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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Unforced decadal fluctuations in a coupled model of the atmosphere and ocean mixed layer

Global average temperature in a 100-year control run of a model used for greenhouse gas response simulations showed low-frequency natural variability comparable in magnitude to that observed over the last 100 years. The model variability was found to be barotropic in the atmosphere, and located in the tropical strip with largest values near the equator in the Pacific. The model variations were traced to complex, low-frequency interactions between the meridional sea surface temperature gradients in the eastern equatorial Pacific, clouds at both high and low levels, and features of the tropical atmospheric circulation. The variations in these and other model parameters appear to oscillate between two limiting climate states. The physical scenario accounting for the oscillations on decadal time scales is almost certainly not found in the real world on shorter time scales due to limited resolution and the omission of key physics (e.g., equatorial ocean dynamics) in the model. The real message is that models with dynamical limitations can still produce significant long-term variability. Only a thorough physical diagnosis of such simulations and comparisons with decadal-length data sets will allow one to decide if faith in the model results is, or is not, warranted.

Barnett, T. P.↗
NASA NTRS2011

El Nino-Southern Oscillation Correlated Aerosol Angstrom Exponent Anomaly Over the Tropical Pacific Discovered in Satellite Measurements

El Nino.Southern Oscillation (ENSO) is the dominant mode of interannual variability in the tropical atmosphere. ENSO could potentially impact local and global aerosol properties through atmospheric circulation anomalies and teleconnections. By analyzing aerosol properties, including aerosol optical depth (AOD) and Angstrom exponent (AE; often used as a qualitative indicator of aerosol particle size) from the Moderate Resolution Imaging Spectrometer, the Multiangle Imaging Spectroradiometer and the Sea ]viewing Wide Field ]of ]view Sensor for the period 2000.2011, we find a strong correlation between the AE data and the multivariate ENSO index (MEI) over the tropical Pacific. Over the western tropical Pacific (WTP), AE increases during El Nino events and decreases during La Nina events, while the opposite is true over the eastern tropical Pacific (ETP). The difference between AE anomalies in the WTP and ETP has a higher correlation coefficient (>0.7) with the MEI than the individual time series and could be considered another type of ENSO index. As no significant ENSO correlation is found in AOD over the same region, the change in AE (and hence aerosol size) is likely to be associated with aerosol composition changes due to anomalous meteorological conditions induced by the ENSO. Several physical parameters or mechanisms that might be responsible for the correlation are discussed. Preliminary analysis indicates surface wind anomaly might be the major contributor, as it reduces sea ]salt production and aerosol transport during El Nino events. Precipitation and cloud fraction are also found to be correlated with tropical Pacific AE. Possible mechanisms, including wet removal and cloud shielding effects, are considered. Variations in relative humidity, tropospheric ozone concentration, and ocean color during El Nino have been ruled out. Further investigation is needed to fully understand this AE ]ENSO covariability and the underlying physical processes responsible for it.

Li, Jing↗
DOE OSTI2020

A Hindcast Approach to Diagnosing the Equatorial Pacific Cold Tongue SST Bias in CESM1

An ensemble seasonal hindcast approach is used to investigate the development of the equatorial Pacific Ocean cold sea surface temperature (SST) bias and its characteristic annual cycle in the Community Earth System Model, version 1 (CESM1). In observations, eastern equatorial Pacific SSTs exhibit a warm phase during boreal spring and a cold phase during late boreal summer–autumn. The CESM1 climatology shows a cold bias during both warm and cold phases. In our hindcasts, the cold bias during the cold phase develops in less than 6 months, whereas the cold bias during the warm phase takes longer to emerge. The fast-developing cold-phase cold bias is associated with too-strong vertical advection and easterly wind stress over the eastern equatorial region. The antecedent boreal summer easterly wind anomalies also appear in atmosphere-only simulations, indicating that the errors are intrinsic to the atmosphere component. For the slower-developing warm-phase cold bias, we find that the too-cold SSTs over the equatorial region are associated with a slowly evolving upward displacement of subsurface ocean zonal currents and isotherms that can be traced to the ocean component.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

Moisture bursts over the tropical Pacific Ocean

The frequency and location of moisture bursts are examined. A moisture burst is described and defined, and this definition is applied to IR imagery for four six-month cool seasons (November-April) in the eastern North Pacific. It is observed that about ten moisture bursts/month occur during the cool seasons; the bursts last about 2-4 days and no more than 10 days; and they are distributed uniformly across the Pacific to the west of 110 deg W. The relation between the moisture bursts and the El Nino event of 1982-1983, and moisture bursts in the general circulation are analyzed. The analyses reveal that few bursts occur in the region associated with the El Nino event, and the moisture bursts resemble transient intensification of the mean meridional circulation in regions with a weak Hadley cell. Two modes for the behavior of the Hadley cell in the Pacific are proposed.

Mcguirk, James P.↗
NASA NTRS1986

Rainfall over oceans inferred from Nimbus 7 SMMR - Application to 1982-83 El Nino

Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) measurements at five frequencies in the region 6.6 to 37 GHz, at a resolution of 155 km, are analyzed to infer precipitation over the global oceans. The microwave data show, on this spatial scale, that the combined liquid water in the clouds and rain increases the brightness temperature almost linearly with frequency in the 6.6-18-GHz region, while at 37 GHz such a simple relationship is not noticed. Further, as the atmospheric water-vapor absorption and the effects of scattering by precipitation particles are relatively weak at 6.6 and 10.7 GHz, a technique to remotely sense the liquid water content in the atmosphere is developed based on the brightness measurements at these two frequencies. Seasonal mean patterns of liquid water content in the atmosphere derived from SMMR over global oceans relate closely to climatological patterns of precipitation. Based on this, an empirical relationship is derived to estimate precipitation over the global oceans, with an accuracy of about + or - 30 percent, on a seasonal basis from satellite measurements made during the three years (1979-81) before the recent El Nino event. The deviations from these three-year means, in the precipitation, produced by the 1982-83 el Nino event are then deduced from the SMMR measurements. In the Pacific, the precipitation over the ITCZ in the north, the South Pacific Convergence Zone, and the oceans around Indonesia is drastically reduced. At the same time a substantial increase in precipitation is observed over the normally dry central and eastern equatorial Pacific Ocean.

Prabhakara, C.↗
NASA NTRS1999

El Nino and the Global Ocean Observing System

Until a decade ago, an often-quoted expression in oceanography is that very few observations are recorded throughout the ocean. Now, the sentiment is no longer valid in the uppermost 10% of the tropical Pacific Ocean nor at the surface of the global ocean. One of the remarkable legacies of the 1985-1994 Tropical Oceans Global Atmosphere (TOGA) Program is an in situ marine meteorological and upper oceanographic measurement array throughout the equatorial Pacific to monitor the development and maintenance of El Nino episodes. The TOGA Observing System, which initially consisted of moored- and drifting-buoy arrays, a network of commercial ships, and coastal and island stations, now includes a constellation of satellites and data-assimilating models to simulate subsurface oceanographic conditions. The El Nino and La Nina tropical Pacific Ocean observing system represents the initial phase of an integrated global ocean observing system. Remarkable improvements have been made in ocean model simulation of subsurface currents, but some problems persist. For example, the simulation of the South Equatorial Current (SEC) remains an important challenge in the 2S-2N Pacific equatorial wave guide. During El Nino the SEC at the equator is reduced and sometimes the direction is reversed, becoming eastward. Both conditions allow warm water stored in the western Pacific to invade the eastern region, creating an El Nino episode. Assimilation of data is a tenet of faith to correct simulation errors caused by deficiencies in surface fluxes (especially wind stress) and parameterizations of subgrid-scale physical processes. In the first of two numerical experiments, the Pacific SEC was simulated with and without assimilation of subsurface temperature data. Along the equator, a very weak SEC occurred throughout the eastern Pacific, independent of assimilation of data. However, as displayed in the diagram, in the western Pacific there was no satisfactory agreement between the two simulations. To help determine reliability of the simulated SEC in the western Pacific, current measurements recorded during the 9-19 October 1994 voyage of the French research vessel L'Atalante are also shown in the diagram. With data assimilation, the simulated SEC was in much better agreement with L'Atalante observations. The simulated SEC with data assimilation was far from perfect, in part because of the sparsity of subsurface temperature observations. In the next experiment, TOPEX/POSEIDON sea surface height data in combination with subsurface temperatures will be assimilated to assess further improvement of the simulation of the SEC.

Halpern, David↗
NASA NTRS2016

Western Pacific Hydroclimate Linked to Global Climate Variability Over the Past Two Millennia

Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between B1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between B1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.

Pacific Ocean↗
NASA NTRS2002

Variability in Ozone in the Tropical Tropopause Region from the 1998-2000 SHADOZ (Southern Hemisphere ADditional OZonesondes) Data

The first view of stratospheric and tropospheric ozone variability in the southern hemisphere tropics is provided by a 3-year, 10-site record of ozone soundings from the Southern Hemisphere ADditional OZonesondes (SHADOZ) network. Observations covering 1998-2000 were made over Ascension Island; Nairobi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; Natal, Brazil. Taking the TTL (tropical tropopause layer) as the region between 12 and 17 km, we examine ozone variability in this region on a week-to-week and seasonal basis. The TTL layer is lower in September-October-November than in March-April-May, when ozone is a minimum at most SHADOZ stations. A zonal wave-one pattern is apparent in column-integrated TTL ozone because ozone mixing ratios are greater over the Atlantic and adjacent continents than over the Pacific and eastern Indian Ocean. The wave-one persists all year with varying magnitude and appears to be due to general circulation - with subsidence over the Atlantic and frequent deep convection over the Pacific and Indian Ocean. The variability of deep convection - most prominent at Java, Fiji, Samoa and Natal - is explored in time-vs-altitude ozone curtains. Stratospheric incursions into the troposphere are most prominent in soundings at Irene and Reunion Island.

Thompson, Anne M.↗
NASA NTRS2002

Variability in Ozone in the Tropical Upper Troposphere-Lower Stratosphere from the 1998-2000 SHADOZ (Southern Hemisphere Additional Ozonesondes) Data

The first view of lower stratospheric and upper tropospheric structure from sondes is provided by a 3-year, 10-site record from the Southern Hemisphere ADditional OZonesondes (SHADOZ) network: . Observations covering 1998-2000 were made over Ascension Island; Nairobi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; Natal, Brazil. Taking the UT/LS (upper troposphere- lower stratosphere) as the region between 12 and 17 km, we examine ozone variability in this region on a week-to-week and seasonal basis. The tropopause is lower in September-October-November than in March-April-May, when ozone is a minimum at most SHADOZ stations. A zonal wave-one pattern (referring to ozone mixing ratios greater over the Atlantic and adjacent continents than over the Pacific and eastern Indian Ocean), persists all year. The wave, predominantly in the troposphere and with variable magnitude, appears to be due to general circulation - with subsidence over the Atlantic and frequent deep convection over the Pacific and Indian Ocean. The variability of deep convection most prominent at Java, Fiji, Samoa and Natal - is explored in time-vs-altitude ozone curtains. Stratospheric incursions into the troposphere are most prominent in soundings at Irene and Reunion Island.

Thompson, A. M.↗
NASA NTRS2002

Insights into Tropical Tropospheric Ozone from the SHADOZ Network

The first view of lower stratospheric and upper tropospheric structure from sondes is provided by a 3-year, 10-site record from the Southern Hemisphere ADditional OZonesondes (SHADOZ) network: http://code9 16.gsfc.nasa.gov/Data_services/shadoz. Observations covering 1998-2000 were made over Ascension Island; Nairobi, Kenya; Irene, South Africa; La Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; Natal, Brazil. Taking the UT/LS (upper troposphere-lower stratosphere) as the region between 12 and 17 km, we examine ozone variability in this region on a week-to- week and seasonal basis. The tropopause is lower in September-October-November than in March-April-May, when ozone is a minimum at most SHADOZ stations. A zonal wave-one pattern (referring to ozone mixing ratios greater over the Atlantic and adjacent continents than over the Pacific and eastern Indian Ocean), persists all year. The wave, predominantly in the troposphere and with variable magnitude, appears to be due to general circulation - with subsidence over the Atlantic and frequent deep convection over the Pacific and Indian Ocean. The variability of deep convection - most prominent at Java, Fiji, Samoa and Natal - is explored in time-vs-altitude ozone curtains. Stratospheric incursions into the troposphere are most prominent in soundings at Irene and Reunion Island.

Thompson, A. M.↗
DOE OSTI2023

On the relationship between eastern China aerosols and western North Pacific tropical cyclone activity

How aerosols affect the weather and climate system has received increasing attention. This study finds a significant negative correlation between March–May eastern China aerosol optical depth (AOD) and July–November western North Pacific (WNP) tropical cyclone (TC) frequency during 2003–2020. This time period spans when several aerosol reanalyses are available and both Terra and Aqua Moderate Resolution Imaging Spectroradiometer AOD retrievals are assimilated therein. Composite analyses and budget analyses of dynamical genesis potential indices indicate the importance of large-scale environmental factors, especially vertical velocity and vertical wind shear, associated with changes in AOD that in turn modulate changes in WNP TC frequency. Increased eastern China AOD may facilitate negative Pacific meridional mode development via modulation of the westerly jet, which then forces an anticyclonic circulation over the WNP basin. Increased AOD can also directly decrease the inter-hemispheric temperature differential and increases the intra-hemispheric temperature differential between the equator and the mid-latitudes, thus weakening ascending motion and enhancing vertical wind shear over the WNP, especially the southeastern portion of the basin. Further, all of these large-scale environment changes induced by increased eastern China AOD tend to suppress WNP TCs. This study highlights the potential influence of eastern China aerosol loadings on WNP TCs, thus improving our understanding of TC climate variability over the WNP.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

Can TOPEX/Poseidon Data be Used for Monitoring the Indonesian Throughflow?

The effects of the Indonesian throughflow(ITF) are studied in a reduced gravity, primitive equation, sigma coordinate model. The surface heat fluxes are provided by coupling the ocean GCAF to an advective atmospheric mixed layer model. There is an ENSO related signal in the ITF but the correlation with the Southern Oscillation Index (SOI) is only -0.31. When the winds over the Indian Ocean are held to climatology, this correlation jumps to -0.65 indicating that the non-EASO signal in the ITF is caused by the downstream winds. On interannual time-scales the ITF can be explained in terms of sea level differences between the western Pacific and eastern Indian Oceans when appropriate representative locations are chosen as demonstrated in both model and TOPEX data. It is shown that the main climatological effect of the ITF is to warm the Indian Ocean and cool the Pacific. Mile the main ENSO indices, NIN03 and NIN04, are almost identical with and without the ITF, the total SSTs show significant ENSO dependence.

Murtugudde, Ragu↗
NASA NTRS2019

A Global Climatology of Extratropical Transition Part I: Characteristics Across Basins

The authors present a global climatology of tropical cyclones (TCs) that undergo extratropical transition (ET). ET is objectively defined based on a TC's trajectory through the cyclone phase space (CPS), which is calculated using storm tracks from 1979-2017 best-track data and geopotential height fields from reanalysis datasets. Two reanalyses are used and compared for this purpose, the Japanese 55-year Reanalysis and the ECMWF Interim Reanalysis. The results are used to study the seasonal and geographical distributions of storms undergoing ET and inter-basin differences in the statistics of ET occurrence. About 50% of all TCs in the North Atlantic and the Western North Pacific undergo ET. In the southern hemisphere, ET fractions range from about 20% in the South Indian Ocean and the Australian region to 45% in the South Pacific. In the majority of ETs, TCs become thermally asymmetric before forming a cold core. However, a substantial fraction of TCs takes the reverse pathway, developing a cold core before becoming thermally asymmetric. This pathway is most common in the Eastern North Pacific and the North Atlantic. Different ET pathways can be linked to different geographical trajectories and environmental settings. In ETs over warmer sea-surface temperatures, TCs tend to lose their thermal symmetry while still maintaining a warm core. Landfalls by TCs undergoing ET occur 3-4 times per year in the North Atlantic and 7-10 times per year in the Western North Pacific, while coastal regions in the Australian region are affected once every 1-2 years.

Melanie Bieli↗
NASA NTRS1994

The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

Chen, Dake↗
DOE OSTI2023

Volcanic forcing degrades multiyear-to-decadal prediction skill in the tropical Pacific

Volcanic aerosol forcing can affect global climate, but its role in climate prediction remains poorly understood. We isolate the impact of volcanic eruptions on multiyear-to-decadal climate prediction skill by comparing two suites of initialized decadal hindcasts conducted with and without historical volcanic forcing. Unexpectedly, the inclusion of volcanic forcing in the prediction system significantly degrades the forecast skill of detrended multiyear-to-decadal sea surface temperature (SST) variability in the central-eastern tropical Pacific. The ensemble mean hindcasts produce multiyear-to-decadal tropical Pacific SST cooling in response to large tropical volcanic eruptions through thermodynamic and El Niño–Southern Oscillation (ENSO)–like dynamic processes. However, in observations, these eruptions coincided with tropical Pacific warming, which is well predicted by the no-volcano hindcasts and, hence, is likely related to internal climate variability. Improved model representation of volcanic response and its interaction with internal climate variability is required to advance prediction of tropical Pacific decadal variability and associated global impacts.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1988

Analyses of the wind-driven response of tropical oceans

Numerical and analytical models are used to study the upper-ocean response to surface wind stress estimates from the tropical Atlantic and Pacific Oceans. These models are used to identify regions of important variability in the wind field, analyze the oceanic response, and demonstrate the applicability of remotely sensed vector wind stress and altimetry data. Both model and XBT depictions of the mean seasonal cycle, 1979 to 1981, were analyzed along the major ship tracks in the western, central, and eastern tropical Pacific. Model solutions were also used to address array design questions in observing system simulation experiments. Subsequent analyses of the 1982 to 1983 solutions will be performed with respect to differences from the mean seasonal cycle 1979 to 1981, as well as, differences in the three wind products.

Busalacchi, A. J.↗
NASA NTRS1996

Responses of the Tropical Pacific to Wind Forcing as Observed by Spaceborne Sensors and Simulated by an Ocean General Circulation Model

In this study, satellite observations, in situ measurements, and model simulations are combined to assess the oceanic response to surface wind forcing in the equatorial Pacific. The surface wind fields derived from observations by the spaceborne special sensor microwave imager (SSM/I) and from the operational products of the European Centre for Medium-Range Weather Forecasts (ECMWF) are compared. When SSM/I winds are used to force a primitive-equation ocean general circulation model (OGCM), they produce 3 C more surface cooling than ECMWF winds for the eastern equatorial Pacific during the cool phase of an El Nino-Southern Oscillation event. The stronger cooling by SSM/I winds is in good agreement with measurements at the moored buoys and observations by the advanced very high resolution radiometer, indicating that SSM/I winds are superior to ECMWF winds in forcing the tropical ocean. In comparison with measurements from buoys, tide gauges, and the Geosat altimeter, the OGCM simulates the temporal variations of temperature, steric, and sea level changes with reasonable realism when forced with the satellite winds. There are discrepancies between model simulations and observations that are common to both wind forcing fields, one of which is the simulation of zonal currents; they could be attributed to model deficiencies. By examining model simulations under two winds, vertical heat advection and uplifting of the thermocline are found to be the dominant factors in the anomalous cooling of the ocean mixed layer.

Liu, W. Timothy↗
NASA NTRS2016

The Mexican Drought Atlas: Tree-Ring Reconstructions of the Soil Moisture Balance During the Late Pre-Hispanic, Colonial, and Modern Eras

Mexico has suffered a long history and prehistory of severe sustained drought. Drought over Mexico is modulated by ocean-atmospheric variability in the Atlantic and Pacific, raising the possibility for long-range seasonal climate forecasting, which could help mediate the economic and social impacts of future dry spells. The instrumental record of Mexican climate is very limited before 1920, but tree-ring chronologies developed from old-growth forests in Mexico can provide an excellent proxy representation of the spatial pattern and intensity of past moisture regimes useful for the analysis of climate dynamics and climate impacts. The Mexican Drought Atlas (MXDA) has been developed from an extensive network of 252 climate sensitive tree-ring chronologies in and near Mexico. The MXDA reconstructions extend from 1400 CE-2012 and were calibrated with the instrumental summer (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) on a 0.5deg latitude/longitude grid extending over land areas from 14 to 34degN and 75-120degW using Ensemble Point-by-Point Regression (EPPR) for the 1944-1984 period. The grid point reconstructions were validated for the period 1920-1943 against instrumental gridded scPDSI values based on the fewer weather station observations available during that interval. The MXDA provides a new spatial perspective on the historical impacts of moisture extremes over Mexico during the past 600-years, including the Aztec Drought of One Rabbit in 1454, the drought of El Ano de Hambre in 1785-1786, and the drought that preceded the Mexican Revolution of 1909-1910. The El Nino/Southern Oscillation (ENSO) is the most important ocean-atmospheric forcing of moisture variability detected with the MXDA. In fact, the reconstructions suggest that the strongest central equatorial Pacific sea surface temperature (SST) teleconnection to the soil moisture balance over North America may reside in northern Mexico. This ENSO signal has stronger and more time-stable correlations than computed for either the Atlantic Multidecadal Oscillation or Pacific Decadal Oscillation. The extended Multivariate ENSO Index is most highly correlated with reconstructed scPDSI over northern Mexico, where warm events favor moist conditions during the winter, spring, and early summer. This ENSO teleconnection to northern Mexico has been strong over the past 150 years, but it has been comparatively weak and non-stationary in the MXDA over central and southern Mexico where eastern tropical Pacific and Caribbean/tropical Atlantic SSTs seem to be more important. The ENSO teleconnection to northern Mexico is weaker in the available instrumental PDSI, but analyses based on the millennium climate simulations with the Community Earth System Model suggest that the moisture balance during the winter, spring, and early summer over northern Mexico may indeed be particularly sensitive to ENSO forcing. Nationwide drought is predicted to become more common with anthropogenic climate change, but the MXDA reconstructions indicate that intense "All Mexico" droughts have been rare over the past 600 years and their frequency does not appear to have increased substantially in recent decades.

El Nino↗