Observación y análisis de la atmósfera

Presentación del tema: "Observación y análisis de la atmósfera"— Transcripción de la presentación:

1 Observación y análisis de la atmósfera
Curso de Posgrado: Fundamentos de la Variabilidad Climática Global y en Sudamérica Clase 1: Observación y análisis de la atmósfera Formas de descripción de la circulación: promedios Conceptos meteorológicos: Descripción espacial de las variables meteorológicas Balance de viento geostrófico y de viento térmico Balance de calor en la atmósfera Descripción bidimensional de la circulación atmosférica media Ciclo de energía Carolina Vera CIMA-DCAO, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires CONICET-UMI3351/CNRS

2 Bibliografía Hoskins, B. J. and R. P. Pearce, 1983: Large-Scale Dynamical Processes in the Atmosphere. Academic Press James, I. N., 1994: Introduction to Circulating Atmospheres. Cambridge Atmospheric and Space Science Series. Peixoto, José, and Abraham H. Oort, 1992: Physics of Climate. American Institute of Physics.

3 Sistema de Observaciones Global
The scientists in atmospheric scientists are blessed among scientists in that many thousands of high quality of observations are made for them across the globe, from the surface to the stratosphere. These observations are taken by trained observers or by automatic platforms in order to provide operational meteorological information, to diagnose the current state of the atmosphere and as input for the numerical forecast models. As a spin off, these observations, archived, quality controlled and analyzed, form an important data base for the scientific study of the atmosphere. This picture shows an example of the observations received at ECMW on a particular day. CONVENTIONAL OBSERVATIONS Since the conventional data report the values in the same units as the model variables, and on pressure or height levels, they can be used more or less directly by the analysis system after vertical interpolation. Reports of pressure and humidity are used from SYNOP (conventional surface weather station reports). 10 meter wind observations are not used, not even from marine locations such as coastal stations or minor islands. Pressure and winds are used from SHIP (conventional weather reports from moving ships) and DRIBU (drifting buoys). Temperature, wind and humidity from TEMP (upper air observations from radio sonde stations) are used and their position defined according to the pressure at all reported levels. Temperatures in the stratosphere are corrected for estimated mean errors (bias correction). Humidity observations from drop sondes are not used. Winds from PILOT (wind measurements in the free atmosphere from stations launching balloons) are used, except when there is duplicates with radio sonde data. PROFILERS (measuring winds with remote sensing) provide wind speed and direction at very high temporal resolution. Temperature and wind reports are used from AIREP (manual air craft reports), AMDAR (Aircraft Meteorological Data Relay) and ACARS (automatic air craft reports). The traditional AIREP observations now only account for ~4% of all used aircraft data, as most commercial aircrafts operate the AMDAR or ACARS systems. During landing and take-off the latter provide data in quantity, quality and location comparable to radio sondes. PAOB is a hybrid between conventional and satellite data. They are manually derived pseudo-observations of MSLP on the Southern Hemisphere, made by the Australian Bureau of Meteorology from satellite images. Humidity observations reported as relative humidity or dew point, are transformed into specific humidity using the reported temperature. SYNOP dew points are used, together with the temperature to calculate the 2 m specific humidity. Other data types are used to analyse snow, ice, SST, soil wetness and ocean waves. These are at present analyzed separately, but might in the future be incorporated in the full data assimilation system. 24h summary of observations received at ECMWF, 5 July 2004

4 UPPER-AIR OBSERVATIONS
RADIOSONDES

5 UPPER-AIR OBSERVATIONS
AIRCRAFTS

6 UPPER-AIR OBSERVATIONS GEOSTATIONARY SATELLITES
Since 1979 there has been a significant increase in the quantity, quality and diversity of satellite observations. At the time of writing (autumn 2003) ECMWF routinely receives data from more than 15 satellites, some of which are equipped with several instruments that provides in total 28 satellite data sources. Consequently there is now a strong benefit from satellite data in the ECMWF and the influence of other conventional data types are becoming less critical. In particular over the Southern Hemisphere, where there is a lack of conventional data, satellite data has had a large impact on the scores which are now almost as good as in the Northern Hemisphere. However there are limitations in the use of satellite data over land surfaces. Over desertic areas and frozen regions, at the state of the art, is particularly difficult to use tropospheric channels due to the inaccurate knowledge of the underlying surface emissivity. On global scale these are areas were overall we assimilate less data. DIFFERENT SATELLITES There are two types of a satellites, geostationary and low earth orbiting satellites. Geostationary satellites are positioned in the earth's equatorial plane at about km height. They have a wide spatial coverage and high temporal resolution (observations up to every few minutes). Due to their position they cannot cover the whole planet and in particular not the polar regions. Due to the high altitude they do not measure in the micro wave spectrum at present. SATELLITE PASSIVE MEASSUREMENTS Atmospheric parameters can be measured by passive technologies through sensing natural radiation emitted by the earth and atmosphere, or solar radiation reflected by the earth and atmosphere. Most current satellite data originate from this approach. Radiances are provided by several satellites (the orbiting NOAA 15, 16 and 17, and the geostationary Meteosat 5 and 7, and GOES 9, 10 and 12). For regions with clear sky the radiances provide information on temperature and moisture content in broad layers. However, when clouds are present, no attempt is made to determine temperature and moisture. Instead the radiances are used to derive atmospheric motion vectors (previously known as cloud winds or SATOB). Two MODIS (Moderate Resolution Imaging Spectroradiometer) instruments, the first launched on 18 December 1999 on board the Terra Platform, the second on 4 May 2002 on board the Aqua platform, are uniquely designed. They have a wide spectral range, high spatial resolution, and near daily global coverage to observe and monitor these and other changes of the earth's surface. Ozone total column and profiles are measured by the ENVISAT and NOAA satellites by agencies such as KNMI and DRL. SATELLITE ACTIVE MEASSUREMENTS Atmospheric variables can also be measured by active technologies which transmit radiation towards the earth and then sense how much is reflected or scattered back. This is done for the so called Seawinds (on board the QuickScat satellite) on the ERS-2 scatteometer providing wind vector information derived from the influence of the ocean capillary waves on the back scattered signal. Depending on the frequency of the radar, the data may be affected by the presence of rain (seawinds) or not (ERS-2).

7 UPPER-AIR OBSERVATIONS
ORBITING SATELLITES Low earth orbiting satellites circle the earth at heights between 400 and 800 km. They are able to cover the whole spectrum, including the micro wave band. But since it takes several days before the satellite comes back to the same point it needs many orbits to provide a full coverage of the globe. A constellation of 2-4 platforms is therefore necessary to ensure reasonable temporal sampling.

8 SURFACE OBSERVATIONS SURFACE STATIONS

9 SURFACE OBSERVATIONS SHIPS

10 SURFACE OBSERVATIONS BUOYS

11 Tropical Atmosphere-Ocean Array

12 Sistema de Análisis - Pronóstico
Predicciones numéricas del tiempo requieren de condiciones iniciales Observaciones de la Atmósfera y los Océanos irregularmente distribuidas en tiempo y espacio Análisis Meteorológico: Subjetivo Objetivo (métodos dinámicos-estadísticos que combinan las observaciones a partir de un campo preliminar)

13 Las variables atmosféricas están representadas en matrices que describen la estructura horizontal de la atmósfera. Resolucion media (NCEP/NCAR reanalysis: 2.5x2.5, NCEP/CFSR menos de 1x1) La escala vertical está representada en varios niveles.

14 ANALYSIS DATASET FOR CLIMATE STUDIES
Sistema de Asimilación de Datos … 00UTC UTC UTC … Observation collection Observation quality control 3- dimensional analysis Numerical forecast Observation collection Observation quality control 3- dimensional analysis Numerical forecast Observation collection Observation quality control 3- dimensional analysis Numerical forecast 3- dimensional analysis 3- dimensional analysis 3- dimensional analysis ANALYSIS DATASET FOR CLIMATE STUDIES

15 Base de datos: “Re-análisis”
Los análisis operacionales son afectados por cambios en los modelos, en las técnicas de análisis objetivo, asimilación y en los datos usados. Ellos tambien solo pueden hacer uso de aquellos datos que están disponibles en tiempo real. Esto afecta el monitoreo del clima ya que tales cambios planeados para mejorar el pronostico a corto plazo, producen cambios aparentes en el cima. Cantidades fundamentales tales como la intensidad de la celda de Hadley han cambiado con los años como el resultado de los cambios en los sistemas de asimilación de datos. Las bases de datos de re-analisis se construyen con sistemas de asimilación de datos de última generación “congelados” e incluyendo la mayor cantidad de observaciones disponibles y con mejores técnicas de control de calidad. NCEP-NCAR reanalyses (1948-continúa), NCEP CFSR reanalyses (nueva versión) ECMWF reanalyses: ERA 40 ( ), ERA Interim (nueva versión)

16 Zonal mean number of all types of observations per 2
Zonal mean number of all types of observations per 2.5degree lat-lon box per month in the NCEP reanalyses. A 12-month running mean has been applied (Kistler et al 2001, BAMS)

17 Observación y Modelado de la Atmósfera
Descripción de la circulación general  requiere  campos 3-dimensionales de las variables atmosféricas Necesidad de promediar: Promedios zonales Promedios verticales Promedios temporales Promedios de conjuntos (Composiciones) This first lecture is mainly intended for those students that have no background on the subject. So we will briefly review today how we deal with the huge amount of data available for the study of the atmospheric circulation, how observations are taken and collected and how they are synthesized. By the end of this lecture we will discuss the distribution of the heating that drives the atmospheric circulation and also discuss some aspects of the mean conditions.

18 Promediando la Atmósfera Promedio temporal
Necesidad de períodos temporales largos (Espectro de energía en la atmósfera: rojo o markoviano) Promedios de conjuntos o composiciones Fuerte variación estacional de la circulación (Promedios estacionales) Variaciones interanuales The average with respect to time is the most frequently used. Being the mean and the transient part of Q denoted in this way. If the temporal period, tau, is sufficiently long the time mean value of Q will be independent of tayu.

19 Promediando la atmósfera
El clima medio a gran escala presenta variaciones dominantes en la dirección zonal (latitudinal) y vertical y en menor medida en la dirección meridional (longitudinal) Promedio Zonal Promedio vertical The description of the global circulation generally implies that some kind of averaging has been carried out. The flow is thought as consisting of a mean part, and a fluctuating or eddy part. It is also assumed that the average properties of the eddies may well affect the mean fields. There are a number of different ways of averaging atmospheric data, one of the most frequently used is the average with longitude or zonal average. The earliest studies of the general circulation were concerned with the zonal average as most of the atmospheric variables change much less in the zonal direction than they do in the vertical or in the meridional directions. Indeed the latitude of an observing site is probably the most important single factor in determining its climate. The zonal average of any scalar quantity Q is denoted [Q] and may be defined as: The deviation is variously called the eddy part or the zonal anomaly of Q and denoted Q*. It follows immediately that :

20 Conceptos meteorológicos básicos a tener en cuenta

21 Escalas espaciales Z: Alturas p: presión X: Longitudes -Y: Latitudes

22 Representación del viento
Z p: presión X u: componente en x o componente zonal , positiva hacia el E w: componente en z o componente vertical, es positiva en los ascensos Si la escala vertical es la presión, la componente vertical del viento se la designa con ω y es negativa en los ascensos Vector Viento -Y v: componente en y o componente meridional , positiva hacia el N

23 Balance de viento geostrófico
. A Fuerza de gradiente de presión . 1009 hPa . Fuerza de Coriolis 1006 hPa Hemisferio Sur (HS) . 1003 hPa N Aproximación válida: Lejos de superficie variaciones espaciales de presión no exhiben fuertes curvaturas Variaciones temporales de presión pequeñas 1000 hPa E B

24 Balance de viento geostrófico
Viento geostrófico surge del balance de la fuerza de presión y la de coriolis Viento de gran escala y lejos de superficie es en buena medida geostrófico A B Hemisferio Sur (HS)

25 Estructura vertical de la atmósfera y el viento
Sistema (x,y,p) Alturas geopotenciales Componentes del viento geostrófico en (x,y,p) Sur Norte Hemisferio Sur (HS)

26 Ejemplo

27 Estructura vertical de la atmósfera y el viento
Espesor de una capa atmosférica Viento Térmico N S E O Hemisferio Sur (HS)

28 Balance de viento térmico
Aire mas caliente Aire más frío Fza. de presión Fza. de coriolis Norte

29 Ejemplo (2/4/2004) Altura geopotencial en 500 hPa
Espesor de la capa 500hPa/1000 hPa Temperatura en 700 hPa Altura geopotencial en 1000 hPa

30 Balance de calor en la atmósfera

31 Atmospheric heating CLIMATE SYSTEM
Distribution of heating and cooling within the atmosphere drives the atmospheric circulation. We must distinguish between adiabatic changes of temperature, which may arise from vertical motions during which no heat enters or leaves the air, and changes which result from heat entering or leaving the air, associated with diabatic processes. Diabatic heating or just heating arises from a large number of processes. Ultimately, absorption of short wave radiation is the source of heating and emission of long wave radiation provides cooling. Exchanges of heat between the different components of the climate system, which includes the solid Earth, the oceans, and the cryosphere, as well as the atmosphere are important for driving the global circulation CLIMATE SYSTEM

32 Balance de radiación en la Atmósfera
Balance de radiación en función de la latitud Flujo de energía de radiación : Línea cortada: solar incidente Línea punteada: solar incidente absorbida Línea sólida: de onda larga saliente Variaciones geográficas de la radiación -> Variaciones de la temperatura -> Circulación General de la Atmósfera

33 Esquema de la variación vertical del flujo hacia debajo de radiación solar y del flujo neto hacia arriba de la radiación infrarroja en una atmósfera libre de nubes. La diferencia entre los flujos de energía radiante entrante y saliente en la atmósfera baja es balanceada por el transporte hacia arriba de calor por los movimientos atmosféricos

34 Most of the solar energy reaching the surface goes to evaporate water
Atmosphere cooling is mostly due to long wave radiation, that is affected by air moist and its cloudiness As the air circulates, it may rise, cool and become saturated. Water vapor condensation releases large amounts of latent heat Water vapor in the atmosphere acts as a means of storing heat which can be released later Exchanges of heat with the underlying surface, which may either be the ground or the ocean surface. The oceans for their huge heat capacity acts as reservoir of heat in the climate system. It is assumed that much of the memory of the climate system on timescales longer than a month or so is due to heat stored in the oceans Most of the solar energy reaching the surface goes to evaporate water. Because of the very large LH of evaporation of the water, and the fact that most of the surface is moist, very large amounts of heat can be taken up in this way. Measurements reveal that as much as 90% of the incident sunlight at the surface evaporates water. Water vapor in the atmosphere acts as a means of storing heat which can be released later. If it becomes saturated, water vapor condenses and may rain out of the air. This condensation releases large amounts of latent heat. Most of the cooling of the atmosphere is due to long wave radiation, though some heat can be extracted locally by contact with a colder underlying surface. The transmissions of long wave radiation through the atmosphere is highly variable, being affected by the humidity of the air and its cloudiness Most of the solar energy reaching the surface goes to evaporate water Atmosphere exchanges (sensible and latent) heat with the ground and ocean surface

35 Calor medio zonal DJF JJA ERA-40 Atlas
Measuring all these different processes is a formidable task, and certainly cannot be done routinely over the entire volume of the atmosphere. Therefore, the current way to estimate the atmospheric heating is through residual methods or through model parameterizations. This figure shows the zonal mean net heating obtained from the ERA 40 climatology. In such dataset heating data are derived from Forecast model outputs and thus they are affected by model parameterizations. Therefore this data although good for qualitative analysis, they are not reliable enough for quantitative analyses The heating is strong and fills the entire depth of the troposphere in the tropics, being the evidence of the deep cumulus convection releasing latent heating throughout the tropical troposphere, being the maximum in the summer hemisphere. Separate bands of relatively deep heating are found in the middle latitudes, associated with the active midlatitude synoptic systems that promote precipitation and release of latent heat. Away from the tropics there is heating near the ground that is dominated by the turbulent transport of heat out of the ground. Regions of cooling, occupy much of the middle and upper troposphere. ERA-40 Atlas

36 Descripción bidimensional de la circulación general de la atmósfera

37 Temperatura media zonal
DJF JJA

38 JJA Temperatura media zonal Circulación meridional media zonal
A comparison between the temperature and meridional circulation fields shows that the low-latitude Hadley circulation has ascent where the temperature is greatest, and descent where it is less. That circulation will generate kinetic energy, is termed as thermally direct. Thermally direct circulation is also seen at high latitudes and particular in the winter SH. On the other hand, in the midlatitudes, the mean meridional circulation is thermally indirect, called the Ferrel cell, which represents a sink of kinetic energy. The fact that the Hadley cell is confined to the tropics is related as you will see in Isidoro´s lecture to the rotation of Earth. Combination of angular momentum convervation and thermal wind balance crudely explains the limit of the Hadley cell poleward branch in coincidence with the presence of maximum zonal wind Hadley Cell Ferrel Cell ERA-40 Atlas

39 Circulación meridional medial zonal
DJF This figure shows the zonal mean meridional streamfunction circulation. Rising motion is seen in the tropics with maximum vertical velocity in the summer hemisphere, while descent is observed around 25-30degres in the winter hemisphere. Such an axisymmetric circulation is the most obvious response of the atmospheric flow to the net heating excess in the tropics and the deficit at high latitudes JJA ERA-40 Atlas

40

41 Jet subpolar o “eddy-driven Jet”
Viento zonal (u) medio zonal DJF Jet subpolar o “eddy-driven Jet” Jet Subtropical This figure clearly shows the presence of a winter zonal wind maximum in coincidence with the poleward branch of the Hadley cell, generally called the subtropical jet. The presence of a stronger maximum of zonal wind peaking at the stratosphere is evident in the mean circulation of the winter SH. To lowest order, the subtropical jet can be understood as being driven by angular momentum transport associated with the Hadley circulation The polar front jet (also referred to as subpolar jet or the eddy-driven jet), on the other hand, is driven by eddy fluxes associated with Rossby waves JJA ERA-40 Atlas

42 Ciclo de energía #1 (Lorenz)
Calentamiento diferencial Flujos medios de temperatura Conversión de energía Energía potencial del estado medio Energía cinética del estado medio Generación de energía Decaimiento por Fricción

43 Circulación media perspectiva estratosférica
Temperatura media zonal JJA Circulación meridional media zonal Viento zonal medio zonal