Ozone and stratospheric height waves for opposite phases of the QBO

The stratospheric quasi-biennial oscillation (QBO) provides an important source of interannual variations in the Northern Hemisphere. O'sullivan and Salby (1990) related extra-tropical eddy transport with the phase of the tropical QBO. When the tropical wind is easterly, the zero wind line is shifted into the winter hemisphere. Enhanced wave activity in middle latitudes acts to weaken the polar vortex. When the tropical wind is in the westerly phase the situation reverses. Heights at 30 mb and ozone configurations are contrasted in this paper for these two QBO phases. When the winter vortex deforms due to the amplification of planetary waves 1 and 2, extends westward and equatorward, the complementary band of low vorticity air spirals in toward the pole from lower latitudes. Sometimes, these planetary waves break (Juckes and McIntyre, 1987) and an irreversible mixing of air takes place between high and mid-latitudes. Global ozone patterns, as obtained form satellite observations, appear to be affected by planetary wave breaking (Leovy et al. 1985). This mixing results on regions with uniform ozone and potential vorticity. In the Southern Hemisphere (SH), Newman and Randel (1988) using Total Ozone Mapping Spectrometer (TOMS) data and the NMC analyses have found strong spatial correlation between the October mean temperature in the lower stratosphere and total ozone for the 1979 through 1986 years. Recently Nogues-Paegle et al.(1992) analyzed SH ozone and height data from 1986 to 1989. They found that leading empirical orthogonal functions (EOFs) for both ozone and 50 mb heights exhibit zonal wave 1 and 2 and that the correlations between ozone and 50 mb principal components (PCs) are high. The results were found to be consistent with a linear planetary wave advecting a passive tracer. In this paper, the dominant patterns of variability for 30 mb NMC heights and TOMS total ozone are obtained for the winter to summer transition (January to May) in the Northern Hemisphere (NH) for the years 1987-1990

Sources of Variability of Evapotranspiration in California

The variability (1990–2002) of potential evapotranspiration estimates (ETo) and related meteorological variables from a set of stations from the California Irrigation Management System (CIMIS) is studied. Data from the National Climatic Data Center (NCDC) and from the Department of Energy from 1950 to 2001 were used to validate the results. The objective is to determine the characteristics of climatological ETo and to identify factors controlling its variability (including associated atmospheric circulations). Daily ETo anomalies are strongly correlated with net radiation (Rn) anomalies, relative humidity (RH), and cloud cover, and less with average daily temperature (Tavg). The highest intraseasonal variability of ETo daily anomalies occurs during the spring, mainly caused by anomalies below the high ETo seasonal values during cloudy days. A characteristic circulation pattern is associated with anomalies of ETo and its driving meteorological inputs, Rn, RH, and Tavg, at daily to seasonal time scales. This circulation pattern is dominated by 700-hPa geopotential height (Z700) anomalies over a region off the west coast of North America, approximately between 32° and 44° latitude, referred to as the California Pressure Anomaly (CPA). High cloudiness and lower than normal ETo are associated with the low-height (pressure) phase of the CPA pattern. Higher than normal ETo anomalies are associated with clear skies maintained through anomalously high Z700 anomalies offshore of the North American coast. Spring CPA, cloudiness, maximum temperature (Tmax), pan evaporation (Epan), and ETo conditions have not trended significantly or consistently during the second half of the twentieth century in California. Because it is not known how cloud cover and humidity will respond to climate change, the response of ETo in California to increased greenhouse-gas concentrations is essentially unknown; however, to retain the levels of ETo in the current climate, a decline of Rn by about 6% would be required to compensate for a warming of +3°C.California Department of Water Resources/[4600002292]//Estados UnidosCalifornia Energy Commission///Estados UnidosU.S. Department of Energy///Estados UnidosUniversidad de Costa Rica//UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Geofísicas (CIGEFI

Variability of the South American Low Level Jet (SALLJ) in Various Time and Spatial Scales

Variability of the structure and spatial extension of the SALLJ is studies using a combination of various data sets (global reanalyses, PACS-SONET observations, OLR) and the data generated during the SALLJEX field experiment during the austral summer of 2003. On the circulation characteristics, SALLJ composites during the warm season show the enhanced low-level meridional moisture transport coming from equatorialSouth America as well as an upper level wave train emanating from the West Pacific propagating towards South America. The intensification of the warm season SALLJ obeys to the establishment of an upper-level ridge over southern Brazil and a trough over most of Argentina. The circulation anomalies at upper and lower levels suggest that the intensification of the SALLJ would lead to an intensification of the South Atlantic Convergence Zone SACZ later on, and to a penetration of cold fronts with an area of enhanced convection ahead at the exit region of the SALLJ. Regarding the time variability, SALLJ seems to occur all year long, with the SALLJs bringing tropical moist air masses from the Amazon into southern Brazil-Northern Argentina more frequent in the warm season, and the SALLJs bringing tropical maritime air less humid than the tropical air masses coming from the Subtropical Atlantic High more frequent during the cold season. SALLJs are detected mostly during the warm season to the North of 20S, while to the south the SALLJs seem to occur all year long. The diurnal cycle shows that SALLJs are more frequent and intense between 06 and 12 Z for the warm season north of 20 S, while at the region downstream the maximum is detected between 00 and 06 Z. during the cold season. At interannual time scales, even though there is a weak tendency for stronger and more frequent warm season SALLJ episodes in years with anomalously warm surface waters in the tropical Pacific, we cannot affirm with large degree of certainty that there is a strong relationship between the occurrence of El Niño events and the number and/or intensity of SALLJ episodes. However, the El Nino 1998 featured more frequent and intense warm season jet episodes than during La Nina 1999, and this has been demonstrated by the reanalyses, the available PACS-SONET upper-air observations and by other studies using independent data sets and regional modeling. RESUMO: O ciclo diurno do SALLJ mostra que o jato é mais forte e frequente entre as 0600 e 1200 Z durante o verão em latitudes ao norte de 20 °S, enquanto que na região de saída do jato o máximo é observado entre as 0000 e 0600 Z durante a estação de inverno. A variabilidade intrasazonal mostra associações entre a presença da SACZ, o SALLJ e a modulação de eventos extremos de chuva na região sudeste do Brasil. Aparentemente, o SALLJ ocorre durante todo o ano, mais os jatos trazendo umidade da Amazônia para o sul do Brasil são mais intensos no verão, e os jatos trazendo ar marítimo menos úmido (não tropical) do anticiclone do Atlântico Sul sub-tropical são mais frequentes no inverno. Na escala de tempo inter-anual, ainda que exista uma tendência de existir mais episódios de jatos em anos com temperaturas do Pacífico equatorial tropical, não existe uma evidência forte que indique com um alto grau de certeza que existe uma forte associação entre o número e intensidade de eventos jatos e a ocorrência do El Nino. Em escalas de tempo mais longas, existe uma tendência de ter mais episódios de jatos desde meados da década de 1970 s, consistente com tendências negativas de chuva no sul da Amazônia e no sul do Brasil-Norte da Argentina