Abstract. Monsoon rainfall is of great importance for agricultural production in both China and India. Understanding the features of the Indian and Chinese monsoon rainfall and its long term predictability is a challenge for research. In this paper Principal Component Analysis (PCA) method was adopted to analyze Indian monsoon and Chinese monsoon separately as well as jointly during the period 1951 to 2003. The common structure of Indian monsoon and Chinese monsoon rainfall data was explored, and its correlation with large scale climate indices and thus the possibility of prediction were analyzed. The joint PCA results gives a clearer correlation map between Chinese monsoon rainfall and Indian monsoon rainfall. The common rainfall structure presents a significant teleconnection to Sea Surface Temperature anomaly (SSTa), moisture transport and other climate indices. Specifically, our result shows that Northern China would garner less rainfall when whole Indian rainfall is below normal, and with cold SSTa over the Indonesia region more rainfall would be distributed over India and Southern China. The result also shows that SSTa in the previous winter months could be a good indicator for the summer monsoon rainfall in China.

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

10.5194/acp-2018-275 ◽

2018 ◽

Cited By ~ 1

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.

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