A54A-01
Modelling the climate of the last millennium in South America
A simulations performed with a coarse resolution ocean-atmosphere-vegetation-seaice climate model driven by observed external forcing is used to investigate the climate evolution of South America during the last millenium. Initial investigation of the South America climate revealed that both the Medieval Warm Period and the Little Ice Age could be identified in the surface temperature timeseries. It is not clear, however, that these warming/cooling scenarios induced substantial changes in the area covered by forest or grass. Our results also predicted that after the Industrial Revolution the area-averaged South American temperature anomalies is up to 1K warmer as compared to pre-industrial conditions. Moreover, there exist a reduction (augment) in forest (grass) fraction. These results will be compared with recent paleoreconstructions available.
A54A-02
Simulation of the Multivariate ENSO index (MEI) as a Markov Chain and estimation of its probability distribution
The objectives of this work are the simulation of the behavior of the Multivariate El Niño Southern Oscillation
Index (MEI) with the use of a Markov chain with six states. The estimation of the transition matrix was made using
observed values obtained from the monthly MEI time series of overlapped bi-monthly means reported by NOAA
since 1950; this data are available through the NOAA web page
(http:www.cdc.noaa.gov/people/klaus.wolter/MEI/table.html). With the values of the transition matrix it is possible
to test the hypothesis that the MEI series can be simulated using a Markov chain calculating the autocorrelation
function and the number of transitions among states in simulated ensembles and compared with the
corresponding calculated functions obtained using the observed data. The characteristics of the transition matrix
indicate that the process is very persistent given the time scale used and because the MEI series is smoothed.
The results do not allow to reject the hypothesis that the process could be simulated using a Markov chain. Then
we evaluate the probability of the state of the process after a given number of steps (months) to produce a
probabilistic forecasting for the MEI state several months in advance. We selected periods with MEI values
greater than 1, these represent the realization of ENSO events. With the values reached in these events we
estimate the probability for MEI values grater than 1 in steps of 0.25. This is the conditional probability of obtaining
grater MEI values once a MEI =1.00 was reached.
http:www.cdc.noaa.gov/people/klaus.wolter/MEI/table.html
A54A-03
The Relationship Between The Indian Ocean Dipole And The Observed Precipitation On The Onset Of The South American Monsoon System: A Correlation Analysis
The relationship between the Indian Ocean Dipole (IOD) and the South American precipitation anomalies observed during the Brazilian pre-rainy season (austral spring) is analyzed through a linear correlation analysis. The IOD can be represented by the Dipole Mode Index (DMI), defined as the difference between the normalized sea surface temperature (SST) anomalies observed in the western Indian Ocean (60°-80°E, 10°S-10°N) and in the eastern side of this basin (90°-110°E, 10°S- 0°). In this way, warmer SST in the western Indian and colder in the eastern Indian define a positive DMI and are observed during positive IOD events. The opposite characteristics occur during the negative IOD episodes. The analysis is made for the period between 1950 and 2003 and correlations between the DMI and precipitation anomalies time series are elaborated in a seasonal and monthly scale. Negative correlations in the northeastern Brazil and positive over the southeastern South America were found for the austral spring. This result implies that during positive IOD events enhanced precipitation over the subtropics and drought conditions over northeastern Brazil may occur. In a monthly analysis, this dipolar structure is more evident during October and November while there are not statistically significant correlations over the continent in September. In October, negative correlations occur in some parts of southeastern Brazil while positive is observed over the southeastern South America. This dipolar structure is displaced northward during November when negative correlations over northeastern Brazil and positive over the Parana Brazilian State are observed. A lag correlation analysis suggest that the SST anomalies observed in the Indian Ocean since July has some relationship with the precipitation anomalies observed in the continent during October and November. In order to explain the dynamical aspects between the IOD episodes and the South American climate, numerical experiments with a general circulation model are being carried out and they will be presented elsewhere.
A54A-04
Gridded Fields of Monthly Temperature and Precipitation for North America
High-resolution gridded fields over spatially extensive regions are critical in understanding large-scale climatic variability and change. Gridded fields of monthly temperature and precipitation for North America were recently developed by NOAA's National Climatic Data Center (NCDC). Although they have many potential applications, the grids are primarily intended for operational climate monitoring applications, including the estimation of regional- scale temperature trends and the development of blended tree ring/in situ drought reconstructions. There were two steps in the creation of the temperature and precipitation fields. The first was the development of a high-quality dataset of historical (i.e., weather station) records, which were obtained from three sources: NCDC, Environment Canada, and Creighton University. The station records were subjected to a barrage of quality assurance reviews, such as time series checks for spurious changes in the mean and variance and neighbor checks to identify outliers from either a serial or spatial perspective. State-of-the-art homogeneity adjustments were also applied in the case of temperature. The second step entailed the actual gridding of the station data via climatologically aided interpolation (CAI). Gridded fields of station normals, an initial requirement for CAI, were produced via trivariate thin-plate smoothing spline models. Gridded fields of temperature and precipitation for each year/month were then created by interpolating station-based anomalies via a sophisticated inverse distance weighting scheme, then adding the gridded anomalies to the gridded normals. The efficacy of the gridded fields was assessed using a cross-validation scheme and withheld data points.
A54A-05
Evaluation of 20-min and Annual Radiation Budget Components and Cloudiness in a Mountainous Valley
Logan, Utah (USA) is among cities located in the mountainous valley in the western portion of Rocky Mountains in North America. It is the county seat of Cache Valley, a metropolitan area with a population of about 100,000. The valley had the polluted air in the USA during January 2004. To evaluate the daily and annual radiation budget and cloudiness in this mountainous valley, we set up a radiation station in the middle of the valley to measure the 20- min radiation budget components namely: incoming (Rso) and outgoing (Rso) solar or shortwave radiation, using to CM21 Kipp and Zonen (one inverted) and incoming (Rli) (or atmospheric) and outgoing (Rlo) or terrestrial) longwave radiation using two CG1 Kipp and Zonen Pyrgeometers (one inverted) during the year of 2003. All pyranometers and Pyrgeometers were ventilated with four CV2 Kipp and Zonen ventilation systems throughout the year to prevent deposition of dew, frost and snow, which otherwise would disturb the measurements. We also measured the 2-m air temperature and relative humidity along with surface temperature. All measurements were taken every 2 s, averaged to 20 min, continuously throughout the year 2000. A Met One heated rain gauge measured precipitation. Comparison of the annual radiation budget components indicates that about 25% of the annual Rsi (5848.6 MJ/ (squared m-y)) was reflected back to sky as Rso. Rli and Rlo amounted to 9968.7 and 13303.5 MJ/ (squared m-y)), respectively. This yielded about 1364.9 MJ/ (squared m- y)) available energy (Rn). Having the 2-m air temperature and moisture data and comparison between the theoretical and the measured longwave radiation, we evaluated the 20-m cloudy conditions throughout the year of 2003. The average cloud base height was 587 m (ranged from zero for foggy conditions to about 3000 m). Annual cloudiness contributed about 139.1 MJ/ (squared m-y)) more energy in this valley.
A54A-06
Atmospheric Turbulence Measurements With the Automatic Mini UAV 'M2AV Carolo'
The limitations of manned airborne meteorological measurements led to the development of an autonomously operating mini aircraft, the Meteorological Mini-UAV (M2AV), at the Institute of Aerospace Systems, Technical University of Braunschweig, Germany. The task was to develop, test and verify a meteorological sensor package as payload for an already available automatic carrier aircraft, the UAV 'Carolo T200', which operates autonomously i.e. without remote control. The M2AV is a self constructed model aircraft with two electrically powered engines and a wingspan of two meters. The maximum take-off weight is 4.5~kg (the M2AV is therefore classified as an model plane which simplifies authority issues), including 1.5~kg of payload. It is hand-launched which makes operation of the aircraft easy. With an endurance of approximately 50 minutes, the range accounts for 60 km at a cruising speed of 20~m/s. The M2AV is capable of performing turbulence measurements (wind vector, temperature and humidity) within the troposphere and offers an economic component during meteorological campaigns. The meteorological sensors are mounted on a noseboom to minimise the aircraft's influence on the measurements and to position the sensors closely to each other. Wind is measured via a small five-hole probe, an inertia measurement unit and GPS. The flight mission (waypoints, altitudes, airspeed) is planned and assigned to the aircraft before the semi- automatic launch. The flight is only controlled by the on-board autopilot system which only communicates with a ground station (laptop PC) for the exchange of measured data and command updates like new waypoints etc. The talk gives details on the technical items, calibration and first missions. Results from first field experiments like the LAUNCH-2005 campaign near Berlin are used for data quality assessment by comparison with simultaneous lidar and sodar measurements. An in situ comparison with the highly accurate helicopter-borne turbulence probe Helipod demonstrates that the wind vector can properly be measured by 20~Hz. Also recently obtained data from flights in katabatic flow over Mallorca island and at Halley station, Antarctica, will be presented.
A54A-07
Non-normal Perspectives on Jet Stream Dynamics
The Earth's mid-latitude jets and associated storm tracks constitute the most familiar and best observed of turbulent fluid systems as well as the most central to human comfort and commerce. Theoretical interest in turbulence as a phenomena and the practical utility of prediction of cyclogenesis and jet stream configuration have motivated efforts to understand both the deterministic dynamical evolution and the statistical properties of the jets and associated jet disturbances. Part of the fascination and challenge of understanding jet streams is that the jet disturbances arise from the jets and are steered by them while these same disturbances are themselves producing and maintaining the jets. It is commonly held that turbulent systems such as the mid- latitude jets are irreducibly complex in behavior but it turns out that in strong turbulence such as that of the jets there is emergent a particularly simple and orderly dynamics controlling jet structure and evolution. The method used to reveal this emergent underlying dynamics within jet turbulence, Stochastic Structural Stability Theory, will be described and illustrated with examples.
A54A-08
Variations in the lower stratospheric polar temperature in winter and spring associated with eddy heat flux
The lower-stratospheric polar temperatures and the eddy heat fluxes in winter and spring for the past 50 years were investigated based on NCEP/NCAR, ERA40 reanalysis data and a GCM run. Characteristic features of polar temperature in both Arctic and Antarctic stratosphere are described. The monthly mean polar temperatures at 70 hPa in January, February and March are compared with the eddy heat fluxes at 70 hPa averaged for the preceding two months, respectively. The eddy heat flux is divided into its stationary and transient components. Year-to-year variations of the polar temperature at 70 hPa are correlated with those of the stationary eddy heat flux in both mid- winter and early spring. However, the decadal components of polar temperature and eddy heat flux show different patterns. Examining the stationary and transient eddy heat fluxes separately, we show that the polar temperature variation in January is correlated with the stationary eddy heat flux from November 15 to January 15, whereas polar temperature in March is correlated with the transient eddies from January 15 to March 15. The variance of the stationary and transient eddies are also investigated for decadal and year-to-year components during winter and spring.