Multiscale Interactions of climate variability and rainfall in the Sogamoso River Basin: Implications for the 1998–2000 and 2010–2012 multiyear La Niña events

In this research, we explored rainfall variability in the Sogamoso River Basin (SRB), its relationship with multiple scales of variability associated with El Niño–Southern Oscillation (ENSO), and the implications for rainfall prolongation during multiyear La Niña events. First, we examined time-frequency rainfall variations in the SRB based on the standardized precipitation index (SPI) from 1982 to 2019, using wavelet transform and principal component analysis (PCA). In addition, we applied wavelet analysis to investigate the links at different time scales between ENSO and the main mode of rainfall variability in the SRB. Finally, we explored the role that each scale of variability played in the prolongation and intensity of rainfall in the SRB during the 1998–2000 and 2010–2012 multiyear La Niña events. The results of the wavelet analyses revealed significant ENSO relationships affecting SRB rainfall at three different scales: quasi-biennial (2–3-years) between 1994 and 2002, as well as from 2008 to 2015; interannual (5–7 years) from 1995 to 2011; and quasidecadal (9–12 years) from 1994 to 2012. This indicates that multiyear events are a consequence of the interaction of several scales of variability rather than a unique scale. During the 1998–2000 event, El Niño conditions were observed during the first half of 1998; subsequently, a cooling of the central and eastern tropical Pacific (western tropical Pacific) on the quasi-biennial (interannual) scale was observed during 1999; in 2000, only La Niña conditions were observed on the interannual scale. Therefore, during this event, the quasi-biennial (interannual) scale promoted wet conditions in the Caribbean, the Andes, and the Colombian Pacific from June–August (JJA) 1998 to JJA 1999 (during 1999–2000). During the 2010–2012 La Niña event, the interbasin sea surface temperature gradient between the tropical Pacific and tropical North Atlantic contributed to strengthening (weakening) of the Choco jet (Caribbean low-level jet) on the quasi-biennial scale during 2010, and the interannual scale prolonged its intensification (weakening) during 2011–2012, acting to extend the rainy periods over most of the Colombian territory. Variations on quasi-decadal scales were modulated by the Pacific decadal oscillation (PDO), resulting in a further intensification of the 2010–2012 La Niña event, which developed under conditions of the cold PDO (CPDO) phase, whereas the 1998–2000 La Niña occurred during the transition from warm (WPDO, 1977–1998) to cold (CPDO, 2001–2015) conditions. These results indicate that the interaction of quasi-biennial to quasi-decadal scales of variability could play a differential role in the configuration and prolongation of rainfall events in the SRB

Principal modes of the total ozone on the Southern Oscillation timescale and related temperature variations

Total ozone and associated temperature variations on the Southern Oscillation timescale have been investigated using monthly total ozone mapping spectrometer and temperature data for the latitudinal domain between 70 degrees N and 70 degrees S and from 1979 to 1991. The first two modes for total ozone describe the anomalous total ozone patterns associated with the extremes in the Southern Oscillation. The first mode has the largest loadings in the southern hemisphere (SH) subtropics and midlatitudes with an east-west dipole in antiphase with a tropical east-west dipole. The second mode has its largest loadings in the tropics with an east-west dipolar pattern. These modes are intimately related to variations in the mean temperature in the lower stratosphere, and this relation is such that the total ozone and mean temperature anomalies are positively correlated. The tropospheric temperature patterns are confined in the tropics, where temperature and total ozone anomalies are negatively correlated. The tropical temperature and total ozone variations are driven by modulations in the tropical convection associated with the Southern Oscillation. The Southern Oscillation signals in the stratospheric temperature and in the total ozone are strongest in the SH midlatitudes during the winter-spring period and precede the extremes in the Southern Oscillation Index (SOI) by a few months. Thus the total ozone index, defined similarly to the SOI, seems to be more appropriate than the SOI to monitor the stratospheric temperature in the extratropics, in particular in the SH middle to high latitudes.Pages: 25797-2580

Does the El Niño-Southern Oscillation Affect the Combined Impact of the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation on the Precipitation and Surface Air Temperature Variability over South America?

Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) have combined effects on the precipitation (PRP) variability over South America. The combined impacts have been assessed considering four mean states as the averages of the variable anomalies during sub-periods overlapping time intervals of the PDO and AMO phases. Since these sub-periods include years under El Niño-Southern Oscillation (ENSO) extremes, the extent to which these years’ occurrence affects the averaged anomaly patterns during different mean states is investigated. The analyses are done for the PRP and surface air temperature (SAT) during the austral winter (June to August) and summer (December to February) of the 1901–2014 period using a composite technique. The nonlinear ENSO response in each mean state for a variable corresponds to the sum of the anomaly composites of the El Niño and La Niña events. In each mean state, the nonlinear PRP and SAT anomalies are not negligible and show similar patterns of the corresponding mean state, with larger magnitudes. For both seasons and all mean states, these similarities are more pronounced for SAT than for PRP. Thus, the ENSO variability affects the mean state’s PRP and SAT anomaly patterns in different ways. As far as we know, analyses of the nonlinear ENSO response of the South American climate during distinct mean states were not performed before. Our results also indicate that the ENSO variability should be considered in the studies of the low-frequency modes and their effects on the mean state over South America. The results presented could be relevant for climate monitoring and modeling studies

Intraseasonal (30-60 day) variability in the global tropics: principal modes and their evolution

The evolution of the 30-60 day intraseasonal (Madden-Julian) oscillation (MJO), during boreal winter and summer, is studied by means of extended empirical orthogonal function analyses. For both seasons, the patterns describe an eastward traveling large-scale oscillatory regime with a period of approximately 45 days. Several atmospheric variables display a zonal wavenumber one pattern approximately symmetric about the equator. The seasonal variation of the MJO is investigated, especially in terms of the intraseasonal variability of the tropical convection. We find that the latitudinal location of the largest outgoing longwave radiation anomalies is directly related to the seasonal meridional shifts of the tropical convection in the Indo-Australian and Central American-South American regions. In the eastern hemisphere, the MJO affects the monsoons over India during boreal summer and over Australia during austral summer. In the western hemisphere the MJO has the greatest impact on convection over Northeast Brazil during austral summer and over Central America during boreal summer. The MJO-related evolution of 925-hPa specific humidity patterns (not previously documented) show remarkable seasonal dependence. The boreal summer patterns contain a large-scale component quite similar to that shown in the sea level pressure patterns. The austral summer patterns show strong regional variability that might indicate the interactions of the MJO with deep tropical convection in certain areas, such as along the South Pacific Convergence Zone and over northern South America.Pages: 373-38

Zonally symmetric and asymmetric features of the tropospheric Madden-Julian oscillation

The evolving intraseasonal (IS) modes of the zonally symmetric (ZS) part (the latitudinal profile) of the 200-hPa stream function have been determined by performing extended empirical orthogonal function (EEOF) analyses for the northern hemisphere (NH) summer and winter. In each analysis the first EEOF mode describes an oscillation with a period of about 50 days. The prominent feature of the upper tropospheric stream function latitudinal profiles, for both seasons, is the propagation of the largest loadings in both hemispheres from near the equator toward higher latitudes. This propagation is more evident during the NH winter and throughout the year in the southern hemisphere (SH). In the NH the poleward propagation of the loadings is more conspicuous within the equator and the 30 degrees N latitudinal band. The associated patterns for the zonally asymmetric (ZA) part of the sea level pressure and the 850- and 200-hPa zonal winds have also been determined. These patterns feature, in general, the largest correlations in the tropics and a large-scale zonal wavenumber one structure propagating continuously eastward around the globe with a 50-day period. The ZA patterns for certain variables show strong seasonal dependence. The 850-hPa ZA zonal wind patterns feature the largest correlations approximately along the climatological position of the Intertropical Convergence Zone, whereas the largest correlations for the upper level ZA zonal wind patterns are found near the equator, mainly in the winter hemisphere.Pages: 13703-1371

A comparison of global tropospheric teleconnections using observed satellite and general circulation model total ozone column data for 1979-91

The total ozone column is well correlated with tropospheric fields such as the heights of the upper tropospheric geopotential surfaces and thus it can provide useful information on temporal variability in the troposphere. The global availability of long period satellite measurements of the total ozone column, taken by the TOMS instruments since 1978, provides a valuable and independent data set for use in studies of seasonal and interannual climate variability. In this study, the global low-frequency seasonal teleconnections in the observed TOMS data from 1979-91 have been investigated using seasonal teleconnectivity maps and empirical orthogonal function analysis. They have also been compared with the results from a simulation made with the atmospheric GCM at Meteo-France, having prescribed observed sea surface temperatures for the same period. In the observed total ozone, strong ENSO-related wave number one longitudinal dipole patterns are seen in both the tropics and in the Southern Hemisphere extratropics. The model shows much weaker variability in total ozone yet appears to be able to capture similar teleconnection patterns in the tropics related to ENSO. In the SH extratropics, the model total ozone shows a strong wave number 3 response rather than the wave number one dipole seen in the observations. A wave number 3 response is also evident in the 200 hPa geopotential height simulated by the model and in the NCEP analysis, and is consistent with the response in a linearised barotropic model forced in the Indonesian region. The different responses in the modelled and observed total ozone, suggest that tropopause effect is not the major factor in the SH extratropics, and it is likely that horizontal ozone transport also plays a role in this region. Despite a generally poor simulation of the zonal mean total ozone, the model was able to capture the anomalous strengthening of the SH stationary waves during austral spring of 1988, related to an intense stratosphere sudden warming.Pages: 133-15

High-frequency patterns of the atmospheric circulation over the Southern Hemisphere and South America

Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed data obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to March) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990-1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in selected areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the western hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15 degrees N and 70 degrees S are discussed. The high-frequency winter and summer patterns for both variables feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the southeastern Pacific. Analysis of the western hemisphere data reveal that the wavetrain in the South American sector extends northeastward over the continent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequential instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.Pages: 179-19

Summer circulation patterns related to the upper tropospheric vortices over the tropical South Atlantic

Daily 200-hPa relative vorticity data have been used to study the dominant patterns related to the cyclonic vortices over the South Atlantic Ocean in the vicinities of northeast Brazil, during the 1980-1989 period. Reference modes were obtained through empirical orthogonal function (EOF) analysis of the 200-hPa filtered vorticity anomalies over northeast Brazil, considering all the southern hemisphere (SH) summers within the study period. The amplitude time series of the first reference mode, separately for each SH summer, was correlated with the corresponding filtered vorticity anomalies in a larger area extending from 20 degrees N to 40 degrees S and between 120 degrees W and 20 degrees W. The correlation patterns feature a wave-like structure along eastern South America, with three main centers: the first one, over the South Atlantic off the northeast Brazil coast, is associated with the cyclonic vortices; the second one, over eastern Brazil, represents the corresponding anomalously amplified ridges; and the third one, over southern Brazil/Uruguay, is related to the equatorward incursions of midlatitude upper level troughs. This wave-like pattern is consistent with the vortex formation mechanism suggested in previous works. Another wave-like pattern southwest-northeast oriented is evident over the tropical southeastern Pacific, for some years. The interannual variability of these patterns is discussed in this paper.Pages: 203-21