scholarly journals CMIP5 Simulations of Low-Level Tropospheric Temperature and Moisture over the Tropical Americas

2013 ◽  
Vol 26 (17) ◽  
pp. 6257-6286 ◽  
Author(s):  
Leila M. V. Carvalho ◽  
Charles Jones
Keyword(s):  
Daily Precipitation ◽  
Monsoon Season ◽  
Coupled Model ◽  
Specific Humidity ◽  
Cmip5 Models ◽  
North American Monsoon ◽  
Tropospheric Temperature ◽  
The North ◽  
Decadal Variations ◽  
Monsoon System

Abstract Global warming has been linked to systematic changes in North and South America's climates and may severely impact the North American monsoon system (NAMS) and South American monsoon system (SAMS). This study examines interannual-to-decadal variations and changes in the low-troposphere (850 hPa) temperature (T850) and specific humidity (Q850) and relationships with daily precipitation over the tropical Americas using the NCEP–NCAR reanalysis, the Climate Forecast System Reanalysis (CFSR), and phase 5 of the Coupled Model Intercomparison Project (CMIP5) simulations for two scenarios: “historic” and high-emission representative concentration pathway 8.5 (RCP8.5). Trends in the magnitude and area of the 85th percentiles were distinctly examined over North America (NA) and South America (SA) during the peak of the respective monsoon season. The historic simulations (1951–2005) and the two reanalyses agree well and indicate that significant warming has occurred over tropical SA with a remarkable increase in the area and magnitude of the 85th percentile in the last decade (1996–2005). The RCP8.5 CMIP5 ensemble mean projects an increase in the T850 85th percentile of about 2.5°C (2.8°C) by 2050 and 4.8°C (5.5°C) over SA (NA) by 2095 relative to 1955. The area of SA (NA) with T850 ≥ the 85th percentile is projected to increase from ~10% (15%) in 1955 to ~58% (~33%) by 2050 and ~80% (~50%) by 2095. The respective increase in the 85th percentile of Q850 is about 3 g kg−1 over SAMS and NAMS by 2095. CMIP5 models project variable changes in daily precipitation over the tropical Americas. The most consistent is increased rainfall in the intertropical convergence zone in December–February (DJF) and June–August (JJA) and decreased precipitation over NAMS in JJA.

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 Future Changes and Controlling Factors of the Eight Regional Monsoons Projected by CMIP6 Models

2020 ◽  
Vol 33 (21) ◽  
pp. 9307-9326
Author(s):  
Chunhan Jin ◽  
Bin Wang ◽  
Jian Liu
Keyword(s):  
Monsoon Rainfall ◽  
Rainfall Variability ◽  
Coupled Model ◽  
Summer Rainfall ◽  
Winter Precipitation ◽  
Specific Humidity ◽  
North American Monsoon ◽  
Central Pacific ◽  
The North ◽  
Spread Analysis

AbstractAn accurate prediction of land monsoon precipitation (LMP) is critical for the sustainable future of the planet as it provides water resources for more than two-thirds of the global population. Here, we show that the ensemble mean of 24 CMIP6 (phase 6 of the Coupled Model Intercomparison Project) models projects that, under the Shared Socioeconomic Pathway 2–4.5 (SSP2–4.5) scenario, summer LMP will very likely increase in South Asia (~4.1% °C−1), likely increase in East Asia (~4.6% °C−1) and northern Africa (~2.9% °C−1), and likely decrease in North America (~−2.3% °C−1). The annual mean LMP in three Southern Hemisphere monsoon regions will likely remain unchanged due to significantly decreased winter precipitation. Regional mean LMP changes are dominated by the change in upward moisture transport with moderate contribution from evaporation and can be approximated by the changes of the product of the midtropospheric ascent and 850-hPa specific humidity. Greenhouse gas (GHG)-induced thermodynamic effects increase moisture content and stabilize the atmosphere, tending to offset each other. The spatially uniform increase of humidity cannot explain markedly different regional LMP changes. Intermodel spread analysis demonstrates that the GHG-induced circulation changes (dynamic effects) are primarily responsible for the regional differences. The GHGs induce a warm land–cool ocean pattern that strengthens the Asian monsoon, and a warm North Atlantic and Sahara that enhances the northern African monsoon, as well as an equatorial central Pacific warming that weakens the North American monsoon. CMIP6 models generally capture realistic monsoon rainfall climatology, but commonly overproduce summer rainfall variability. The models’ biases in projected regional SST and land–sea thermal contrast likely contribute to the models’ uncertainties in the projected monsoon rainfall changes.

scholarly journals On the competition among aerosol number, size and composition in predicting CCN variability: a multi-annual field study in an urbanized desert

2015 ◽  
Vol 15 (12) ◽  
pp. 6943-6958 ◽  
Author(s):  
E. Crosbie ◽  
J.-S. Youn ◽  
B. Balch ◽  
A. Wonaschütz ◽  
T. Shingler ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
North American ◽  
Monsoon Season ◽  
Aerosol Size Distribution ◽  
North American Monsoon ◽  
Aerosol Composition ◽  
Data Set ◽  
The North ◽  
Concentration Changes

Abstract. A 2-year data set of measured CCN (cloud condensation nuclei) concentrations at 0.2 % supersaturation is combined with aerosol size distribution and aerosol composition data to probe the effects of aerosol number concentrations, size distribution and composition on CCN patterns. Data were collected over a period of 2 years (2012–2014) in central Tucson, Arizona: a significant urban area surrounded by a sparsely populated desert. Average CCN concentrations are typically lowest in spring (233 cm−3), highest in winter (430 cm−3) and have a secondary peak during the North American monsoon season (July to September; 372 cm−3). There is significant variability outside of seasonal patterns, with extreme concentrations (1 and 99 % levels) ranging from 56 to 1945 cm−3 as measured during the winter, the season with highest variability. Modeled CCN concentrations based on fixed chemical composition achieve better closure in winter, with size and number alone able to predict 82 % of the variance in CCN concentration. Changes in aerosol chemical composition are typically aligned with changes in size and aerosol number, such that hygroscopicity can be parameterized even though it is still variable. In summer, models based on fixed chemical composition explain at best only 41 % (pre-monsoon) and 36 % (monsoon) of the variance. This is attributed to the effects of secondary organic aerosol (SOA) production, the competition between new particle formation and condensational growth, the complex interaction of meteorology, regional and local emissions and multi-phase chemistry during the North American monsoon. Chemical composition is found to be an important factor for improving predictability in spring and on longer timescales in winter. Parameterized models typically exhibit improved predictive skill when there are strong relationships between CCN concentrations and the prevailing meteorology and dominant aerosol physicochemical processes, suggesting that similar findings could be possible in other locations with comparable climates and geography.

Frequency Modes of Monsoon Precipitation in Arizona and New Mexico

2006 ◽  
Vol 134 (12) ◽  
pp. 3774-3781 ◽  
Author(s):  
Anne W. Nolin ◽  
Eileen A. Hall-McKim
Keyword(s):  
New Mexico ◽  
Wavelet Analysis ◽  
Monsoon Season ◽  
Intraseasonal Variability ◽  
Low Frequency ◽  
North American Monsoon ◽  
Monsoon Precipitation ◽  
Monsoon Period ◽  
The North ◽  
Spectral Analysis Method

Abstract The interannual and intraseasonal variability of the North American monsoon is of great interest because a large proportion of the annual precipitation for Arizona and New Mexico arrives during the summer monsoon. Forty-one years of daily monsoon season precipitation data for Arizona and New Mexico were studied using wavelet analysis. This time-localized spectral analysis method reveals that periodicities of less than 8 days are positively correlated with mean daily precipitation during the 1 July–15 September monsoon period. Roughly 17% of the years indicate no significant periodicity during the monsoon period for either region and are associated with low monsoon precipitation. High- and low-frequency modes explain an equivalent percentage of the variance in monsoon precipitation in both Arizona and New Mexico, and in many years concurrent multiple periodicities occur. Wavelet analysis was effective in identifying the contribution of high-frequency modes that had not been discerned in previous studies. These results suggest that precipitation processes during the monsoon season are modulated by phenomena operating at synoptic (2–8 days) and longer (>8 days) time scales and point to the need for further studies to better understand the associated atmospheric processes.

scholarly journals CMIP5 Projections of Arctic Amplification, of the North American/North Atlantic Circulation, and of Their Relationship

2015 ◽  
Vol 28 (13) ◽  
pp. 5254-5271 ◽  
Author(s):  
Elizabeth A. Barnes ◽  
Lorenzo M. Polvani
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Coupled Model ◽  
Arctic Region ◽  
The Arctic ◽  
Cmip5 Models ◽  
Arctic Amplification ◽  
Arctic Warming ◽  
The North ◽  
Sequence Of Events

Abstract Recent studies have hypothesized that Arctic amplification, the enhanced warming of the Arctic region compared to the rest of the globe, will cause changes in midlatitude weather over the twenty-first century. This study exploits the recently completed phase 5 of the Coupled Model Intercomparison Project (CMIP5) and examines 27 state-of-the-art climate models to determine if their projected changes in the midlatitude circulation are consistent with the hypothesized impact of Arctic amplification over North America and the North Atlantic. Under the largest future greenhouse forcing (RCP8.5), it is found that every model, in every season, exhibits Arctic amplification by 2100. At the same time, the projected circulation responses are either opposite in sign to those hypothesized or too widely spread among the models to discern any robust change. However, in a few seasons and for some of the circulation metrics examined, correlations are found between the model spread in Arctic amplification and the model spread in the projected circulation changes. Therefore, while the CMIP5 models offer some evidence that future Arctic warming may be able to modulate some aspects of the midlatitude circulation response in some seasons, the analysis herein leads to the conclusion that the net circulation response in the future is unlikely to be determined solely—or even primarily—by Arctic warming according to the sequence of events recently hypothesized.

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.

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