Pablo O. Canziani

Equatorial Kelvin wave variability during 1992 and 1993

Temperature and ozone data from the Microwave Limb Sounder (MLS) instrument on UARS are used to analyze the variability of Kelvin wave activity during the first two years of the UARS mission. The analysis is carried out using the asynoptic mapping technique. Time frequency plots for zonal wavenumbers 1 and 2, at two heights representing the middle stratosphere and the stratopause, respectively, are used to analyze the temporal variability of the waves, and its possible relationship to the equatorial quasi-biennial oscillation (QBO) and semiannual oscillation (SAO). Kelvin wave activity reaches a maximum during the solstice seasons and almost disappears during the equinoxes, in agreement with previous studies. Eastward propagating variance is estimated for wave periods from 4 to 20 days, at all UARS pressure surfaces currently available for MLS. The semiannual modulation of variance is observed to extend down to the lower limits of the height ranges of the temperature and ozone retrievals. Furthermore, a superposed QBO modulation is detected up to the stratopause. Comparison between the variance in eastward propagating waves and the mean zonal wind shows a possible participation of kelvin waves in the forcing of the QBO. At the stratopause the role of Kelvin waves in forcing the SAO appears to be limited, in agreement with previous results. Between the 21-hPa and 4.6-hPa surfaces there appears to be a transition zone where there is no clear relationship between Kelvin wave activity and mean zonal flow acceleration.

Kelvin waves and the quasi-biennial oscillation: An observational analysis

A method is derived for estimating the Kelvin wave contribution to the vertical flux of westerly momentum in the equatorial stratosphere, which is based on temperature and geopotential perturbations. This method is used to estimate the momentum transfer due to Kelvin wave activity as derived from the cryogenic limb array etalon spectrophotometer (CLAES) temperature data set, for the onset of the westerly phase of the QBO during 1992 and the first few months of 1993, that is, during the first part of the Upper Atmosphere Research Satellite (UARS) mission. The results are compared with the zonal winds as observed by the high-resolution Doppler imager (HRDI) also flown on board UARS, and the United Kingdom Meteorological Office (UKMO) data assimilation model product, a correlative data set to the UARS mission. The analysis shows that although the Kelvin wave momentum flux convergence is occasionally sufficient to account for the observed QBO westerly acceleration, the observed flux is sporadic in nature and virtually disappears during the second half of the sample, when the westerly vertical shear zone approaches the 100 hPa level. An estimate of the total westerly momentum flux necessary to produce the observed descent of the westerly phase of the QBO is made using the transformed Eulerian mean (TEM) formalism. The results suggest that Kelvin waves are not sufficient to force the descent of the westerly phase of the QBO. There appears to be a need for enhanced westerly forcing throughout the descent of the westerly phase of the QBO. This enhanced forcing is most likely provided by gravity waves that are unresolved by the satellite observations. These results are in agreement with the results derived from general circulation models.

Trends evolution of ozone between 1980 and 2000 at midlatitudes over the Southern Hemisphere: Decadal differences in trends

[1] The variability of atmospheric midlatitudinal ozone between 1980 and 2000 over the Southern Hemisphere is discussed. The distribution of ozone and ozone change during the seasonal cycle is discussed using Total Ozone Mapping Spectrometer Nimbus and Earth Probe data binned at 72 (30� longitude by 5� latitude) bins, between 60� and 30� S. Rather than using a standard trend approach, the annual mean time series for each bin were fitted with a cubic polynomial. The results show that in the zonal mean sense there is a sizable, latitude-dependent slowdown of the ozone loss from the early 1990s onward, but when individual bins are considered, significant longitudinal patterns of ozone change appear, with both positive (enhancement) and negative (depletion) changes in total ozone. Thus regional evolution remains important as an indicator both of chemical depletion evolution and the relation with climate. Such longitudinal behavior is limited in the subtropics and grows toward the subpolar edge of the sampled region. For example, a large decrease was observed over southern South America in the 1980s, but during the 1990s there was only a limited change. The analysis for January, June, and October over the 20-year period shows changes in the evolution along the year, both in time and space. Furthermore, such seasonally dependent changes reach a peak in October, as would be expected. The October pattern of interannual variability could be linked to Southern Annular Mode, though there probably are some other processes driving it.

On tidal variability and the existence of planetary wave-like oscillations in the upper thermosphere—I. Observations of tidal variability

Abstract The evidence for the existence of tidal variability as observed in the meridional thermospheric wind (approx. 300 km height) is presented for a set of eight ionosonde locations (three in the northern hemisphere and five in the southern hemisphere). The data set corresponds to a full year (1984) of hourly values. The detected variability can be seen in the tidal components of the meridional wind. The diurnal and semidiurnal components are spectrally analysed. The quarterly spectra show that the tidal amplitudes oscillate with periods between 2 and 60 days. The more important oscillations have periods from 15 to 3 days. No direct link between solar and magnetic activity indices was detected. Possible reasons for the observed tidal variability are discussed in the light of the current theory developed for the mesosphere and lower thermosphere.

On tidal variability and the existence of planetary wave-like oscillations in the upper thermosphere. II: Non-linear interactions and global scale oscillations

Abstract In Part 1 of this paper the variability of diurnal and semidiurnal components of the meridional thermospheric wind was discussed. The observed variability is discussed in the light of the non-linear theory of wave-wave interactions. It is shown that it is possible to explain, at least partially, the variability through the non-linear interactions of tides with long period oscillations having periods between 2 and 15 days. Given that the periods obtained both from the quarterly spectra of the tidal amplitudes and the non-linear interaction analysis coincide with periods reported in the literature for planetary waves in the lower and middle atmosphere, the existence of global scale oscillations are sought in the upper atmosphere. Wave events are observed, coincident with the above-mentioned periods, for a set of five longitudinally distributed locations between 30 and 35 S throughout the yearly samples. The wave events have basically westward phase displacements though eastward travelling phases are observed at times.

Regional Climate Variability Impacts on the Annual Grape Yield in Mendoza, Argentina

AbstractMendoza Province is the major Argentinian vitivinicultural region, and its grape production is fundamental for the national vintage. The 1979–2009 climate–annual grape yield relationships are analyzed, and total grape yield is shown to depend significantly on regional “summer” (October–March) precipitation. Precipitation negatively affects yields through plant disease and damage/destruction by hail. At interannual scales, summer regional precipitation variability can explains 25% of the yield variance. Summer precipitation modulates yield with a 6–8-yr period: wet (dry) summers can be associated with larger (smaller) grape damage/loss probability during the summer preceding the vintage, as well as lower (higher) grape yields in the subsequent annual campaign because of bud damage. With respect to monthly mean precipitation at Mendoza Observatory, wetter Novembers/Decembers can lead to lower yields. Hail during the summer of the previous harvest and during December could lower yields. Winter, late ...

Ozone and upper troposphere/lower stratosphere variability and change at southern midlatitudes 1980–2000: Decadal variations

[1] Total ozone relationships with selected upper troposphere/lower stratosphere variables (400- and 70-hPa temperatures, tropopause height and temperature, 70-hPa geopotential height, and 340-K potential vorticity), as well as between the variables, are analyzed on decadal scales over Southern Hemisphere midlatitudes for the period 1980-2000. Total Ozone Mapping Spectrometer version 8 total ozone and European Centre for Medium Range Weather Forecast ERA-40 data products for June and October (early winter and spring) are used. Multiple spatial correlation techniques and shared variance estimates are applied to infer relationships between mean fields as well as among decadal difference fields. Wave activity Z and local Eliassen-Palm fluxes were calculated to further analyze the dynamics of the samples and their variability. The statistical studies show that observed total ozone latitudinal and longitudinal decadal variations can be driven by upper tropospheric and stratospheric variability, depending on latitude and season. The sampled regions, divided into subtropical and subpolar, yield differentiated relationships. October ozone decadal variations during the 1980s, particularly at higher latitudes, are attributed primarily to chemical ozone depletion, while there appear to be links between tropospheric decadal change and some of the stratospheric variables and tropopause behavior. In the 1990s, tropospheric contributions decrease, and stratospheric quasi stationary wave 1 plays a major role. In June, tropospheric change/variability appears to be more important than stratospheric driving, which nevertheless also contributes to change. Ozone change in the 1990s responded more to stratospheric dynamic change at higher latitudes, but despite reduced contributions, the troposphere remains a driver of variation at the lower latitudes of the sample.

Linear and Non-Linear Trends for Seasonal NO2 and SO2 Concentrations in the Southern Hemisphere (2004−2016)

In order to address the behaviour of nitrogen dioxide (NO2) and sulphur dioxide (SO2) in the context of a changing climate, linear and non-linear trends for the concentrations of these two trace gases were estimated over their seasonal standardised variables in the Southern Hemisphere—between the Equator and 60° S—using data retrieved by the Ozone Monitoring Instrument, for the period 2004–2016. A rescaling was applied to the calculated linear trends so that they are expressed in Dobson units (DU) per decade. Separately, the existence of monotonic—not necessarily linear—trends was addressed by means of the Mann-Kendall test. Results indicate that the SO2 exhibits significant linear trends in the planetary boundary layer only; they are present in all the analysed seasons but just in a small number of grid cells that are generally located over the landmasses or close to them. The SO2 concentrations in the quarterly time series exhibit, on average, a linear trend that is just below 0.08 DU decade−1 when significant and not significant values are considered altogether, but this figure increases to 0.80 DU decade−1 when only the significant trends are included. On the other hand, an important number of pixels in the lower troposphere, the middle troposphere, and the lower stratosphere have significant monotonic upward or downward trends. As for the NO2, no significant linear trends were found either in the troposphere or in the stratosphere, yet monotonic upward and downward trends were observed in the former and latter layers, respectively. Unlike the linear trends, semi-linear and non-linear trends were seen over the continents and in remote regions over the oceans. This suggests that pollutants are transported away from their sources by large-scale circulation and redistributed hemispherically. The combination of regional meteorological phenomena with atmospheric chemistry was raised as a possible explanation for the observed trends. If extrapolated, these trends are in an overall contradiction with the projected emissions of both gases for the current century.

Annual anomalies and trends for TOMS reflectivities 1978–2005 in the Southern Hemisphere

ABSTRACT Annual anomalies of Lambertian equivalent reflectivity (LER) retrieved from the total ozone mapping spectrometer spanning the period November 1978–November 2005 were studied in the Southern Hemisphere, in a region bounded by 0° S and 60° S, and their trends were estimated. With the exception of few regions where the variable may represent the contribution of both cloudiness and snow, trends in LER anomalies provided an evolution of total cloudiness. On average, the study region experienced a net increase in LER values of 0.78 reflectivity units (RU) decade−1; if only significant trend values are considered this figure increased to 1.18 RU decade−1. The region that showed the largest upward trend, up to 4 RU decade−1, was located over the eastern Pacific, off the coasts of Chile and Peru, where the presence of marine stratocumulus is frequent. Despite the overall positive trend there were regions that yielded a negative one, most notably the tropical latitudes of South America and Africa. The yearly zonal means also showed a positive trend at all latitudes, but significance occurred beyond 20° S only. Correlation maps between LER anomalies and five different circulation indices were also introduced. The indices with the highest and lowest number of significant correlation values were the Madden–Julian oscillation at 70° E and the quasi-biennial Oscillation, respectively.

A seasonal climatology of UV reflectivity for southern South America

ABSTRACT A seasonal climatology for the Lambertian equivalent reflectivity (LER) in ultraviolet (UV) for southern South America is introduced. The study region was limited by 10° and 60°S and by 100° and 30°W; the data set spanned the period 1978–2015. Features of the seasonal means and of the quarterly (Q) and the interannual (IA) variabilities for each season were ascribed to atmospheric and oceanic processes of local, regional, or global origin which lead to the formation or maintenance of clouds. Shifts in the Q and IA time series were detected, most notably in the early 1990s. Linear trends were also estimated. The largest positive and negative trends in the Q time series were found along the Peruvian Andes (PA) (3.20 reflectivity units [RU] decade−1) and east of the Chapada Diamantina (CD) and the Serra do Espinhaço (SE) in Brazil (−1.40 RU decade−1), respectively. The largest positive and negative trends in the IA time series were found in PA (6 RU decade−1, summer) and east of CD and SE (−2.50 RU decade−1, spring), respectively. The linkages between UV LER and regional or global circulation indices were also studied. The largest relationships were found with the Dipole Mode Index on a Q basis and with the Southern Oscillation Index on an IA basis in winter.