Simple climatic indices for the tropical Atlantic Ocean and some applications

“This polar behaviour across the ITCZ also can be observed by applying PCA to the Atlantic SSTA field, which is used as the basis of a dipole index (Weare, 1977; Hastenrath, 1978; Servain, 1991).”

“…indices such as: ‘NINO3’ in the equatorial Pacific Ocean (150◦W–90◦W and 3◦S–3◦N, from OGP/NOAA), ‘ATL3’ in the equatorial Atlantic Ocean (20◦W-GMT and 3◦S–3◦N, following Servain 1991), and the PSA 500 hPa geopotential index as defined by Mo (2000), and re-analyzed by Robertson and Mechoso (2003).”

“The correlations of the AWP with the tropical Atlantic meridional gradient mode (AMM) (Servain 1991; Chang et al. 1997, Xie et al. 1999; Enfield et al. 1999; Xie and Carton 2004) and theAtlantic Ni~no (Zebiak 1993; Carton and Huang 1994; Latif and Gr€otzner 2000; Okumura and Xie 2006) are statistically significant but…”

“Positive (negative) GRAD index denotes the northward (southward) SST gradient over the intertropical Atlantic basin (Servain 1991; De Souza et al.”

“Nevertheless, the index formed by the SST anomaly difference between the tropical North Atlantic and tropical South Atlantic (Servain, 1991), sometimes referred to as a dipole index, has proved to be an invaluable indicator of the meridional gradient in SST anomaly that is correlated with strong…”

“Servain (1991) introduced the AZM as the equatorial sea surface temperature (SST) anomaly and defined the AMM as the anomalous inter-hemispheric SST gradient with negative AMM corresponding to a negative/positive SST anomaly in the Northern/Southern Hemisphere.”

“…Atlantic (0°–20°S) SSTA regions to correlate antisymmetrical across the ITCZ in what is sometimes referred to as the tropical Atlantic dipole (Weare 1 Servain 1991), and for such covariability to be strongly related to rainfall anomalies in North Africa and Northeast Brazil (e.g., Moura and…”

“Another important issue concerning the NTAM is the linkage with the Southern Tropical Atlantic Mode (STAM), as part of the tropical meridional mode (Servain 1991).”

“In fact, the role of the SSTs on the ITCZ variations has been already reported by several authors (Moura and Shukla, 1981; Nobre and Shukla, 1996; Servain, 1991; Chang et al., 2000).”

“, 1997) and dipole (Servain, 1991; Huang and Shukla, 1997) modes of low-frequency variabilities observed in this oceanic region.”

“Numerous studies have shown that sea-surface temperatures (SST), both on global and regional (Atlantic ocean) scales, play a major part in the interannual variability of West African rainfall (Lamb, 1978; Hastenrath, 1984; Lough, 1986; Folland et al., 1986; Wolter, 1989; Servain 1991; Janicot, 1992b; Ward, 1992; Fonta…”

“…and the tropical Atlantic meridional mode SST index (SST anomaly difference between 58 and 258N, 558 and 158W and between 08 and 208S, 308W and 108E) (Servain 1991; Wang 2002). b. Analysis domains We focus mainly on precipitation variability in the Atlantic marine ITCZ (AMI), which has a strong…”

“1999; Mo and Häkkinen 2001), and longer interannual time scales have been associated with northern Atlantic (Servain 1991; Tourre et al. 1999; Rajagopalan et al. 1998; Mo and Häkkinen 2001).”

“This definition is similar to that used by Servain (1991) (SST averaged over 58–288N, 608W–158E minus 208S–58N, 608W–158E), although we place a slightly stronger emphasis on lower latitudes, which are likely to affect atmospheric circulation and rainfall most strongly.”

“Some authors used the TA basins north and south of the thermal equator, 5 N, as the TNA and TSA representative areas (Servain, 1991; Melice and Servain, 2003; Huang et al., 2005).”

“Outros pesquisadores também destacam a relação entre a precipitação e o Atlântico Tropical em estudos observacionais e estatísticos, como as realizadas por Hastenrath e Heller (1977), e também com simulações numéricas por Moura e Shukla (1981), Servain (1991), Nobre e Shukla (1996).”

“There is evidence of decadal variability in the tropical Atlantic, which is believed to have important climate impacts (Moura and Shukla 1981; Servain 1991 ).”

“Anomalias positivas de TSM no Atlântico Tropical sul produzem precipitação sobre o leste do NEB, enquanto anomalias positivas de TSM no Pacífico inibem a chuva no Leste do NEB. 3.”

“The indices used, represent signatures of climate signals and SST variability in various part of the tropical oceans such as: ‘‘NINO3’’ in the equatorial Pacific ocean (150W–90W and 3S–3N, from OGP/NOAA), ‘‘ATL3’’ in the equatorial Atlantic ocean (20W–GMT and 3S–3N, following Servain [1991] ), and ‘‘IO1’’ in the equat…”

“In addition, Atlantic SST anomalies have been linked to precipitation anomalies in northeastern SA (e.g., Hastenrath & Heller, 1977; Nobre & Shukla, 1996; Servain, 1991), where positive (negative) equatorial Atlantic SST anomalies are correlated to abundant (deficient) rainfall.”

“Two El Niño-like phenomena in the South Atlantic, namely Atlantic Niños and Benguela Niños, have also been identified (Servain 1991; Ruiz-Barradas et al. 2000).”

“Our study indicates that this Atlantic SST dipole mode (DM) [Servain, 1991] could have played an important role in creating Florida’s 2004 hurricane havoc.”

“For the Atlantic Ocean the observed SST of the north (28‡N– 5‡N; 60‡W–Africa) and south (5‡N–20‡ S; America–Africa) basins are from the monthly standardized SST anomalies dataset (1964–1999) provided by Servain (1991).”

“[28] Similar to Servain et al. [1999], we examined the relation between these modes and interannual ITCZ position anomalies (here based on a zero-wind stress-curl criterion), finding a good correlation between the meridional mode and”

“2), which leads us to somewhat smaller spatial regions than used by Servain (1991).”

“…waves play a significant role in the generation of SST anomalies and coherent atmospheric responses and impacts (Nicholson and Entekhabi, 1987; Servain, 1991; Zebiak, 1993; D’Abreton and Lindesay, 1993; Curtis and Hastenrath, 1995; Mehta and Delworth, 1995; * To whom all correspondence should…”

“2a–d, f–i) in the equatorial Atlantic is similar to the Atlantic Meridional Mode (AMM) a non-ENSO coupled ocean/atmosphere variability in the Atlantic basin (Servain 1991), of which has been found to be forced by the NAO (Chiang and Vimont 2004).”

“This mode has been claimed to be one of the main features of the decadal variability in the tropical Atlantic (e.g., Servain, 1991; Andreoli and Kayano, 2003).”

“Observational studies that focused on SST alone tended to reproduce the ‘‘dipole’’ structure (Servain 1991) formed by the northern and southern tropical Atlantic SST anomalies on multidecadal time scales, but emphasized the lack of interhemispheric coherence between the two centers of action on…”

“In the tropical Atlantic, for example, the interhemispheric sea surface temperature (SST) gradient and the cross-equatorial surface wind display significant coherence on interannual– decadal time scales (Servain 1991; Nobre and Shukla 1996; Chang et al. 1997), which is known as the Atlantic meridional mode, causing st…”

“It was originally identified by Servain [67].”

“Another mode of variability is the so-called zonal mode or Atlantic Nin˜o and is predominant in the boreal summer (Servain 1991; Tokinaga and Xie 2011; Carton and Huang 1994; Zebiak 1993; Shannon et al. 1986).”

“At interannual time scales, two main modes emerge from observational studies: the meridional or dipole mode (Weare 1977; Servain 1991; Nobre and Shukla 1996; Corresponding author address: Serena Illig, LEGOS, 14 av. E. Belin, 31400 Toulouse, France.”

“O modo de dipolo envolve variações de TSM em ambos os hemisférios, em escalas de tempo sazonal, interanual e decenal (Servain, 1991).”

“Also, the ENSO-independent NATL variability is also possibly linked to the dipole mode reported in Moura and Shukla (1981), Servain and Legler (1986), and Servain (1991).”

“Hence, there is a spuriously strong interaction between the zonal and AMM mode.”

“Then, SST anomalies are averaged for boreal winter and filtered through a decadal band of 8–16 year, a frequency domain that contains large SST variance (Servain 1991; Mehta 1998; Rajagopalan et al. 1998; Tourre et al. 1999).”

“…a dipole pattern in precipitation and an anomalous interhemispheric SST gradient, is believed to be a coupled mode intrinsic to the tropical Atlantic (Servain 1991; Mehta and Delworth 1995; Nobre and Shukla 1996; Tourre et al. 1999; Servain et al. 2000; Sutton et al. 2000; Chang et al. 2000, 2001).”

“…the difference between the area-averaged SSTA (with ENSO influence removed) in north equatorial Atlantic (NEA, 0.5◦ N–20.5◦ N, 84.5◦ W–16.5◦ E) and south equatorial Atlantic (SEA, 0.5◦ S–20.5◦ S, 84.5◦ W–16.5◦ E), which is widely adopted in previous studies (Servain 1991, Melice and Servain 2003).”

“Autores associam-a ao ciclo de manchas solares e ao Dipolo do Atlântico (Servain, 1991; Kerr, 1996; Clauzet e Wainer, 1999; Echer, 2003; Molion, 2005).”

“intertropical convergence zone (ITCZ) [Moura and Shukla, 1981; Servain, 1991].”

“of sea surface temperature (SST) in the tropical Atlantic, which is associated with the anomalous latitudinal displacement of the ITCZ [5,7,8,13] between February and May.”

“Such LHF and PWS patterns agree quite well with the positive impact of the meridional SST gradient on the rainfall variability in the NNEB [4] [5], which has already been widely discussed in the literature (cold SST in the North, warm SST in the South) and is fully illustrated in Figure 4 of Hounsou-Gbo et al.”

“On the other hand, NTA is closely linked to the Atlantic meridional mode (Chiang and Vimont 2004) and/or the dipole mode (Servain 1991), which emphasize the anomalous fluctuation of the cross-equatorial SST gradient.”

“The fifth plot is for the tropical Atlantic basin (data from SERVAIN, 1991).”

“For example, the studies of (Moura and Shukla 1981; Servain 1991; Wainer and Soares 1997; Hastenrath 2012) among others, all related changes in Tropical SST with the migration of the Intertropical Convergence Zone (ITCZ) and rainfall in Brazil, particularly in its Northeast region (NEB).”

“0 index (3◦ S–3◦ N, 20◦ W–0◦, Zebiak, 1993), and the TNA-TSA index (SST anomaly difference between 5◦–25◦ N, 55◦–15◦ W and 0◦–20◦ S, 30◦ W–10◦ E, Servain, 1991), were used in a multi-variable regression technique to remove their coherent signals in both aerosol and precipitation time series.”

“[2] With respect to sea surface temperature (SST), the tropical Atlantic ocean displays two dominant modes of interanual variability largely described in the literature [e.g. Servain, 1991; Wainer et al., 2002; Servain et al., 2002].”

“Using the SST and wind component indices given by Hastenrath (1990), Rao et al. (1993), Servain (1991) and Servain and Lukas (1990) for the Atlantic region and the NE Brazil coast, Kane (1999) showed that for some El Niño events shown in Table 2, the droughts did not occur because the Atlantic…”

“Rather, it displays two modes of variability: a decadal meridional sea surface temperature (SST) gradient mode coupled with cross-equatorial wind anomalies and an interannual zonal SST mode coupled with along-equatorial wind anomalies (e.g., Servain 1991; Tanimoto and Xie 1999).”

“…instance the meridional gradient in sea surface temperature (SST) linked to changes in trade winds (Covey & Hastenrath, 1978; Handoh et al., 2006; Servain, 1991; Zhang & Delworth, 2005) and the InterTropical Convergence Zone (ITCZ), a broad region of low atmospheric pressure, transporting water…”

“Por outro lado, os anos correspondentes aos anos com GRADM positivo ou negativo foram escolhidos com base no cálculo do índice proposto por Servain (1991), que consiste na diferença entre as médias da TSM na área delimitada na bacia norte do Atlântico por 60ºW-20ºW, 5ºN-28ºN, menos a área na bacia…”

“Nonetheless, the decadal signal is prominent be- tween the the years 1960–1990 (e.g. Servain, 1991).”

“The dipole index was originally proposed by Servain (1991), who defined the index based on SST anomalies in tropical regions of the Atlantic ocean.”

“This uncertainty is a result of the lack of quality of the coupled ocean-atmosphere models in representing the amplitude and frequency of ENSO events, and primarily in representing the Tropical Atlantic Sea Surface Temperature (SST) variability, once that their SST modes drive the annual rainfall anomalies in NNB (Ser…”

“Enfield and Mayer 1997, Fig. 5). Aside from any linkage with ENSO, we note that interpretation of tropical Atlantic SST in terms of a meridional dipole, as proposed by Servain (1991) , was recently reevaluated using alternative forms of spatial decomposition (see discussions in Enfield and Mayer 1997; Enfield et al. 1…”

“2000; Servain 1991).”

“As temperaturas nas áreas do Atlântico Tropical Norte (ATN) e Atlântico Tropical Sul (ATS) correspondem à região associada ao padrão de Dipolo do Atlântico Tropical (Moura & Shukla, 1981; Servain, 1991).”

“Positive and negative SST anomaly cores thus form an anomalous oceanic dipole, similar to the historical dipole studied many times in the past [35].”

“The other mode, first identified by Servain (1991) using principal component analysis, is characterized by an anomalous meridional SST gradient due to a north-south oscillation in SSTs.”

“Since the South Atlantic was cooler and the North Atlantic was warmer, the Atlantic SST dipole, coined by Servain [43], was positive for most of 2008.”

“The negative correlation of SSTs in the northwest and the southeast tropical Atlantic as a dipole across the ITCZ has been inferred from the results of the empirical orthogonal function (EOF) analysis and principal component analysis (Weare, 1977; Moura and Shukla, 1981; Servain, 1991).”