scholarly journals The Impacts of Horizontal Grid Spacing and Cumulus Parameterization on Subseasonal Prediction in a Global Convection-Permitting Model

2020 ◽  
Vol 148 (12) ◽  
pp. 4747-4765
Author(s):  
Nicholas J. Weber ◽  
Clifford F. Mass ◽  
Daehyun Kim
Keyword(s):  
Global Model ◽  
Forecast Skill ◽  
Cumulus Parameterization ◽  
Madden Julian Oscillation ◽  
Grid Spacing ◽  
Variable Resolution ◽  
Channel Simulation ◽  
Convective Parameterization ◽  
Tropical Precipitation ◽  
The Tropics

AbstractMonthlong simulations targeting four Madden–Julian oscillation events made with several global model configurations are verified against observations to assess the roles of grid spacing and convective parameterization on the representation of tropical convection and midlatitude forecast skill. Specifically, the performance of a global convection-permitting model (CPM) configuration with a uniform 3-km mesh is compared to that of a global 15-km mesh with and without convective parameterization, and of a variable-resolution “channel” simulation using 3-km grid spacing only in the tropics with a scale-aware convection scheme. It is shown that global 3-km simulations produce realistic tropical precipitation statistics, except for an overall wet bias and delayed diurnal cycle. The channel simulation performs similarly, although with an unrealistically higher frequency of heavy rain. The 15-km simulations with and without cumulus schemes produce too much light and heavy tropical precipitation, respectively. Without convection parameterization, the 15-km global model produces unrealistically abundant, short-lived, and intense convection throughout the tropics. Only the global CPM configuration is able to capture eastward-propagating Madden–Julian oscillation events, and the 15-km runs favor stationary or westward-propagating convection organized at the planetary scale. The global 3-km CPM exhibits the highest extratropical forecast skill aloft and at the surface, particularly during week 3 of each hindcast. Although more cases are needed to confirm these results, this study highlights many potential benefits of using global CPMs for subseasonal forecasting. Furthermore, results show that alternatives to global convection-permitting resolution—using coarser or spatially variable resolution—feature compromises that may reduce their predictive performance.

scholarly journals Sensitivities of the Madden–Julian oscillation forecasts to configurations of physics in the ECMWF global model

2021 ◽  
Vol 21 (6) ◽  
pp. 4759-4778
Author(s):  
Jun-Ichi Yano ◽  
Nils P. Wedi
Keyword(s):  
Forecast Model ◽  
Global Model ◽  
Madden Julian Oscillation ◽  
Forecast Performance ◽  
Theoretical Investigations ◽  
Forecast Models ◽  
Forecasting System ◽  
The Rich ◽  
The Tropics ◽  
Original Motivation

Abstract. The sensitivities of the Madden–Julian oscillation (MJO) forecasts to various different configurations of the parameterized physics are examined with the global model of ECMWF's Integrated Forecasting System (IFS). The motivation for the study was to simulate the MJO as a nonlinear free wave under active interactions with higher-latitude Rossby waves. To emulate free dynamics in the IFS, various momentum-dissipation terms (“friction”) as well as diabatic heating were selectively turned off over the tropics for the range of the latitudes from 20∘ S to 20∘ N. The reduction of friction sometimes improves the MJO forecasts, although without any systematic tendency. Contrary to the original motivation, emulating free dynamics with an operational forecast model turned out to be rather difficult, because forecast performance sensitively depends on the specific type of friction turned off. The result suggests the need for theoretical investigations that much more closely follow the actual formulations of model physics: a naive approach with a dichotomy of with or without friction simply fails to elucidate the rich behaviour of complex operational models. The paper further exposes the importance of physical processes other than convection for simulating the MJO in global forecast models.

scholarly journals Detecting and Tracking Coastal Precipitation in the Tropics: Methods and Insights into Multiscale Variability of Tropical Precipitation

2020 ◽  
Vol 33 (15) ◽  
pp. 6689-6705
Author(s):  
David Coppin ◽  
Gilles Bellon ◽  
Alexander Pletzer ◽  
Chris Scott
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
Total Rainfall ◽  
Tropical Precipitation ◽  
Precipitation Estimates ◽  
Summer Hemisphere ◽  
The Tropics ◽  
Climate Prediction Center

AbstractWe propose an algorithm to detect and track coastal precipitation systems and we apply it to 18 years of the high-resolution (8 km and 30 min) Climate Prediction Center CMORPH precipitation estimates in the tropics. Coastal precipitation in the Maritime Continent and Central America contributes to up to 80% of the total rainfall. It also contributes strongly to the diurnal cycle over land with the largest contribution from systems lasting between 6 and 12 h and contributions from longer-lived systems peaking later in the day. While the diurnal cycle of coastal precipitation is more intense over land in the summer hemisphere, its timing is independent of seasons over both land and ocean because the relative contributions from systems of different lifespans are insensitive to the seasonal cycle. We investigate the hypothesis that coastal precipitation is enhanced prior to the arrival of the Madden–Julian oscillation (MJO) envelope over the Maritime Continent. Our results support this hypothesis and show that, when considering only coastal precipitation, the diurnal cycle appears reinforced even earlier over islands than previously reported. We discuss the respective roles of coastal and large-scale precipitation in the propagation of the MJO over the Maritime Continent. We also document a shift in diurnal cycle with the phases of the MJO, which results from changes in the relative contributions of short-lived versus long-lived coastal systems.

scholarly journals Subseasonal Weather Prediction in a Global Convection-Permitting Model

2019 ◽  
Vol 100 (6) ◽  
pp. 1079-1089 ◽  
Author(s):  
Nicholas J. Weber ◽  
Clifford F. Mass
Keyword(s):  
Time Scales ◽  
Numerical Models ◽  
Weather Prediction ◽  
Small Sample ◽  
Tropical Convection ◽  
Grid Spacing ◽  
Tropical Precipitation ◽  
Predictive Skill ◽  
The Tropics ◽  
Horizontal Grid

AbstractAlthough accurate weather and climate prediction beyond one to two weeks is of great value to society, the skill of such extended prediction is limited in current operational global numerical models, whose coarse horizontal grid spacing necessitates the parameterization of atmospheric processes. Of particular concern is the parameterization of convection and specifically convection in the tropics, which impacts global weather at all time scales through atmospheric teleconnections. Convection-permitting models, which forego convective parameterization by explicitly resolving cumulus-scale motions using fine (1–4 km) horizontal grid spacing, can improve global prediction at extended time scales by more faithfully simulating tropical convection and associated teleconnections. This study demonstrates that convection-permitting resolution in a global numerical model can improve both the statistical features of tropical precipitation and extended predictive skill in the tropics and midlatitudes. Comparing four monthlong global simulations with 3-km grid spacing to coarser-resolution simulations that parameterize convection reveals that convection-permitting simulations improve tropical precipitation rates and the diurnal cycle of tropical convection. The propagation of the Madden–Julian oscillation was better predicted in three of the four 3-km simulations; these three runs also featured more skillful prediction of weekly extratropical circulation anomalies, particularly during week 3 of each forecast. These results, though based on a small sample of four cases, demonstrate that convection-permitting global modeling can benefit extended atmospheric prediction and offers the potential for improved operational subseasonal forecast skill.

scholarly journals Dipole patterns in tropical precipitation were pervasive across landmasses throughout Marine Isotope Stage 5

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Katrina Nilsson-Kerr ◽  
Pallavi Anand ◽  
Philip B. Holden ◽  
Steven C. Clemens ◽  
Melanie J. Leng
Keyword(s):  
Large Scale ◽  
Marine Isotope Stage ◽  
Convergence Zone ◽  
Inter Tropical Convergence Zone ◽  
Tropical Regions ◽  
Tropical Precipitation ◽  
Rainfall Patterns ◽  
Marine Isotope Stage 5 ◽  
Climate Cooling ◽  
The Tropics

AbstractMost of Earth’s rain falls in the tropics, often in highly seasonal monsoon rains, which are thought to be coupled to the inter-hemispheric migrations of the Inter-Tropical Convergence Zone in response to the seasonal cycle of insolation. Yet characterization of tropical rainfall behaviour in the geologic past is poor. Here we combine new and existing hydroclimate records from six large-scale tropical regions with fully independent model-based rainfall reconstructions across the last interval of sustained warmth and ensuing climate cooling between 130 to 70 thousand years ago (Marine Isotope Stage 5). Our data-model approach reveals large-scale heterogeneous rainfall patterns in response to changes in climate. We note pervasive dipole-like tropical precipitation patterns, as well as different loci of precipitation throughout Marine Isotope Stage 5 than recorded in the Holocene. These rainfall patterns cannot be solely attributed to meridional shifts in the Inter-Tropical Convergence Zone.

scholarly journals Corrections for Temporal Discontinuities in the OPI

2010 ◽  
Vol 27 (3) ◽  
pp. 457-469 ◽  
Author(s):  
M. R. P. Sapiano ◽  
J. E. Janowiak ◽  
P. A. Arkin ◽  
H. Lee ◽  
T. M. Smith ◽  
...  
Keyword(s):  
High Resolution ◽  
Longwave Radiation ◽  
Infrared Observations ◽  
Tropical Precipitation ◽  
Corrected Version ◽  
Crossing Time ◽  
Orbital Drift ◽  
Mean Square Difference ◽  
The Tropics ◽  
Orbiting Spacecraft

Abstract The longest record of precipitation estimated from satellites is the outgoing longwave radiation (OLR) precipitation index (OPI), which is based on polar-orbiting infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) instrument that has flown onboard successive NOAA satellites. A significant barrier to the use of these data in studies of the climate of tropical precipitation (among other things) is the large bias caused by orbital drift that is present in the OLR data. Because the AVHRR instruments are deployed on the polar-orbiting spacecraft, OLR observations are recorded at specific times for each earth location for each day. Discontinuities are caused by the use of multiple satellites with different observing times as well as the orbital drift that occurs throughout the lifetime of each satellite. A regression-based correction is proposed based solely on the equator crossing time (ECT). The correction allows for separate means for each satellite as well as separate coefficients for each satellite ECT. The correction is calculated separately for each grid box but is applied only at locations where the correction is correlated with the OLR estimate. Thus, the correction is applied only where deemed necessary. The OPI is used to estimate precipitation from the OLR estimates based on the new corrected version of the OLR, the uncorrected OLR, and two earlier published corrected versions. One of the earlier corrections is derived by removing variations from AVHRR based on EOFs that are identified as containing spurious variations related to the ECT bias, whereas the other is based on OLR estimates from the High Resolution Infrared Radiation Sounder (HIRS) that have been corrected using diurnal models for each grid box. The new corrected version is shown to be free of nearly all of the ECT bias and has the lowest root mean square difference when compared to gauges and passive microwave estimates of precipitation. The EOF-based correction fails to remove all of the variations related to the ECT bias, whereas the correction based on HIRS removes much of the bias but appears to introduce erroneous trends caused by the water vapor signal to which these data are sensitive. The new correction for AVHRR OLR works well in the tropics where the OPI has the most skill, but users should be careful when interpreting trends outside this region.

scholarly journals Tropical and Midlatitude Impact on Seasonal Polar Predictability in the Community Earth System Model

2019 ◽  
Vol 32 (18) ◽  
pp. 5997-6014 ◽  
Author(s):  
Edward Blanchard-Wrigglesworth ◽  
Qinghua Ding
Keyword(s):  
Forecast Skill ◽  
Specific Humidity ◽  
The Arctic ◽  
The North ◽  
Perfect Model ◽  
Community Earth System Model ◽  
Free Running ◽  
Skill Improvement ◽  
The Tropics ◽  
The Impact

Abstract The impact on seasonal polar predictability from improved tropical and midlatitude forecasts is explored using a perfect-model experiment and applying a nudging approach in a GCM. We run three sets of 7-month long forecasts: a standard free-running forecast and two nudged forecasts in which atmospheric winds, temperature, and specific humidity (U, V, T, Q) are nudged toward one of the forecast runs from the free ensemble. The two nudged forecasts apply the nudging over different domains: the tropics (30°S–30°N) and the tropics and midlatitudes (55°S–55°N). We find that the tropics have modest impact on forecast skill in the Arctic or Antarctica both for sea ice and the atmosphere that is mainly confined to the North Pacific and Bellingshausen–Amundsen–Ross Seas, whereas the midlatitudes greatly improve Arctic winter and Antarctic year-round forecast skill. Arctic summer forecast skill from May initialization is not strongly improved in the nudged forecasts relative to the free forecast and is thus mostly a “local” problem. In the atmosphere, forecast skill improvement from midlatitude nudging tends to be largest in the polar stratospheres and decreases toward the surface.

scholarly journals Improved forecast skill in the tropics in the new MiKlip decadal climate predictions

2013 ◽  
Vol 40 (21) ◽  
pp. 5798-5802 ◽  
Author(s):  
H. Pohlmann ◽  
W. A. Müller ◽  
K. Kulkarni ◽  
M. Kameswarrao ◽  
D. Matei ◽  
...  
Keyword(s):  
Forecast Skill ◽  
Decadal Climate ◽  
The Tropics

scholarly journals Verification of precipitation forecasts of MM5 model over Epirus, NW Greece, for various convective parameterization schemes

2012 ◽  
Vol 12 (5) ◽  
pp. 1393-1405 ◽  
Author(s):  
O. A. Sindosi ◽  
A. Bartzokas ◽  
V. Kotroni ◽  
K. Lagouvardos
Keyword(s):  
Horizontal Resolution ◽  
Forecast Skill ◽  
Precipitation Forecast ◽  
Meteorological Model ◽  
Convective Parameterization ◽  
Parameterization Schemes ◽  
Mm5 Model ◽  
Convective Parameterization Scheme ◽  
High Precipitation Events ◽  
High Precipitation

Abstract. The mesoscale meteorological model MM5 is applied to 22 selected days with intense precipitation in the region of Epirus, NW Greece. At first, it was investigated whether and to what extend an increased horizontal resolution (from 8 to 2 km) improves the quantitative precipitation forecasts. The model skill was examined for the 12-h accumulated precipitation recorded at 14 meteorological stations located in Epirus and by using categorical and descriptive statistics. Then, the precipitation forecast skill for the 2 km grid was studied: (a) without and (b) with the activation of a convective parameterization scheme. From the above study, the necessity of the use of a scheme at the 2 km grid is assessed. Furthermore, three different convective parameterization schemes are compared: (a) Betts-Miller, (b) Grell and (c) Kain-Fritsch-2 in order to reveal the scheme, resulting in the best precipitation forecast skill in Epirus. Kain-Fritsch-2 and Grell give better results with the latter being the best for the high precipitation events.

scholarly journals The Madden–Julian Oscillation and Boreal Winter Forecast Skill: An Analysis of NCEP CFSv2 Reforecasts

2015 ◽  
Vol 28 (15) ◽  
pp. 6297-6307 ◽  
Author(s):  
Charles Jones ◽  
Abheera Hazra ◽  
Leila M. V. Carvalho
Keyword(s):  
Forecast Skill ◽  
Western Pacific ◽  
Boreal Winter ◽  
Lead Times ◽  
Madden Julian Oscillation ◽  
Main Mode ◽  
Weather Forecasts ◽  
Synoptic Variability ◽  
The Impact ◽  
The Western Pacific

Abstract The Madden–Julian oscillation (MJO) is the main mode of tropical intraseasonal variations and bridges weather and climate. Because the MJO has a slow eastward propagation and longer time scale relative to synoptic variability, significant interest exists in exploring the predictability of the MJO and its influence on extended-range weather forecasts (i.e., 2–4-week lead times). This study investigates the impact of the MJO on the forecast skill in Northern Hemisphere extratropics during boreal winter. Several 45-day forecasts of geopotential height (500 hPa) from NCEP Climate Forecast System version 2 (CFSv2) reforecasts are used (1 November–31 March 1999–2010). The variability of the MJO expressed as different amplitudes, durations, and recurrence (i.e., primary and successive events) and their influence on forecast skill is analyzed and compared against inactive periods (i.e., null cases). In general, forecast skill during enhanced MJO convection over the western Pacific is systematically higher than in inactive days. When the enhanced MJO convection is over the Maritime Continent, forecasts are lower than in null cases, suggesting potential model deficiencies in accurately forecasting the eastward propagation of the MJO over that region and the associated extratropical response. In contrast, forecasts are more skillful than null cases when the enhanced convection is over the western Pacific and during long, intense, and successive MJO events. These results underscore the importance of the MJO as a potential source of predictability on 2–4-week lead times.

scholarly journals The Madden‐Julian Oscillation Affects Maize Yields Throughout the Tropics and Subtropics

2020 ◽  
Vol 47 (11) ◽  
Author(s):  
W. B. Anderson ◽  
E. Han ◽  
W. Baethgen ◽  
L. Goddard ◽  
Á. G. Muñoz ◽  
...  
Keyword(s):  
Madden Julian Oscillation ◽  
Maize Yields ◽  
The Tropics
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