PALESTRA 1:
PhD. David R. Fitzjarrald
ASRC/SUNY, EUA
Title: Synthesis and analysis in atmospheric boundary layer data studies
(Síntese e Análise nos estudos da camada limite atmosférica)
Abstract:
Synthesis. Researchers are currently exhorted to link many observational
findings, an effort to find grand overall patterns, a process of synthesis. This
brings calls for regularizing datasets, to ‘fill gaps’ inevitable for in situ
measurements. It also inspires authors to make ever-grander claims of ‘global
significance’.
Analysis. A dwindling number of scientists who go outdoors to perform field
experiments take the opposite path, in the process of analysis. One example
would be to ask how we learn about the fundamental processes of surfaceatmosphere exchange by examining phenomena that promote turbulence at the
interface, examining event-based composites, for example. The approach
inspires authors to claim they’ve gained ‘universal’ understanding’ of complex
processes, such as turbulence.
These two approaches conform in part to the thinking of Heraclitus of Ephesus
(Heráclito de Éfeso), the pre-Socratic Greek philosopher:
"No man ever steps in the same river twice"
“Nenhum homem jamais passa no mesmo rio duas vezes.”
"The path up and down are one and the same".
“O caminho para cima e o caminho para baixo são iguais.”
No observation a list questions one intent behind the first quote—things change;
nature doesn’t perfectly repeat. The second ‘truth’ is surely true if one argues
that the aims of the paths up (synthesis) and down (analysis) are to foster better
understanding of nature. Are the approaches equally valuable? Or perhaps we
err in each case in the premature pursuit of greatness, a known frailty of human
nature?
Some discussion points:
Observation is always conditional sampling.
When examining remotely sensed data, one may really be concentrating on a
few seconds of information per day at a site, when the sensor is at nadir (polar
orbiter) or is available at infrequent intervals or at limited spatial resolution,
conditioning the sample and calling for continuity assumptions.
Confirmation is essential for progress, but it is not discovery. We must recognize
that the ideal conditions required for some of our cherished similarity
hypotheses lead us to condition our observations to particular environments.
Is there a future for atmospheric scientists in field observation? Will robots,
perhaps assisted by technicians, perform field observations in the future? (Can
scientists still learn from personal experience in the field?)
Case study question, to guide the discussion:
Do forests warm or cool the regional climate?
Fazem florestas o clima regional quente ou frio?
PALESTRA 2:
PhD. José D Fuentes
Penn State University, EUA
Title: Transport and chemistry of plant-emitted gases in the central
Amazonia
Abstract: This presentation will provide an overview on the salient features of
the transport and the chemistry of the gases emitted by the rainforest in the
central Amazonia. Results, obtained as part of a field campaign during 2014,
will be presented and discussed. Chemical species and their ambient
concentrations within and above the forest were investigated throughout the
course of ten months. The rainforest emits sufficient amounts of reactive
hydrocarbons such as isoprene and monoterpenes to provide precursors of
secondary organic aerosols and cloud condensation nuclei. Mesoscale
convective systems transport ozone from the middle troposphere, regionally
enriching the atmospheric boundary layer and the forest canopy. Following
storms, ozone levels remained enhanced for about two hours and initiated
chemical reactions involving rainforest-emitted gases and ozone, producing
substantial yields of hydroxyl radicals which further contributed to the oxidation
of hydrocarbons. The field studies combined with numerical modeling
investigations revealed that mesoscale connective storms modulate the
chemical cycles that lead to the formation of secondary aerosols that serve as
the cloud condensation nuclei necessary for the formation of clouds.
PALESTRA 3:
PhD. Otávio Costa Acevedo
UFSM - Brasil
Titulo: Diferentes aspectos da camada limite estável: observações e
modelagem
Resumo: Serão apresentadas as diferentes linhas de pesquisa em camada
limite noturna desenvolvidas pelo Grupo de Micrometeorologia da UFSM. Estas
envolvem a estrutura vertical da camada limite e os balanços de energia
cinética turbulenta e fluxo de calor em condições de desacoplamento e
acoplamento entre a superfície e níveis superiores da atmosfera. Estes
aspectos serão analisados observacionalmente e do ponto de vista de
modelagem com esquemas numéricos simplificados. Os processos de
transferência noturna de escalares entre superfícies vegetadas e a atmosfera
no período noturno serão abordados com foco na região Amazônica. Nesta
parte será mostrado o papel de processos de baixa frequencia nos fluxos
noturnos totais entre a superfície e a atmosfera. Também serão analisados
aspectos operacionais associados à previsibilidade de quantidades no período
noturno por modelos numéricos de mesoescala. Ao final serão mostradas as
perspectivas futuras de medidas detalhadas da camada limite atmosférica pelo
grupo da UFSM.
PALESTRA 4:
PhD. Jielun Sun
NCAR, EUA
Title: ‘The Role of Large-Coherent-Eddy Transport in the Atmospheric
Surface Layer Based on CASES-99 Observations’
Abstract: The analysis of momentum and heat fluxes from the Cooperative
Atmosphere-Surface Exchange Study in 1999 (CASES-99) field experiment is
extended throughout the diurnal cycle following the investigation of nighttime
turbulence by Sun et al. Based on the observations, limitations of MoninObukhov similarity theory (MOST) are examined in detail. The analysis
suggests that strong turbulent mixing is dominated by relatively large coherent
eddies that are not related to local vertical gradients as assumed in MOST. The
HOckey-Stick Transition (HOST) hypothesis is developed to explain generation
of observed large coherent eddies over a finite depth and the contribution of
these eddies to vertical variations of turbulence intensity and atmospheric
stratification throughout the diurnal cycle. The HOST hypothesis emphasizes
the connection between dominant turbulent eddies and turbulence generation
scales, and the coupling between the turbulence kinetic energy and the
turbulence potential energy within the turbulence generation layer in
determining the turbulence intensity. For turbulence generation directly
influenced by the surface, the HOST hypothesis recognizes the role of the
surface both in the vertical variation of momentum and heat fluxes and its
boundary effect on the size of the dominant turbulence eddies.
PALESTRA 5:
PhD. Nelson Dias
UFPR - Brasil
Título: ‘O Fenômeno de Hurst em Turbulência Atmosférica: memória de
longo prazo, e a (in)existência de escalas integrais’
Resumo: O Fenômeno de Hurst, caracterizado por dependência de longo
tempo em séries temporais, e primeiramente identificado em séries geofísicas
de vazão, nível d'água, precipitação e temperatura, é identificado em
numerosos blocos de medições micrometeorológicas de turbulência realizadas
em 3 sítios micrometeorológicos distintos. O fenômeno é mais intenso para
variáveis de ordem 1 (flutuações de velocidade longitudinal, velocidade vertical
e temperatura), mas também afeta variáveis de ordem 2 (covariâncias entre as
componentes longitudinal e vertical, e entre a velocidade vertical e a
temperatura). Tanto a variável original proposta por Hurst, denominada
"alcance renormalizado" ("rescaled range") quanto uma nova variável
recentemente associada ao erro aleatório da média do bloco exibem o
fenômeno de Hurst, embora com coeficientes de Hurst ligeiramente diferentes.
O fenômeno de Hurst é equivalente nos casos analisados à inexistência da
escala integral da turbulência, e leva a estimativas majoradas de erro de
medição da média do bloco em comparação com as estimativas de erro
baseadas na existência da escala integral.
PALESTRA 6:
PhD. Marcelo Chamecki
Penn State University, EUA
Título: ‘A estrutura local da turbulência na região inferior da camada limite
atmosférica’
Resumo: A busca por modelos adequados que representem a distribuição de
energia cinética turbulenta (ECT) por escala é um dos desafios teóricos e
aplicados no estudo de escoamentos turbulentos. As previsões de Kolmogorov
para a região inercial formam um dos pilares da teoria de turbulência. No
entanto, na maioria dos problemas aplicados, as escalas da região de
produção de ECT tem um papel mais importante do que as escalas da região
inercial. Para escoamentos próximos a paredes (escoamentos em canais e
camadas-limite sem estratificação térmica), existe uma teoria baseada em
análise dimensional que prevê o comportamento do espectro de energia ou da
função de estrutura na região de produção. Nessa apresentação, os avanços
mais recentes dessa teoria serão revisados e estendidos para dois
escoamentos de importância prática em micrometeorologia: a camada limite
superficial e a sub-camada rugosa acima de um dossel. Dados medidos em
campo e produzidos por simulações de grandes vórtices serão utilizados para
verificar a aplicabilidade dos resultados teóricos para esses escoamentos.
PALESTRA 7:
PhD. Luca Mortarini
CNR, Itália
Title: ‘New findings on low-wind and meandering’
Abstract: The investigation of low-wind cases measured during the Urban
Turbulent Project campaign (Torino, Italy), the Large-Scale BiosphereAtmosphere Experiment (Amazonia, Brazil) and in the Santa Maria
meteorological tower (Santa Maria, Brazil) are presented to give some insight
on the wind meandering phenomenon, i.e. the large, non-turbulent oscillations
of the horizontal wind velocity and temperature. Through the analysis of the
Eulerian auto-correlation functions and spectra meandering and not meandering
cases are identified and their properties compared.