MesoLAPS Predictions of Low-Level Convergence Lines over Northeastern Australia

Abstract The prediction of low-level convergence lines over northeastern Australia such as those which give rise to the “morning glory” phenomenon and the north Australian cloud line (NACL) are investigated using MesoLAPS, a mesoscale version of the Australian Bureau of Meteorology’s operational Limited Area Prediction System. The model is used also to examine aspects of the dynamics of such lines. The predictions were made during the Gulf Lines Experiment in 2002 and are compared here with data collected during the experiment. The ability of MesoLAPS to forecast the convergence lines is investigated in detail for selected cases. In two cases with well-developed southerly morning glory disturbances, the model was able to capture the separation of a borelike disturbance from an airmass change, although the model does not have the resolution to capture the wavelike structures that develop at the leading edge of the bore waves. An analysis of the entire 44-day period between 11 September and 24 October shows that MesoLAPS has significant skill in forecasting the lines, but it does not capture all of them. About 85% of forecasts of northeasterly morning glories and southerly morning glories, or of their nonoccurrence, were correct, while the corresponding percentage for the NACL was about 65%. However, about 15% of northeasterly morning glories and about 35% of NACL events that occurred were not forecast by the model. Also, only 6 out of 11 southerly morning glories were forecast. A detailed analysis of the MesoLAPS calculations indicates that the broad-scale generation mechanisms of northeasterly and southerly morning glories are similar and it enables the construction of a conceptual model for the generation of southerly morning glories.

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Analysis of the 13–14 July Gulf Surge Event during the 2004 North American Monsoon Experiment

Monthly Weather Review ◽

10.1175/mwr3450.1 ◽

2007 ◽

Vol 135 (9) ◽

pp. 3098-3117 ◽

Cited By ~ 24

Author(s):

Peter J. Rogers ◽

Richard H. Johnson

Keyword(s):

North American ◽

Gulf Of California ◽

Leading Edge ◽

North American Monsoon ◽

Strong Wind ◽

Kelvin Wave ◽

High Resolution Data ◽

Low Level ◽

Second Stage ◽

The North

Abstract Gulf surges are disturbances that move northward along the Gulf of California (GOC), frequently advecting cool, moist air from the GOC or eastern tropical Pacific Ocean into the deserts of the southwest United States and northwest Mexico during the North American Monsoon (NAM). Little attention has been given to the dynamics of these disturbances because of the lack of reliable high-resolution data across the NAM region. High temporal and spatial observations collected during the 2004 North American Monsoon Experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13–14 July 2004. Integrated Sounding Systems deployed along the east coast of the GOC and an enhanced network of rawinsonde sites across the NAM region are used in this study. Observations show that the 13–14 July gulf surge occurred in two primary stages. The first stage was preceded by anomalous low-level warming along the northern GOC on 13 July. Sharp cooling, moistening, and increased low-level south-southeasterly flow followed over a 12–18-h period. Over the northern gulf, the wind reached ∼20 m s−1 at 750 m AGL. Then there was a brief respite followed by the second stage—a similar, but deeper acceleration of the southerly flow associated with the passage of Tropical Storm (TS) Blas on 14 July. The initial surge disturbance traversed the GOC at a speed of ∼17–25 m s−1 and resulted in a deepening of the mixed layer along the northern gulf. Dramatic surface pressure rises also accompanied the surge. The weight of the evidence suggests that the first stage of the overall surge itself consisted of two parts. The initial part resembled borelike disturbances initiated by convective downdrafts impinging on the low-level stable layer over the region. The secondary part was characteristic of a Kelvin wave–type disturbance, as evident in the deeper layer of sharp cooling and strong wind that ensued. Another possible explanation for the first part is that the leading edge of this Kelvin wave steepened nonlinearly into a borelike disturbance. The second stage of the surge was associated with the increased circulation around TS Blas.

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Storm-Scale Data Assimilation and Ensemble Forecasting with the NSSL Experimental Warn-on-Forecast System. Part I: Radar Data Experiments

Weather and Forecasting ◽

10.1175/waf-d-15-0043.1 ◽

2015 ◽

Vol 30 (6) ◽

pp. 1795-1817 ◽

Cited By ~ 61

Author(s):

Dustan M. Wheatley ◽

Kent H. Knopfmeier ◽

Thomas A. Jones ◽

Gerald J. Creager

Keyword(s):

Data Assimilation ◽

Leading Edge ◽

Radar Data ◽

Ensemble Forecasts ◽

Low Level ◽

The North ◽

Weather Events ◽

Probabilistic Forecasts ◽

Bow Echo ◽

System Part

Abstract This first part of a two-part study on storm-scale radar and satellite data assimilation provides an overview of a multicase study conducted as part of the NOAA Warn-on-Forecast (WoF) project. The NSSL Experimental WoF System for ensembles (NEWS-e) is used to produce storm-scale analyses and forecasts of six diverse severe weather events from spring 2013 and 2014. In this study, only Doppler reflectivity and radial velocity observations (and, when available, surface mesonet data) are assimilated into a 36-member, storm-scale ensemble using an ensemble Kalman filter (EnKF) approach. A series of 1-h ensemble forecasts are then initialized from storm-scale analyses during the 1-h period preceding the onset of storm reports. Of particular interest is the ability of these 0–1-h ensemble forecasts to reproduce the low-level rotational characteristics of supercell thunderstorms, as well as other convective hazards. For the tornado-producing thunderstorms considered in this study, ensemble probabilistic forecasts of low-level rotation generally indicated a rotating thunderstorm approximately 30 min before the time of first observed tornado. Displacement errors (often to the north of tornado-affected areas) associated with vorticity swaths were greatest in those forecasts launched 30–60 min before the time of first tornado. Similar forecasts were produced for a tornadic mesovortex along the leading edge of a bow echo and, again, highlighted a well-defined vorticity swath as much as 30 min prior to the first tornado.

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Aircraft Observations of the 12–15 July 2004 Moisture Surge Event during the North American Monsoon Experiment

Monthly Weather Review ◽

10.1175/2010mwr3228.1 ◽

2010 ◽

Vol 138 (9) ◽

pp. 3498-3513 ◽

Cited By ~ 7

Author(s):

John F. Mejia ◽

Michael W. Douglas ◽

Peter J. Lamb

Keyword(s):

North American ◽

Gulf Of California ◽

Leading Edge ◽

Moisture Flux ◽

North American Monsoon ◽

Low Level ◽

The North ◽

Order Of Magnitude ◽

Anomaly Analysis ◽

Moist Layer

Abstract This paper describes aspects of a strong moisture surge over the Gulf of California that was observed during the 2004 North American Monsoon Experiment. Although a variety of special observation platforms aid the analyses, the authors focus on observations collected during two NOAA research aircraft flights made on 12 and 13 July. These flights sampled the initial and mature phases of a strong surge associated with Tropical Storm Blas. The first flight is identified by both a convective outflow and another feature, both deeper and with larger spatial scale, ahead of the outflow in association with the surge’s leading edge. The surge speed, ~18 m s−1, was identified from anomaly analysis of surface station pressure data. Observations show interesting multiscale features associated with the surge during its initial stages but do not allow for unambiguous identification of the surge’s forcing mechanism or dynamical properties. Data from the second flight were used to describe the along- and cross-gulf structure of the enhanced low-level flow associated with the surge event. The strongest winds were over the northernmost gulf, with weaker winds over the surrounding coastal areas. The kinematic moisture flux increased toward the northern gulf; wind speed is the main control on the flux as the moist layer shows only small horizontal gradients. Over the northern gulf, the combination of a very shallow moist layer and a shallow low-level jet yield maximum moisture fluxes near 950 hPa that are almost an order of magnitude larger than those at 850 hPa.

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Dynamical Downscaling of ERA5 Data on the North-Western Mediterranean Sea: From Atmosphere to High-Resolution Coastal Wave Climate

Journal of Marine Science and Engineering ◽

10.3390/jmse9020208 ◽

2021 ◽

Vol 9 (2) ◽

pp. 208

Author(s):

Valentina Vannucchi ◽

Stefano Taddei ◽

Valerio Capecchi ◽

Michele Bendoni ◽

Carlo Brandini

Keyword(s):

Mediterranean Sea ◽

Wind Wave ◽

Dynamical Downscaling ◽

Wave Climate ◽

Western Mediterranean ◽

Limited Area ◽

Computational Domain ◽

Wave Hindcast ◽

The North ◽

Western Mediterranean Sea

A 29-year wind/wave hindcast is produced over the Mediterranean Sea for the period 1990–2018. The dataset is obtained by downscaling the ERA5 global atmospheric reanalyses, which provide the initial and boundary conditions for a numerical chain based on limited-area weather and wave models: the BOLAM, MOLOCH and WaveWatch III (WW3) models. In the WW3 computational domain, an unstructured mesh is used. The variable resolutions reach up to 500 m along the coasts of the Ligurian and Tyrrhenian seas (Italy), the main objects of the study. The wind/wave hindcast is validated using observations from coastal weather stations and buoys. The wind validation provides velocity correlations between 0.45 and 0.76, while significant wave height correlations are much higher—between 0.89 and 0.96. The results are also compared to the original low-resolution ERA5 dataset, based on assimilated models. The comparison shows that the downscaling improves the hindcast reliability, particularly in the coastal regions, and especially with regard to wind and wave directions.

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Extended Prediction of North Indian Ocean Tropical Cyclones

Weather and Forecasting ◽

10.1175/waf-d-11-00083.1 ◽

2012 ◽

Vol 27 (3) ◽

pp. 757-769 ◽

Cited By ~ 31

Author(s):

James I. Belanger ◽

Peter J. Webster ◽

Judith A. Curry ◽

Mark T. Jelinek

Keyword(s):

Tropical Cyclone ◽

Indian Ocean ◽

Tropical Cyclones ◽

North Indian Ocean ◽

Ensemble Prediction ◽

Tropical Cyclone Genesis ◽

Lead Times ◽

Prediction System ◽

Ensemble Prediction System ◽

The North

Abstract This analysis examines the predictability of several key forecasting parameters using the ECMWF Variable Ensemble Prediction System (VarEPS) for tropical cyclones (TCs) in the North Indian Ocean (NIO) including tropical cyclone genesis, pregenesis and postgenesis track and intensity projections, and regional outlooks of tropical cyclone activity for the Arabian Sea and the Bay of Bengal. Based on the evaluation period from 2007 to 2010, the VarEPS TC genesis forecasts demonstrate low false-alarm rates and moderate to high probabilities of detection for lead times of 1–7 days. In addition, VarEPS pregenesis track forecasts on average perform better than VarEPS postgenesis forecasts through 120 h and feature a total track error growth of 41 n mi day−1. VarEPS provides superior postgenesis track forecasts for lead times greater than 12 h compared to other models, including the Met Office global model (UKMET), the Navy Operational Global Atmospheric Prediction System (NOGAPS), and the Global Forecasting System (GFS), and slightly lower track errors than the Joint Typhoon Warning Center. This paper concludes with a discussion of how VarEPS can provide much of this extended predictability within a probabilistic framework for the region.

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NAO predictability from external forcing in the late 20th century

npj Climate and Atmospheric Science ◽

10.1038/s41612-021-00177-8 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Jeremy M. Klavans ◽

Mark A. Cane ◽

Amy C. Clement ◽

Lisa N. Murphy

Keyword(s):

North Atlantic ◽

Radiative Forcing ◽

Climate Models ◽

North Atlantic Ocean ◽

Signal To Noise Ratio ◽

Prediction System ◽

Signal To Noise ◽

Late 20Th Century ◽

The North ◽

Predictive Skill

AbstractThe North Atlantic Oscillation (NAO) is predictable in climate models at near-decadal timescales. Predictive skill derives from ocean initialization, which can capture variability internal to the climate system, and from external radiative forcing. Herein, we show that predictive skill for the NAO in a very large uninitialized multi-model ensemble is commensurate with previously reported skill from a state-of-the-art initialized prediction system. The uninitialized ensemble and initialized prediction system produce similar levels of skill for northern European precipitation and North Atlantic SSTs. Identifying these predictable components becomes possible in a very large ensemble, confirming the erroneously low signal-to-noise ratio previously identified in both initialized and uninitialized climate models. Though the results here imply that external radiative forcing is a major source of predictive skill for the NAO, they also indicate that ocean initialization may be important for particular NAO events (the mid-1990s strong positive NAO), and, as previously suggested, in certain ocean regions such as the subpolar North Atlantic ocean. Overall, we suggest that improving climate models’ response to external radiative forcing may help resolve the known signal-to-noise error in climate models.

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Precipitation Enhancement in Squall Lines Moving Over Mountainous Coastal Regions

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0222.1 ◽

2021 ◽

Author(s):

Fan Wu ◽

Kelly Lombardo

Keyword(s):

Convective Available Potential Energy ◽

Leading Edge ◽

Sea Breeze ◽

Cold Pool ◽

Pressure Perturbation ◽

Coastal Regions ◽

Low Level ◽

Squall Lines ◽

Sloping Terrain ◽

Precipitation Enhancement

AbstractA mechanism for precipitation enhancement in squall lines moving over mountainous coastal regions is quantified through idealized numerical simulations. Storm intensity and precipitation peak over the sloping terrain as storms descend from an elevated plateau toward the coastline and encounter the marine atmospheric boundary layer (MABL). Storms are most intense as they encounter the deepest MABLs. As the descending storm outflow collides with a moving MABL (sea breeze), surface and low-level air parcels initially accelerate upward, though their ultimate trajectory is governed by the magnitude of the negative non-hydrostatic inertial pressure perturbation behind the cold pool leading edge. For shallow MABLs, the baroclinic gradient across the gust front generates large horizontal vorticity, a low-level negative pressure perturbation, and thus a downward acceleration of air parcels following their initial ascent. A deep MABL reduces the baroclinically-generated vorticity, leading to a weaker pressure perturbation and minimal downward acceleration, allowing air to accelerate into a storm’s updraft.Once storms move away from the terrain base and over the full depth of the MABLs, storms over the deepest MABLs decay most rapidly, while those over the shallowest MABLs initially intensify. Though elevated ascent exists above all MABLs, the deepest MABLs substantially reduce the depth of the high-θe layer above the MABLs and limit instability. This relationship is insensitive to MABL temperature, even though surface-based ascent is present for the less cold MABLs, the MABL thermal deficit is smaller, and convective available potential energy (CAPE) is higher.

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Broad-scale distribution of the winter protozooplankton community in the North Sea

Journal of Sea Research ◽

10.1016/j.seares.2018.11.006 ◽

2019 ◽

Vol 144 ◽

pp. 112-121

Author(s):

Franziska Bils ◽

Marta Moyano ◽

Nicole Aberle ◽

Cindy J.G. van Damme ◽

Richard D.M. Nash ◽

...

Keyword(s):

North Sea ◽

The North ◽

The North Sea ◽

Broad Scale

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A flood episode in northern Italy: multi-model and single-model mesoscale meteorological ensembles for hydrological predictions

Hydrology and Earth System Sciences ◽

10.5194/hess-17-2107-2013 ◽

2013 ◽

Vol 17 (6) ◽

pp. 2107-2120 ◽

Cited By ~ 13

Author(s):

S. Davolio ◽

M. M. Miglietta ◽

T. Diomede ◽

C. Marsigli ◽

A. Montani

Keyword(s):

Horizontal Resolution ◽

Northern Italy ◽

Ensemble Prediction ◽

Limited Area ◽

Prediction System ◽

Model Ensemble ◽

Single Model ◽

Ensemble Prediction System ◽

Forecasting System ◽

Meteorological Models

Abstract. Numerical weather prediction models can be coupled with hydrological models to generate streamflow forecasts. Several ensemble approaches have been recently developed in order to take into account the different sources of errors and provide probabilistic forecasts feeding a flood forecasting system. Within this framework, the present study aims at comparing two high-resolution limited-area meteorological ensembles, covering short and medium range, obtained via different methodologies, but implemented with similar number of members, horizontal resolution (about 7 km), and driving global ensemble prediction system. The former is a multi-model ensemble, based on three mesoscale models (BOLAM, COSMO, and WRF), while the latter, following a single-model approach, is the operational ensemble forecasting system developed within the COSMO consortium, COSMO-LEPS (limited-area ensemble prediction system). The meteorological models are coupled with a distributed rainfall-runoff model (TOPKAPI) to simulate the discharge of the Reno River (northern Italy), for a recent severe weather episode affecting northern Apennines. The evaluation of the ensemble systems is performed both from a meteorological perspective over northern Italy and in terms of discharge prediction over the Reno River basin during two periods of heavy precipitation between 29 November and 2 December 2008. For each period, ensemble performance has been compared at two different forecast ranges. It is found that, for the intercomparison undertaken in this specific study, both mesoscale model ensembles outperform the global ensemble for application at basin scale. Horizontal resolution is found to play a relevant role in modulating the precipitation distribution. Moreover, the multi-model ensemble provides a better indication concerning the occurrence, intensity and timing of the two observed discharge peaks, with respect to COSMO-LEPS. This seems to be ascribable to the different behaviour of the involved meteorological models. Finally, a different behaviour comes out at different forecast ranges. For short ranges, the impact of boundary conditions is weaker and the spread can be mainly attributed to the different characteristics of the models. At longer forecast ranges, the similar behaviour of the multi-model members forced by the same large-scale conditions indicates that the systems are governed mainly by the boundary conditions, although the different limited area models' characteristics may still have a non-negligible impact.

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