Air-sea interactions and dynamical processes associated with the midsummer drought

Herrera, E.; Magaña, Víctor; Caetano, Ernesto

doi:10.1002/joc.4077

Cited by 63 publications

(78 citation statements)

References 26 publications

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“…For example, from Fig. 4, one can see that in the southern part of Central America (Panama, Costa Rica, Nicaragua) the MSD tends to start, develop and end earlier than in the northern part (El Salvador, Guatemala, Honduras), in agreement with previous studies such as Alfaro (2002) and Herrera et al (2015). In the southern stations, typically, the start of the MSD is detected by 20 June, the minimum is reached by 19 July and the end by 20 August, meanwhile at the north the start is observed by 22 June, the minimum by 24 July and the end around 24 August.…”

Section: Advsupporting

confidence: 90%

“…This hypothesis, nevertheless, does not explain the almost simultaneous occurrence of the MSD in both southern Mexico and Central America (Magaña et al, 1999). On the other hand, Herrera et al (2015) describe the origins of the MSD studying the air-sea interaction between the CLLJ (Amador, 1998(Amador, , 2008Muñoz et al, 2008;Maldonado et al, 2016) and the ocean waters in the neighbourhood of the Pacific coast. Their findings show that the CLLJ peaks in July, provokes a cooling of the SSTs over the Pacific and a westward shift of low-level moisture convergence that combined with subsidence produce the MSD.…”

mentioning

confidence: 99%

“…Recent studies such as Karnauskas et al (2013) and Herrera et al (2015) have proposed different hypothesis about the origin of the MSD. Karnauskas et al (2013) argue that the MSD originates as a response to one single precipitation-enhancing mechanism occurring twice, contrary to a suppressing mechanism.…”

mentioning

confidence: 99%

“…Most of the population lives in the Central American Pacific slope. Although the MSD is present almost every year, it shows high variability in space and time (Amador, 2008;Alfaro, 2014), and the understanding of this variability is still a scientific challenge Amador, 2008;Herrera et al, 2015). The beginning, and duration are uncertainty factors for different socio-economic sectors such as the agricultural and potable water supply.…”

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confidence: 99%

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Interannual variability of the midsummer drought in Central America and the connection with sea surface temperatures

et al. 2016

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Abstract. The midsummer drought (MSD) in Central America is characterised in order to create annual indexes representing the timing of its phases (start, minimum and end), and other features relevant for MSD forecasting such as the intensity and the magnitude. The MSD intensity is defined as the minimum rainfall detected during the MSD, meanwhile the magnitude is the total precipitation divided by the total days between the start and end of the MSD. It is shown that the MSD extends along the Pacific coast, however, a similar MSD structure was detected also in two stations in the Caribbean side of Central America, located in Nicaragua. The MSD intensity and magnitude show a negative relationship with Niño 3.4 and a positive relationship with the Caribbean low-level jet (CLLJ) index, however for the Caribbean stations the results were not statistically significant, which is indicating that other processes might be modulating the precipitation during the MSD over the Caribbean coast. On the other hand, the temporal variables (start, minimum and end) show low and no significant correlations with the same indexes.The results from canonical correlation analysis (CCA) show good performance to study the MSD intensity and magnitude, however, for the temporal indexes the performance is not satisfactory due to the low skill to predict the MSD phases. Moreover, we find that CCA shows potential predictability of the MSD intensity and magnitude using sea surface temperatures (SST) with leading times of up to 3 months. Using CCA as diagnostic tool it is found that during June, an SST dipole pattern upon the neighbouring waters to Central America is the main variability mode controlling the inter-annual variability of the MSD features. However, there is also evidence that the regional waters are playing an important role in the annual modulation of the MSD features. The waters in the PDO vicinity might be also controlling the rainfall during the MSD, however, exerting an opposite effect at the north and south regions of Central America.

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Section: Advsupporting

confidence: 90%

mentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Interannual variability of the midsummer drought in Central America and the connection with sea surface temperatures

et al. 2016

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“…The MSD is a relative minimum in convective activity during July and August that coincides with an intensification of the Caribbean Low Level Jet (CLLJ) (mean flow at 925 hPa). Until now, it is not clear what the mechanism that maintains the CLLJ is, but it appears that the effect of the mean convergence of easterly momentum, by means of tropical extratropical interactions over the Caribbean Sea, plays an important role [2]. Cook and Vizy (2010) observed that an intense CLLJ is related to negative precipitation anomalies in summer over most of the IAS region [3].…”

Section: Introductionmentioning

confidence: 99%

Transient-mean flow interactions over the northern tropical Americas

Magaña

Herrera

2017

Proceedings of First International Electronic Conference on the Hydrological Cycle

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Abstract:The Mid Summer Drought (MSD) over the Mesoamerican region constitutes a unique feature of its precipitation seasonal cycle. The MSD is a relative minimum in convective activity during July and August that coincides with an intensification of the Caribbean Low Level Jet (CLLJ) (mean flow at 925 hPa). There is not a unique theory on what maintains the CLLJ is, but the effect of the mean meridional convergence of easterly momentum related to tropical extratropical interactions over the Caribbean Sea, appars to play an important role. The barotropicaly unstable nature of the CLLJ shows that when this mean circulation is intense the amplification of high frequency transients (eg, easterly waves) is inhibited. Empirical observational evidence shows that as the CLLJ intensifies above a certain magnitude, transient activity decreases. Such transient activity is related to easterly waves, a key element in producing precipitation over the tropical Americas. Therefore, the CLLJ acts as a modulator of tropical convection in relation to the MSD, as the period of relatively minor tropical convection coincides with a decrease in high frequency Perturbation Kinetic Energy (PKE). Its role in the modulation of convective activity over the tropical Americas on interannual and even on interdecadal time scales makes it one of the key elements to understand climate variability over the tropical Americas.

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The role of the meridional sea surface temperature gradient in controlling the Caribbean low‐level jet

et al. 2017

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The Caribbean low‐level jet (CLLJ) is an important modulator of regional climate, especially precipitation, in the Caribbean and Central America. Previous work has inferred, due to their semiannual cycle, an association between CLLJ strength and meridional sea surface temperature (SST) gradients in the Caribbean Sea, suggesting that the SST gradients may control the intensity and vertical shear of the CLLJ. In addition, both the horizontal and vertical structure of the jet have been related to topographic effects via interaction with the mountains in Northern South America (NSA), including funneling effects and changes in the meridional geopotential gradient. Here we test these hypotheses, using an atmospheric general circulation model to perform a set of sensitivity experiments to examine the impact of both SST gradients and topography on the CLLJ. In one sensitivity experiment, we remove the meridional SST gradient over the Caribbean Sea and in the other, we flatten the mountains over NSA. Our results show that the SST gradient and topography have little or no impact on the jet intensity, vertical, and horizontal wind shears, contrary to previous works. However, our findings do not discount a possible one‐way coupling between the SST and the wind over the Caribbean Sea through friction force. We also examined an alternative approach based on barotropic instability to understand the CLLJ intensity, vertical, and horizontal wind shears. Our results show that the current hypothesis about the CLLJ must be reviewed in order to fully understand the atmospheric dynamics governing the Caribbean region.

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Air-sea interactions and dynamical processes associated with the midsummer drought

Cited by 63 publications

References 26 publications

Interannual variability of the midsummer drought in Central America and the connection with sea surface temperatures

Interannual variability of the midsummer drought in Central America and the connection with sea surface temperatures

Transient-mean flow interactions over the northern tropical Americas

The role of the meridional sea surface temperature gradient in controlling the Caribbean low‐level jet

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