The Spatial Pattern of Midsummer Drought as a Possible Mechanistic Response to Lower-Tropospheric Easterlies over the Intra-Americas Seas

Zermeño‐Díaz, David Maximiliano

doi:10.1175/jcli-d-18-0528.1

Cited by 5 publications

(7 citation statements)

References 43 publications

(51 reference statements)

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“…The WT method proved useful to separate the wet season in each dataset into three stages: the first and second peak periods (P1 and P2) and the drier period (MSD). This approach was able to reproduce the so-called "MSD patterns" reported in previous studies (Zermeño-Díaz, 2019, Zhao et al, 2020 using various diagnostics such as OLR, ω and the low-level winds.…”

Section: The Role Of the Caribbean Low-level Jetmentioning

confidence: 80%

“…The third hypothesis argues that the MSD is related to the CLLJ variability (Herrera et al, 2015, Zermeño-Díaz, 2019, Martinez et al, 2019. Synchronous changes to the zonal wind, the integrated moisture flux convergence (IMFC) and the precipitable water vapor suggest that the low-level wind flow in the Caribbean varies coherently with the stages of the MSD.…”

Section: The Role Of the Caribbean Low-level Jetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Revisiting mechanisms of the Mesoamerican Midsummer drought

García‐Franco

Chadwick

Gray

et al. 2022

Preprint

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Observations show that the seasonal cycle of precipitation in parts of southern Mexico and Central America exhibits a bimodal signal, known as the Midsummer drought (MSD), but there is no consensus on which processes are most relevant for the two-peak structure of the rainy season. This paper evaluates three hypotheses that could explain the MSD: the SST cloud-radiative feedback, the solar declination angle and the Caribbean LowLevel Jet (CLLJ) moisture transport hypotheses. Model experiments produced by the Met Office Hadley Centre (MOHC) for CMIP6 as well as ERA5 reanalysis data are used to critically assess the predictions of each hypothesis. The simulations capture the double peak signal of precipitation well and reasonably simulate the spatial and temporal variations of the MSD and other relevant climate features such as the CLLJ. Evidence from our analysis suggests that the Eastern Pacific SSTs do not increase in late summer in ERA5 data and only slightly increase in the simulations. More importantly, the Eastern Pacific SST variability in ERA5 and in the model experiments cannot explain the differences in the seasonality of precipitation. The net shortwave radiation at the surface shows a two-peak seasonal cycle; however, this behaviour appears to result from a strong anti-correlation of the incoming shortwave and convective activity due to cloud radiative-effects. There was no evidence found by this study of a causal link in which absorption of shortwave energy forces precipitation variations, as suggested by the solar declination angle hypothesis. The moisture convergence, CLLJ and the precipitable water vapor variations best explain the characteristics of the observed and simulated MSD, particularly for the onset of the MSD. The diagnosed variations of moisture convergence, which are synchronous with the timing of the MSD, point to a dynamic mechanism in which the low-level inflow from the Caribbean is more important for the MSD than other radiative mechanisms.

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Section: The Role Of the Caribbean Low-level Jetmentioning

confidence: 80%

Section: The Role Of the Caribbean Low-level Jetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Revisiting mechanisms of the Mesoamerican Midsummer drought

García‐Franco

Chadwick

Gray

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Several roles have been attributed to the CLLJ to explain a link between the low-level wind flow over the Caribbean Sea and the MSD in southern Mexico and Central America (see e.g. Gamble et al 2008;Herrera et al 2015;Zermeño-Díaz 2019;Corrales-Suastegui et al 2020). The main dynamical argument that links the MSD and the CLLJ is centred around variations in moisture flux convergence (MFC), and would subsequently influence the mass content of water vapor or total water content (TWC) (see e.g.…”

Section: The Solar Declination Angle Hypothesismentioning

confidence: 99%

“…Since the early analyses of the characteristics of the MSD, research has aimed to understand the physical mechanisms that cause this peculiar two-peak structure of precipitation (e.g., Hastenrath 1967;Magaña et al 1999;Giannini et al 2000;Curtis 2002;Herrera et al 2015;Hidalgo et al 2015;Maldonado et al 2016;Zermeño-Díaz 2019). For instance, Hastenrath (1967) first suggested that a double-crossing of the east Pacific Intertropical Convergence Zone (ITCZ) can explain the MSD, so the first peak of precipitation is associated with the early summer northward crossing of the ITCZ and the second peak with the southward displacement of the ITCZ during late summer.…”

Section: Introductionmentioning

confidence: 99%

Revisiting mechanisms of the Mesoamerican Midsummer drought

et al. 2022

View full text Add to dashboard Cite

Observations show that the seasonal cycle of precipitation in parts of southern Mexico and Central America exhibits a bimodal signal, known as the Midsummer drought (MSD), but there is no consensus on which processes are most relevant for the two-peak structure of the rainy season. This paper evaluates three hypotheses that could explain the MSD: the SST cloud-radiative feedback, the solar declination angle and the Caribbean Low-Level Jet (CLLJ) moisture transport hypotheses. Model experiments produced by the Met Office Hadley Centre (MOHC) for CMIP6 as well as ERA5 reanalysis data are used to critically assess the predictions of each hypothesis. The simulations capture the double peak signal of precipitation well and reasonably simulate the spatial and temporal variations of the MSD and other relevant climate features such as the CLLJ. Evidence from our analysis suggests that the Eastern Pacific SSTs do not increase in late summer in ERA5 data and only slightly increase in the simulations. More importantly, the Eastern Pacific SST variability in ERA5 and in the model experiments cannot explain the differences in the seasonality of precipitation. The net shortwave radiation at the surface shows a two-peak seasonal cycle; however, this behaviour appears to result from a strong anti-correlation of the incoming shortwave and convective activity due to cloud radiative-effects. There was no evidence found by this study of a causal link in which absorption of shortwave energy forces precipitation variations, as suggested by the solar declination angle hypothesis. The moisture convergence, CLLJ and the precipitable water vapor variations best explain the characteristics of the observed and simulated MSD, particularly for the onset of the MSD. The diagnosed variations of moisture convergence, which are synchronous with the timing of the MSD, point to a dynamic mechanism in which the low-level inflow from the Caribbean is more important for the MSD than other radiative mechanisms.

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Quantifying the effects of the diurnal cycle in the variability of rainfall

Zermeño‐Díaz

2021

Intl Journal of Climatology

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In order to quantify how much variability is affected by the diurnal cycle (DC), two variance‐partitioning schemes were applied on two rainfall datasets that cover the Intra Americas Seas (IAS) domain at a 3‐hourly resolution during 21 years. The datasets are the Tropical Rainfall Measurement Mission (TRMM) 3B42, and a simulation from the Centre National de Recherches Météorologiques (CNRM) model. From TRMM, the results show that the variance attributable to the DC is large because it shapes the variability of transients. Such diurnal effects shape transients similarly during all seasons, but their effects produce different patterns over continental and oceanic regions. Over continental regions, the total variance attributable to the DC is much larger than that attributable to the mean seasonal cycle and to interannual variability. But over oceanic regions, the latter two types of partitions can be larger than that of the DC. Although the analysed model simulation captures the broad features of the observed variance partitions, it overestimates the importance of the typical diurnal march, it underestimates how the DC tends to suppresses transient variability during nighttime over land, and it underestimates how it tends to increase it otherwise. As shown by the results, the variance‐partitioning approach of this study might complement previous approaches because rather than focusing on diurnal amplitudes and phases, it focuses on diurnal effects. Therefore, this approach could be useful to diagnose DC‐related issues from a relatively new perspective, issues such as the evaluation of systematic errors, or the evaluation of how the DC affects transients under different large‐scale conditions or slow‐varying forcings.

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The Spatial Pattern of Midsummer Drought as a Possible Mechanistic Response to Lower-Tropospheric Easterlies over the Intra-Americas Seas

Cited by 5 publications

References 43 publications

Revisiting mechanisms of the Mesoamerican Midsummer drought

Revisiting mechanisms of the Mesoamerican Midsummer drought

Revisiting mechanisms of the Mesoamerican Midsummer drought

Quantifying the effects of the diurnal cycle in the variability of rainfall

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