scholarly journals The effects of ENSO and the North American monsoon on mast seeding in two Rocky Mountain conifer species

2021 ◽  
Vol 376 (1839) ◽  
Author(s):  
Andreas P. Wion ◽  
Ian S. Pearse ◽  
Kyle C. Rodman ◽  
Thomas T. Veblen ◽  
Miranda D. Redmond
Keyword(s):  
Pinus Ponderosa ◽  
North American ◽  
Large Scale ◽  
Southern Oscillation ◽  
Mast Seeding ◽  
North American Monsoon ◽  
Climate Indices ◽  
Conifer Species ◽  
Cone Production ◽  
The North

We aimed to disentangle the patterns of synchronous and variable cone production (i.e. masting) and its relationship to climate in two conifer species native to dry forests of western North America. We used cone abscission scars to reconstruct ca 15 years of recent cone production in Pinus edulis and Pinus ponderosa , and used redundancy analysis to relate time series of annual cone production to climate indices describing the North American monsoon and the El Niño Southern Oscillation (ENSO). We show that the sensitivity to climate and resulting synchrony in cone production varies substantially between species. Cone production among populations of P. edulis was much more spatially synchronous and more closely related to large-scale modes of climate variability than among populations of P. ponderosa . Large-scale synchrony in P. edulis cone production was associated with the North American monsoon and we identified a dipole pattern of regional cone production associated with ENSO phase. In P. ponderosa , these climate indices were not strongly associated with cone production, resulting in asynchronous masting patterns among populations. This study helps frame our understanding of mast seeding as a life-history strategy and has implications for our ability to forecast mast years in these species. This article is part of the theme issue ‘The ecology and evolution of synchronized seed production in plants’.

scholarly journals Toward Assessing NARCCAP Regional Climate Model Credibility for the North American Monsoon: Future Climate Simulations*

2015 ◽  
Vol 28 (17) ◽  
pp. 6707-6728 ◽  
Author(s):  
Melissa S. Bukovsky ◽  
Carlos M. Carrillo ◽  
David J. Gochis ◽  
Dorit M. Hammerling ◽  
Rachel R. McCrary ◽  
...  
Keyword(s):  
Climate Change ◽  
North American ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Regional Climate ◽  
Global Climate Models ◽  
North American Monsoon ◽  
The North ◽  
Climate Simulations ◽  
Projected Changes

Abstract This study presents climate change results from the North American Regional Climate Change Assessment Program (NARCCAP) suite of dynamically downscaled simulations for the North American monsoon system in the southwestern United States and northwestern Mexico. The focus is on changes in precipitation and the processes driving the projected changes from the regional climate simulations and their driving coupled atmosphere–ocean global climate models. The effect of known biases on the projections is also examined. Overall, there is strong ensemble agreement for a large decrease in precipitation during the monsoon season; however, this agreement and the magnitude of the ensemble-mean change is likely deceiving, as the greatest decreases are produced by the simulations that are the most biased in the baseline/current climate. Furthermore, some of the greatest decreases in precipitation are being driven by changes in processes/phenomena that are less credible (e.g., changes in El Niño–Southern Oscillation, when it is initially not simulated well). In other simulations, the processes driving the precipitation change may be plausible, but other biases (e.g., biases in low-level moisture or precipitation intensity) appear to be affecting the magnitude of the projected changes. The most and least credible simulations are clearly identified, while the other simulations are mixed in their abilities to produce projections of value.

scholarly journals Assessment of CMIP5 Model Simulations of the North American Monsoon System

2013 ◽  
Vol 26 (22) ◽  
pp. 8787-8801 ◽  
Author(s):  
Kerrie L. Geil ◽  
Yolande L. Serra ◽  
Xubin Zeng
Keyword(s):  
North American ◽  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
North American Monsoon ◽  
Monthly Precipitation ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Monsoon System

Abstract Precipitation, geopotential height, and wind fields from 21 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined to determine how well this generation of general circulation models represents the North American monsoon system (NAMS). Results show no improvement since CMIP3 in the magnitude (root-mean-square error and bias) of the mean annual cycle of monthly precipitation over a core monsoon domain, but improvement in the phasing of the seasonal cycle in precipitation is notable. Monsoon onset is early for most models but is clearly visible in daily climatological precipitation, whereas monsoon retreat is highly variable and unclear in daily climatological precipitation. Models that best capture large-scale circulation patterns at a low level usually have realistic representations of the NAMS, but even the best models poorly represent monsoon retreat. Difficulty in reproducing monsoon retreat results from an inaccurate representation of gradients in low-level geopotential height across the larger region, which causes an unrealistic flux of low-level moisture from the tropics into the NAMS region that extends well into the postmonsoon season. Composites of the models with the best and worst representations of the NAMS indicate that adequate representation of the monsoon during the early to midseason can be achieved even with a large-scale circulation pattern bias, as long as the bias is spatially consistent over the larger region influencing monsoon development; in other words, as with monsoon retreat, it is the inaccuracy of the spatial gradients in geopotential height across the larger region that prevents some models from realistic representation of the early and midseason monsoon system.

scholarly journals Multiscale Variability of the Flow during the North American Monsoon Experiment

2007 ◽  
Vol 20 (9) ◽  
pp. 1628-1648 ◽  
Author(s):  
Richard H. Johnson ◽  
Paul E. Ciesielski ◽  
Brian D. McNoldy ◽  
Peter J. Rogers ◽  
Richard K. Taft
Keyword(s):  
United States ◽  
North American ◽  
Gulf Of California ◽  
Large Scale ◽  
Regional Scale ◽  
North American Monsoon ◽  
Return Flow ◽  
Southwestern United States ◽  
The North ◽  
Upper Level

Abstract The 2004 North American Monsoon Experiment (NAME) provided an unprecedented observing network for studying the structure and evolution of the North American monsoon. This paper focuses on multiscale characteristics of the flow during NAME from the large scale to the mesoscale using atmospheric sounding data from the enhanced observing network. The onset of the 2004 summer monsoon over the NAME region accompanied the typical northward shift of the upper-level anticyclone or monsoon high over northern Mexico into the southwestern United States, but in 2004 this shift occurred slightly later than normal and the monsoon high did not extend as far north as usual. Consequently, precipitation over the southwestern United States was slightly below normal, although increased troughiness over the Great Plains contributed to increased rainfall over eastern New Mexico and western Texas. The first major pulse of moisture into the Southwest occurred around 13 July in association with a strong Gulf of California surge. This surge was linked to the westward passages of Tropical Storm Blas to the south and an upper-level inverted trough over northern Texas. The development of Blas appeared to be favored as an easterly wave moved into the eastern Pacific during the active phase of a Madden–Julian oscillation. On the regional scale, sounding data reveal a prominent sea breeze along the east shore of the Gulf of California, with a deep return flow as a consequence of the elevated Sierra Madre Occidental (SMO) immediately to the east. Subsidence produced a dry layer over the gulf, whereas a deep moist layer existed over the west slopes of the SMO. A prominent nocturnal low-level jet was present on most days over the northern gulf. The diurnal cycle of heating and moistening (Q1 and Q2) over the SMO was characterized by deep convective profiles in the mid- to upper troposphere at 1800 LT, followed by stratiform-like profiles at midnight, consistent with the observed diurnal evolution of precipitation over this coastal mountainous region. The analyses in the core NAME domain are based on a gridded dataset derived from atmospheric soundings only and, therefore, should prove useful in validating reanalyses and regional models.

Can a Regional Climate Model Improve the Ability to Forecast the North American Monsoon?

2012 ◽  
Vol 25 (23) ◽  
pp. 8212-8237 ◽  
Author(s):  
Christopher L. Castro ◽  
Hsin-I Chang ◽  
Francina Dominguez ◽  
Carlos Carrillo ◽  
Jae-Kyung Schemm ◽  
...  
Keyword(s):  
North American ◽  
Large Scale ◽  
Dynamical Downscaling ◽  
Warm Season ◽  
Regional Model ◽  
Precipitation Anomaly ◽  
Early Summer ◽  
North American Monsoon ◽  
The North ◽  
Temperature And Precipitation

Abstract Global climate models are challenged to represent the North American monsoon, in terms of its climatology and interannual variability. To investigate whether a regional atmospheric model can improve warm season forecasts in North America, a retrospective Climate Forecast System (CFS) model reforecast (1982–2000) and the corresponding NCEP–NCAR reanalysis are dynamically downscaled with the Weather Research and Forecasting model (WRF), with similar parameterization options as used for high-resolution numerical weather prediction and a new spectral nudging capability. The regional model improves the climatological representation of monsoon precipitation because of its more realistic representation of the diurnal cycle of convection. However, it is challenged to capture organized, propagating convection at a distance from terrain, regardless of the boundary forcing data used. Dynamical downscaling of CFS generally yields modest improvement in surface temperature and precipitation anomaly correlations in those regions where it is already positive in the global model. For the North American monsoon region, WRF adds value to the seasonally forecast temperature only in early summer and does not add value to the seasonally forecast precipitation. CFS has a greater ability to represent the large-scale atmospheric circulation in early summer because of the influence of Pacific SST forcing. The temperature and precipitation anomaly correlations in both the global and regional model are thus relatively higher in early summer than late summer. As the dominant modes of early warm season precipitation are better represented in the regional model, given reasonable large-scale atmospheric forcing, dynamical downscaling will add value to warm season seasonal forecasts. CFS performance appears to be inconsistent in this regard.

scholarly journals Simulation of the North American Monsoon by the NCAR CCM3 and Its Sensitivity to Convection Parameterization

2006 ◽  
Vol 19 (12) ◽  
pp. 2851-2866 ◽  
Author(s):  
J. Craig Collier ◽  
Guang J. Zhang
Keyword(s):  
Relative Humidity ◽  
Diurnal Cycle ◽  
North American ◽  
Large Scale ◽  
The United States ◽  
Experimental Simulation ◽  
Specific Humidity ◽  
North American Monsoon ◽  
Hourly Precipitation ◽  
The North

Abstract Two 9-yr runs of the NCAR Community Climate Model version 3 (CCM3) are compared in their simulations of the North American summer monsoon. In a control simulation, the Zhang–McFarlane deep convection scheme is used. For an experimental simulation, the following modifications to the scheme are implemented. The closure is based on the large-scale forcing of virtual temperature, and a relative humidity threshold on convective parcels lifted from the boundary layer is applied. The sensitivity to these modifications for simulating the North American monsoon is investigated. Model validation relies on hourly precipitation rates from surface gauges over the United States, hourly precipitation rates derived from the combination of microwave and radar measurements from NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite over Mexico, and CAPE values as calculated from temperature, specific humidity, and pressure fields from the NCEP–NCAR reanalysis. Results show that the experimental run improves the timing of the monsoon onset and peak in the regions of core monsoon influence considered here, though it increases a negative bias in the peak monsoon intensity in one region of northern Mexico. Sensitivity of the diurnal cycle of precipitation to modifications in the convective scheme is highly geographically dependent. Using a combination of gauge-based rainfall rates and reanalysis-based CAPE, it is found that improvements in the simulated diurnal cycle are confined to a convective regime in which the diurnal evolution of precipitation is observed to lag that of CAPE. For another regime, in which CAPE is observed to be approximately in phase with precipitation, model phase biases increase nearly everywhere. Some of the increased phase biases in the latter regime are primarily because of application of the relative humidity threshold.

scholarly journals Effects of Increased Horizontal Resolution on Simulation of the North American Monsoon in the NCAR CAM3: An Evaluation Based on Surface, Satellite, and Reanalysis Data

2007 ◽  
Vol 20 (9) ◽  
pp. 1843-1861 ◽  
Author(s):  
J. Craig Collier ◽  
Guang J. Zhang
Keyword(s):  
North American ◽  
Large Scale ◽  
Monsoon Season ◽  
The United States ◽  
Horizontal Resolution ◽  
North American Monsoon ◽  
Sierra Madre Occidental ◽  
The North ◽  
Sierra Madre ◽  
Monsoon System

Abstract Simulation of the North American monsoon system by the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM3) is evaluated in its sensitivity to increasing horizontal resolution. For two resolutions, T42 and T85, rainfall is compared to Tropical Rainfall Measuring Mission (TRMM) satellite-derived and surface gauge-based rainfall rates over the United States and northern Mexico as well as rainfall accumulations in gauges of the North American Monsoon Experiment (NAME) Enhanced Rain Gauge Network (NERN) in the Sierra Madre Occidental. Simulated upper-tropospheric mass and wind fields are compared to those from NCEP–NCAR reanalyses. The comparison presented herein demonstrates that tropospheric motions associated with the North American monsoon system are sensitive to increasing the horizontal resolution of the model. An increase in resolution from T42 to T85 results in changes to a region of large-scale midtropospheric descent found north and east of the monsoon anticyclone. Relative to its simulation at T42, this region extends farther south and west at T85. Additionally, at T85, the subsidence is stronger. Consistent with the differences in large-scale descent, the T85 simulation of CAM3 is anomalously dry over Texas and northeastern Mexico during the peak monsoon months. Meanwhile, the geographic distribution of rainfall over the Sierra Madre Occidental region of Mexico is more satisfactorily simulated at T85 than at T42 for July and August. Moisture import into this region is greater at T85 than at T42 during these months. A focused study of the Sierra Madre Occidental region in particular shows that, in the regional-average sense, the timing of the peak of the monsoon is relatively insensitive to the horizontal resolution of the model, while a phase bias in the diurnal cycle of monsoon season precipitation is somewhat reduced in the higher-resolution run. At both resolutions, CAM3 poorly simulates the month-to-month evolution of monsoon rainfall over extreme northwestern Mexico and Arizona, though biases are considerably improved at T85.

scholarly journals Convective forcing of the North American Monsoon Anticyclone at intraseasonal and interannual time scales

2021 ◽  
Author(s):  
Kai-Wei Chang ◽  
Kenneth P. Bowman ◽  
Leong Wai Siu ◽  
Anita D. Rapp
Keyword(s):  
Time Scales ◽  
North American ◽  
Time Scale ◽  
General Circulation ◽  
Large Scale ◽  
Vertical Structure ◽  
Lower Stratosphere ◽  
North American Monsoon ◽  
The North ◽  
Circulation Anomalies

AbstractIn the upper troposphere and lower stratosphere (UTLS), large-scale anticyclones associated with monsoons play major roles in tropospheric and stratospheric transport and mixing. To understand the forcing of the North American Monsoon Anticyclone (NAMA), this study examines the connection between precipitation over the tropics and subtropics of the North American longitude sector and the variability of the troposphere and lower stratosphere. Using ERA5 reanalysis and outgoing longwave radiation (OLR) data from 1979 to 2019, we assess the relationship at the intraseasonal time scale using pentad-mean time series. We show that OLR anomalies are correlated with circulation anomalies northwest and northeast of the region of precipitation. Decreased OLR (increased precipitation) corresponds to increased geopotential heights and anticyclonic circulation anomalies in the 300 – 100 hPa layer and an opposite response in the lower tropospheric 850 – 600 hPa layer. The results are consistent with the established theory of the Rossby wave response to latent heating. The increase in height, which is strongest near 150 hPa, indicates that increased precipitation is associated with a strengthened NAMA. UTLS temperatures also have significant correlations with OLR, with cold (warm) anomalies occurring above (below) the core of the anticyclonic anomaly consistent with large-scale balance. The vertical structure of geopotential and temperature anomalies is compared to simulations using an idealized general circulation model, which shows that such a vertical structure is a consistent response to diabatic heating. Correlations at the interannual time scale resemble those at the intraseasonal time scale, demonstrating that precipitation is related to the NAMA at both time scales.

scholarly journals Flash Flooding in Arid/Semiarid Regions: Climatological Analyses of Flood-Producing Storms in Central Arizona during the North American Monsoon

2019 ◽  
Vol 20 (7) ◽  
pp. 1449-1471 ◽  
Author(s):  
Long Yang ◽  
James Smith ◽  
Mary Lynn Baeck ◽  
Efrat Morin
Keyword(s):  
United States ◽  
North American ◽  
Large Scale ◽  
North American Monsoon ◽  
Time Variability ◽  
Southwestern United States ◽  
Flash Flooding ◽  
The North ◽  
Synoptic Conditions ◽  
Central Arizona

Abstract Flash flooding in the arid/semiarid southwestern United States is frequently associated with convective rainfall during the North American monsoon. In this study, we examine flood-producing storms in central Arizona based on analyses of dense rain gauge observations and stream gauging records as well as North American Regional Reanalysis fields. Our storm catalog consists of 102 storm events during the period of 1988–2014. Synoptic conditions for flood-producing storms are characterized based on principal component analyses. Four dominant synoptic modes are identified, with the first two modes explaining approximately 50% of the variance of the 500-hPa geopotential height. The transitional synoptic pattern from the North American monsoon regime to midlatitude systems is a critical large-scale feature for extreme rainfall and flooding in central Arizona. Contrasting spatial rainfall organizations and storm environment under the four synoptic modes highlights the role of interactions among synoptic conditions, mesoscale processes, and complex terrains in determining space–time variability of convective activities and flash flood hazards in central Arizona. We characterize structure and evolution properties of flood-producing storms based on storm tracking algorithms and 3D radar reflectivity. Fast-moving storm elements can be important ingredients for flash floods in the arid/semiarid southwestern United States. Contrasting storm properties for cloudburst storms highlight the wide spectrum of convective intensities for extreme rain rates in the arid/semiarid southwestern United States and exhibit comparable vertical structures to their counterparts in the eastern United States.

scholarly journals PRINCIPAL CLIMATE INDICES FOR THE NORTH PACIFIC: NATURE AND HISTORY (A REVIEW)

2019 ◽  
Vol 197 ◽  
pp. 166-181 ◽  
Author(s):  
G. V. Khen ◽  
E. I. Ustinova ◽  
Yu. D. Sorokin
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Southern Oscillation ◽  
Physical Nature ◽  
Climate Indices ◽  
Air Masses ◽  
Climatic Indices ◽  
The North ◽  
Northern Pacific ◽  
The North Pacific

 Climatic indices reflecting the environmental conditions and patterns of their variability in the entire northern Pacific and in its local regions are overviewed. Their physical nature and mechanisms of the processes, their geography and methods of calculation are presented, with citing of the first descriptions. Among a variety of global and regional climatic indices concern ing the North Pacific, the following ones are described: the indices of Arctic Oscillation (AO), El Niño — Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Aleutian Low Pressure Index (ALPI), Siberian High Index (SHI), North Pacific Index (NPI), Pacific/North American (PNA) Index, and West Pacific Index (WP). AO is a large-scale index of atmospheric circulation reflecting the processes both in the troposphere and stratosphere, where «pumping» of air masses between the high and moderate latitudes occurs continuously. ENSO is also a large-scale index that reflects large-scale interactions in the fields of temperature, atmospheric pressure, wind, and cloudiness over the whole Pacific. Other indices are rather regional, since their influence does not extend far beyond the limits of the domains of their definition. Nevertheless, their role in environmental fluctuations in certain areas could be significant and their influence could be traced throughout the Northern Hemisphere.

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