Thermally-driven Mesoscale Flows and their Interaction with Atmospheric Boundary Layer Turbulence

169 Pages·2020·7.949 MB·English

by  Jon Ander Arrillaga Mitxelena

Springer Theses
Recognizing Outstanding Ph.D. Research
Jon Ander Arrillaga Mitxelena
Thermally-driven
Mesoscale Flows and
their Interaction with
Atmospheric Boundary
Layer Turbulence
Springer Theses
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Jon Ander Arrillaga Mitxelena
Thermally-driven Mesoscale
Flows and their Interaction
with Atmospheric Boundary
Layer Turbulence
Doctoral Thesis accepted by
Universidad Complutense de Madrid, Spain
123
Author Supervisors
Dr. Jon AnderArrillaga Mitxelena Prof. JordiVilàGueraudeArellano
Departamento deFísica delaTierra y Meteorology andAirQuality Group
Astrofísica Wageningen University
Universidad Complutense deMadrid Wageningen,The Netherlands
Madrid,Spain
Prof. Carlos Yagüe
Departamento deFísica delaTierra y
Astrofísica
Universidad Complutense deMadrid
Madrid,Spain
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-48578-8 ISBN978-3-030-48579-5 (eBook)
https://doi.org/10.1007/978-3-030-48579-5
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’
Supervisors Foreword
The main objective of the thesis carried out by Jon A. Arrillaga and defended in
January2019atthe Complutense University ofMadrid(Spain),was to advance in
the knowledge of the physical processes that take place in the interaction of
thermally-driven mesoscale flows (mainly sea breezes and mountain breezes) with
boundary-layer turbulence. This is an important question as was highlighted in the
lastinternationalSymposiumonBoundaryLayersandTurbulenceheldin2018and
organised in Oklahoma (USA) by the American Meteorological Society, where
Jon A., as a Ph.D. student participated and won the Outstanding Student Poster
Presentation. The novelty of his research lies in the simultaneous analysis of
mesoscale fluxes (with a characteristic spatial scale between 10 and 100 km) with
atmospheric turbulence (with a maximum characteristic scale of 1 km). As a con-
sequence of this combined analysis, different atmospheric regimes have been
identified during his Ph.D. thesis in the transition of turbulence dominated by
convection and turbulence dominated by shear. This result isvery relevant since it
allows already a better understanding of the interaction between mesoscale flows,
explicitly resolved in numerical models, with the parameterization of turbulence
under the different mechanical and convective regimes. As such, this research
provides observational and numerical evidence on phenomena that occurs in the
gray zone (the scales ranging from hectometres to 5 km).
To carry out his work, Jon A. Arrillaga designs a methodology that combines
observations with systemic numerical experiments. Jon A. has been actively
involved in collecting these observations, and in performing high-resolution
numerical simulations carried out with the WRF mesoscale prediction model. The
work covers three study locations of different complexities: The Cantabrian Coast
in the Basque Country (Spain), the relative topographically flat region around the
213-mmeteorologicaltowerofCabauw(TheNetherlands),andthesurroundingsof
La Herrería Forest, nearby Guadarrama Mountains (Madrid, Spain). These three
locations,characterisedbydifferentlandusesandtopography,provideawiderange
ofpossibilitiesregardingthetypeofinteractionbetweenthestudiedbreezesandthe
turbulence in the atmospheric boundary layer. A key new finding of the Ph.D. has
been the development of an algorithm that allows to discern and isolate the sea
v
vi Supervisors’Foreword
breeze and the nocturnal katabatic flow from the synoptic scales (>100 km),
mesoscales and boundary-layer scales. The algorithm has been developed satis-
factorilyinthethreesitesreferenced aboveanditwillbeusedinfuturestudiesfor
the discrimination of scales in atmospheric phenomena, for both observations and
numerical results.
TheThesisiscomposedoffourchaptersofresults.Chapter3studiessea-breeze
events in a complex area such as the Cantabrian Coast. Analyses of observations
gathered in two stations during one summer are used for this purpose. The
observational analysis showsthefrequencyoftheseeventsatthistime ofyear and
the consequences of the arrival of the sea-breeze front on the temperature and
humidity.Thedetailedtreatmentoftheobservationsisusedtostudywhichaspects
of the numerical simulations are still not able to reproduce the main sea-breeze
features. Chapter 4 analyses 10 years of data from the 213-m meteorological
observatory (as part of the Ruisdael Observatory https://ruisdael-observatory.nl/)
and combines surface observations with upper-atmospheric measurements,
including boundary-layer depth. One of the main findings is that the arrival of the
sea breeze accelerates the afternoon transition, i.e., the transition from the con-
vectivetostableboundary-layerconditions.Insomecasestheconvectiveboundary
layercollapsesduetothefrontalpassage,producingasaconsequenceasignificant
variability of gases such as the CO and radon-222. Chapter 5 connects this
2
observational study with high-resolution numerical simulations to determine the
abilityofnumericalweathermodelstoreproducetheseabreeze.Onlyaround30%
of the observed sea-breeze events are reproduced by the model, and the use of the
selectionalgorithmreflectstheroleofthedifferentatmosphericscalesinexplaining
the biases. The final chapter (Chap. 6), investigates a new observational network
(Guadarrama Monitoring Network, GuMNet: www.ucm.es/gumnet) in Spain,
developedbytheMoncloaCampusofInternationalExcellenceinthesurroundings
of La Herrería Forest. Here, Jon A. Arrillaga studied how thermally-induced
downslope winds influence turbulence and the transport of CO . Jon A. Arrillaga
2
concluded that depending on the onset of weaker or stronger downslope winds,
there is a respective transition to a strongly or weakly stable nocturnal boundary
layer, influencing at the same time the evolution of CO . The originality of the
2
study relies on its interdisciplinarity. It is shown that to understand and model
greenhouse gases like CO , it is key to reproduce satisfactorily the interaction
2
between mesoscale flows and local turbulence.
In conclusion, the quality of this Thesis is supported by the associated 4 publi-
cations in high-impact journals, as well as the numerous presentations at interna-
tionalconferencesheldduringthe4yearsofhisPh.D.,whereJonA.obtainedsome
prestigiousprizes:OutstandingStudentPosterAward(EGU2015,Vienna,Austria),
Supervisors’Foreword vii
StudentHonourableMention(BLTSymposium2016,SaltLakeCity,USA),Young
ScientistTravelAward(EMS2017,Dublin,Ireland),GraduateStudentAward(UC
Davis Air Quality Research Center MAC-MAQ 2017, USA), Outstanding Student
Poster Presentation(BLT2018, Oklahoma City, USA).
Wageningen, The Netherlands Prof. Jordi Vilà Guerau de Arellano
Madrid, Spain Prof. Carlos Yagüe
April 2020
Abstract
Introduction
Atmospheric motions are classified according to their spatial and time scales from
largesttosmallestintomacroscales,mesoscalesandmicroscales.Amongmesoscale
motions,wefindthethermally-drivenflows,whicharedrivenbyhorizontalthermal
contrasts in scales between around 1 and 100–200 km, and occur in the form of
closed circulations. They have a critical role in transferring energy between the
macroscales and microscales. In this thesis, we investigate sea breezes (SBs) and
mountain breezes (MBs). Apart from being ubiquitous, they play a fundamental
role in the complex turbulent decay during the afternoon and evening transition
(AET) of the atmospheric boundary layer (ABL). Intimately linked with the
interaction between mesoscale flows and ABL turbulence, relevant scalars such as
CO canalsobesignificantlyaffectedbytheonsetofthermally-drivencirculations.
2
Mesoscale models such as Weather Research & Forecasting (WRF) have shown
deficienciesinreproducingtheturbulentdecayduringtheAETandtheinfluenceof
mesoscale flows on the CO budget.
2
Objectives
The main objectives of this thesis can be outlined in the following bullet points:
(cid:129) Analysing the large-scale and local forcings influencing the formation of
thermally-driven flows, and developing an objective algorithm to select the
mesoscale events.
(cid:129) Toshedlightontheinterconnectionsbetweenthermally-drivenflowsandABL
turbulence during the AET.
(cid:129) QuantifyingtheimpactofmesoscaleflowsonthedynamicsoftheABLandthe
associated variability in CO and 222Rn.
2
(cid:129) ToevaluatetheperformanceoftheWRFmodelinsimulatingthecharacteristics
of SB phenomena and their interaction with ABL turbulence during the AET.
ix
x Abstract
Data and Methodology
Theresearchstrategyfollowedinthisthesiscombinesobservationalmeteorological
databasesandnumericalsimulationsfromtheWRFmesoscalemodel.Wefocuson
three observational sites, each of them representing a distinct scenario for the for-
mationofthermally-drivencirculations:theBasqueCoast(Spain)toanalysetheSB
overcomplexterrain;theCESARsite(Netherlands),whereweexploretheSBover
flatterrain;andLaHerreríasite(Spain),toinvestigatekatabaticwindsnearbyasteep
mountainous slope. The model adds a spatial insight not provided by the observa-
tions and allows to evaluate its performance in reproducing the thermally-driven
winds. Furthermore, one of the key aspects of this thesis is the development of a
systematic algorithm based on objective criteria to select mesoscale events and
produce robust statistics.
Results
First, we characterise SB phenomena at the Basque Coast by comparing observa-
tions from two topographically contrasting sites. Numerical simulations from the
WRF model provide a more precise insight, and allowus to evaluate the influence
of the SB onset on atmospheric variables and the associated turbulence.
The investigation of SB phenomena is continued with the analysis of a 10-year
observational database from the CESAR site. After applying the mesoscale selec-
tion algorithm, we analyse 102 SB days taking place at different times along the
AET,andweclassifythemaccordingtothesurface-turbulenceconditions.Wefind
that the impacts of SB flows on the ABL dynamics and its thermal structure are
contrasting depending on the encountered turbulent characteristics. Our findings
furthermorerevealthedeterminantroleoftheSBdirectioninthetransportofwater
vapour,CO and222Rn.NumericalsimulationsfromtheWRFmodelspanningthe
2
same 10-year period are employed to analyse its performance in reproducing the
main characteristics of the SB, their influencing factors and the impact on ABL
turbulence during the AET. We find that the sensible-heat flux is greatly overes-
timated, and probably as a consequence, the simulated SB intensity is magnified.
Finally,theroleofkatabaticflowsinthedynamicsandturbulentfeaturesofthe
SBL is explored by employing observations from La Herrería site. Forty katabatic
events are selected from a summer database by using the mesoscale selection
algorithm. We find a direct relationship between the maximum intensity of the
katabatic flows and the turbulent characteristics of the SBL. By relating the
dynamics of the SBL regimes with the CO budget, we estimate the contribution
2
of the different forcings in the variability of this greenhouse gas.