Doctor of Philosophy

dissertationForecasting tropical cyclone (TC) genesis is a challenging problem. This dissertation attempts to understand the following questions through studying the genesis of Typhoon Nuri (2008) with numerical simulations and data assimilation: 1) What are the atmospheric conditions and processes that contribute to Nuri's genesis and early rapid intensification? 2) To what extent can data assimilation improve the forecasts of Nuri's genesis? To address the first question, numerical simulations of Nuri's genesis are conducted using an advanced research version of the Weather Research and Forecasting (WRF) model. First, initial and boundary conditions derived from two global analyses are found to lead to remarkably different simulations of Nuri's genesis in developing and nondeveloping cases. It is also found that the convective development into the pre-Nuri core region is a critical process for Nuri's genesis. A strong midlevel vortex and a moist environment provide the favorable conditions for the convective development. Induced by the persistent deep convection, diabatic heating at upper levels is produced from latent heat release. This substantial warming at upper levels results in the drop in Nuri's minimum central sea level pressure. Next, the sensitivity of numerical simulations of Nuri's genesis to the model horizontal resolution is examined. Results show that the simulation at a coarse-resolution (e.g., 12 km) better predicts Nuri's rapid intensification than that at a higher resolution (e.g., 4 km). Specifically, the simulation at the coarser resolution produces strong convective bursts and diabatic heating in the inner core region and also stronger warming in the upper atmosphere, thus leading to a lower minimum sea level pressure (MSLP). Further experiments suggest that an appropriate microphysics scheme (e.g., the twomoment Morrison scheme) and a later initialization time (after Nuri's early development) could help the high-resolution simulation better capture Nuri's rapid intensification. Finally, numerical experiments are conducted to examine the impact of radar data assimilation on numerical simulations of Nuri's genesis using a four-dimensional variational data assimilation (4D-VAR) method. The radar data assimilation results in significant improvements in the numerical simulation of Nuri's genesis. Several configurations of data assimilation are evaluated. Specifically, assimilation of radial velocity leads to more improvement in intensity forecasts, whereas track forecasts are better simulated by the assimilation of radar-retrieved wind components. Improved analysis and forecasts are obtained when both radial velocity and retrieved winds are assimilated. In addition, 4D-VAR performs better than three-dimensional variational data assimilation (3D-VAR) in radar data assimilation. The positive impact of radar data assimilation can be attributed to the improved simulations of convective evolution and the enhanced midlevel vortex and moisture conditions

Using Data Assimilation To Investigate The Effect Of African Easterly Waves, Mesoscale Convective Systems, And Orography On Tropical Cyclogenesis Over Eastern Pacific

This study examines the association of tropical cyclogenesis and tropical wave activities such as African Easterly Waves (AEWs) in the Northeast Pacific Ocean. The impact of Central and Mexico Mountains on hurricane genesis, intensification and track is also studied in this paper. Eight numerical simulations using Weather Research and Forecasting (WRF-ARW) model are conducted to investigate the genesis, track and intensification of Hurricane Jimena (2009) a category 4 (on the Saffir-Simpson Hurricane Scale) hurricane during the 2009 eastern Pacific hurricane season. In addition, this study also analyzes the impact of three dimensional variational data assimilation of (3DVAR) of NCEP FNL data on WRF simulations. Based on satellite imagery and WRF analysis of Hurricane Jimena (2009), we find that the formation of Jimena on August 28, 2009 was trigged by a tropical wave from off the coast of Africa and propagated west-ward, across the Atlantic, Caribbean and into eastern Pacific on August 25. The study also reveals that initial time (or initial conditions) and microphysics scheme along with data assimilation play an important role on WRF-ARW model simulation

On the impact of initial conditions in the forecast of Hurricane Leslie extratropical transition

Hurricane Leslie (2018) was a non-tropical system that lasted for a long time undergoing several transitions between tropical and extratropical states. Its trajectory was highly uncertain and difficult to predict. Here the extratropical transition of Leslie is simulated using the Model for Prediction Across Scales (MPAS) with two different sets of initial conditions (IC): the operational analysis of the Integrate Forecast System (IFS) and the Global Forecast System (GFS).This work was partially supported by the research project PID2019-105306RB-I00/AEI/10.13039/501100011033, and the two ECMWF Special Projects (SPESMART and SPESVALE)

The UK wind regime - Observational trends and extreme event analysis and modelling

Abstract The UK has one of the most variable wind climates; NW Europe as a whole is a challenging region for forecast- and climate-modelling alike. In Europe, strong winds within extra-tropical cyclones (ETCs) remain on average the most economically significant weather peril when averaged over multiple years, so an understanding how ETCs cause extreme surface winds and how these extremes vary over time is crucial. An assessment of the 1980-2010 UK wind regime is presented based on a unique 40-station network of 10m hourly mean windspeed and daily maximum gustspeed (DMGS) surface station measurements. The regime is assessed, in the context of longer- and larger-scale wind variability, in terms of temporal trends, seasonality, spatial variation, distribution and extremes. Annual mean windspeed ranged from 4.4 to 5.4 ms-1 (a 22% difference) with 2010 recording the lowest annual network mean windspeed over the period, attracting the attention of the insurance and wind energy sectors, both highly exposed to windspeed variations. A short subjective climatology (2008-2010) is developed of the ETCs and their sub-storm features which are associated with the strongest DMGSs. The little studied UK Quasi-linear convective systems (QLCSs) and pseudo-QLCSs are found to account for 22% of the top 1% of DMGSs, with the better known Sting Jet accounting for at most 5%. This same climatology of 2008-10 ETCs then forms the basis of performance assessments of global forecast ensemble systems. At T+48, an ensemble consisting of just the ECMWF and Canadian EPS members (total-70) is found to capture the same set of extreme events as an ensemble consisting of nine global centres (157-239) highlighting the value of using model physics perturbations at this range. A prominent ETC, Emma, then forms the basis of a high-resolution model sensitivity analysis using the Weather Research and Forecasting model. Surface wind simulations display greater sensitivity to different cloud microphysics schemes and to horizontal resolution than to vertical resolution, the former highlighting the importance of diabatic processes within extreme European ETCs

Electromagnetic Radiation

The application of electromagnetic radiation in modern life is one of the most developing technologies. In this timely book, the authors comprehensively treat two integrated aspects of electromagnetic radiation, theory and application. It covers a wide scope of practical topics, including medical treatment, telecommunication systems, and radiation effects. The book sections have clear presentation, some state of the art examples, which makes this book an indispensable reference book for electromagnetic radiation applications

Role of humidity in the development and intensification of Mediterranean tropical-like cyclones (Medicanes)

In questo lavoro sono stati analizzati due casi di ”tropical-like cyclones” nel Mediterraneo, anche noti come Medicane, facendo uso di simulazioni numeriche del modello WRF (versione 4.1). Le simulazione numeriche sono state effettuate usando il supercomputer Cheyenne dell’NCAR-Wyoming Supercomputing Center (NWSC) e inizializzate con i dati di ERA5, l’ultima generazione di reanalisi meteorologiche dell’ECMWF. Questi casi, che sono stati recentemente analizzati nell’articolo di Miglietta e Rotunno (2019), sono stati riconsiderati qui per porre l’attenzione sull’origine dell’aria umida nei bassi strati atmosferici che precondiziona favorevolmente l’ambiente dove i cicloni si sviluppano. Nel primo Medicane erano presenti alti valori di umidità nei bassi strati atmosferici già prima che il ciclone si formasse, a causa degli intensi flussi superficiali dal mare nel Mediterraneo meridionale, associati ad aria secca e fredda proveniente dai Balcani orientali. Il secondo Medicane si intensifica fortemente nel momento in cui beneficia degli intensi flussi superficiali dal mare generati dall’irruzione dei venti di Tramontana e Cierzo vicino alla zona di formazione del ciclone. Benché limitati a questi due casi studio, i risultati delle simulazioni e dei test di sensibilità hanno identificato differenti condizioni ambientali favorevoli all’intensificazione dei Medicane nel Mediterraneo occidentale e meridionale, e dimostrano perché queste due aree sono considerate come hot spot per la formazione di questi fenomeni. Inoltre, è stato analizzato il ruolo dell’intrusione di aria secca d’alta quota nello sviluppo dei cicloni. Sono stati effettuati test di sensibilità dove è stata posta una condizione di minimo valore di umidità relativa (50%) nelle condizioni iniziali e nelle condizioni al contorno. Per entrambi i casi, è stato trovato che l’aumento di umidità ha l’effetto di anticipare la formazione del ciclone, producendo vortici più intensi e duraturi

Applications of regional ocean Ensemble Kalman Filter data assimilation

Data assimilation has been widely used in the forecast of oceanic states and tropical cyclones. In this thesis, the Ensemble Kalman Filter (EnKF) based data assimilation algorithm is applied to two applications, a regional ocean data assimilation system for the South Australian Sea and a coupled ocean-atmosphere tropical cyclone (TC) forecast system. The regional ocean data assimilation system consists of the data assimilation algorithm provided by the NCAR Data Assimilation Research Testbed (DART) and the Regional Ocean Modelling System (ROMS). We describe the first implementation of a physical balance operator (temperature-salinity, hydrostatic and geostrophic balance) to DART, to reduce the spurious waves which may be introduced during the data assimilation process. The effect of the balance operator is validated in both an idealised shallow water model and the ROMS model real case study. In the shallow water model, the geostrophic balance operator eliminates spurious ageostrophic waves and produces a better sea surface height (SSH) and velocity analysis and forecast. Its impact increases as the sea surface height and wind stress increase. In the real case, satellite-observed sea surface temperature (SST) and SSH are assimilated in the South Australian Sea with 50 ensembles using the Ensemble Adjustment Kalman Filter. Assimilating SSH and SST enhances the estimation of SSH and SST in the entire domain, respectively. Assimilation with the balance operator produces a more realistic simulation of surface currents and subsurface temperature profile. The best improvement is obtained when only SSH is assimilated with the balance operator. A case study with a storm suggests that the benefit of the balance operator is of particular importance under high wind stress conditions. Implementing the balance operator could be a general bene t to ocean data assimilation systems. The TC forecast system consists of DART and coupled ROMS - WRF (the Weather Research Forecast model). High-frequency (HF) radars can provide high-resolution and frequent ocean surface currents observations during the TC landfall. We describe the first assimilation of such potential observations using idealised Observing System Simulation Experiments. In this system, synthetic HF radar observed coastal currents are assimilated and the forecast performances for weak (Category 2) and strong (Category 4) TCs are examined. Assimilating coastal surface currents improves the 24-hour forecasts of both intensity and track. For the strong case, the errors of the maximum wind speed (Vmax) and the integrated power dissipation (IPD) forecast reduce up to 50%. For the weak case, the improvements in Vmax and IPD forecast are lower (20%), but the track forecast improves 30%. These improvements are similar to the magnitude of the current operational TC forecast error, so that assimilating HF radar observations could be a substantial benefit.Open Acces

Sting jets in simulations of a real cyclone by two mesoscale models

The existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized However, there are still very few published studies on the subject Furthermore, although ills known that other models are capable of reproducing sting jets, in the published literature only one numerical model [the Met Office Unified Model (MetUM)] has been used to numerically analyze these phenomena This article alms to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets A sting jet event during the passage of a cyclone over the United Kingdom on 26 February 2002 has been simulated using two mesoscale models namely the MetUM and the Consortium for Small Scale Modeling (COSMO) model to compare their performance Given the known critical importance of vertical resolution in the simulation of sting jets the vertical resolution of both models has been enhanced with respect to their operational versions Both simulations have been verified against surface measurements of maximum gusts, satellite imagery and Met Office operational synoptic analyses, as well as operational analyses from the ECMWF It is shown that both models are capable of reproducing sting jets with similar, though not identical. features Through the comparison of the results from these two models, the relevance of physical mechanisms, such as evaporative cooling and the release of conditional symmetric instability, in the generation and evolution of sting jets is also discusse