scholarly journals The Variabilities of Convective Precipitation and Large-scale Precipitation in Southern China under Global Warming

2021 ◽  
Author(s):  
han zhang ◽  
Junhu Zhao ◽  
Bicheng Huang ◽  
Naihui Zang ◽  
Jie Yang ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Large Scale ◽  
Southern China ◽  
Specific Humidity ◽  
Convective Precipitation ◽  
The Past ◽  
The North ◽  
Increasing Trends ◽  
Spatial And Temporal Characteristics ◽  
Linear Trends

Abstract In this paper, the spatial and temporal characteristics of convective precipitation (CP) and large-scale precipitation (LSP) in southern China during 1980-2020 are analyzed using monthly mean precipitation data from MERRA-2. In addition, the possible effects of relative humidity on CP and LSP are explored. The results indicate the following. (1) The LSP dominates the proportion of total precipitation (TP). Both LSP and CP are more prevalent in the south and less prevalent in the north, but there is a difference in the regions of their maximum centers. (2) Significant interannual and seasonal variations are observed in precipitation. TP and LSP tended to be higher than average after the 1990s, while for the CP, a negative trend has dominated the past years with considerable fluctuation. There are obvious increasing trends for TP and LSP, with area-averaged linear trends of 7.0 mm/year and 8.9 mm/year, respectively, while that of CP is -1.9 mm/year. The increasing trends of LSP are mainly contributed by the precipitation of summer and autumn. (3) The variations of LSP are affected by relative humidity in the troposphere, while CP is only influenced by the changes in relative humidity due to air temperature or specific humidity. The trend of relative humidity is -0.32%/decade, mainly due to rising temperature in the troposphere. (4) Changes in specific humidity caused by temperature or specific humidity alone act on large-scale precipitation through both interannual and interdecadal processes, causing large-scale precipitation to increase. And the convective precipitation is mainly affected by the interdecadal processes.

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 Global climatology and trends in convective environments from ERA5 and rawinsonde data

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateusz Taszarek ◽  
John T. Allen ◽  
Mattia Marchio ◽  
Harold E. Brooks
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Convective Precipitation ◽  
The Past ◽  
The Tropics ◽  
Rawinsonde Data

AbstractGlobally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

scholarly journals Anticorrelated observed and modeled trends in dissolved oceanic oxygen over the last 50 years

2012 ◽  
Vol 9 (4) ◽  
pp. 4595-4626 ◽  
Author(s):  
L. Stramma ◽  
A. Oschlies ◽  
S. Schmidtko
Keyword(s):  
Large Scale ◽  
Model Comparison ◽  
Numerical Models ◽  
Regional Patterns ◽  
The Past ◽  
Tropical Oceans ◽  
Model Configuration ◽  
Pattern Correlation ◽  
Increasing Trends ◽  
Global Mean

Abstract. Observations and model runs indicate trends in dissolved oxygen (DO) associated with current and ongoing global warming. However, a large-scale observation-to-model comparison has been missing and is presented here. This study presents a first global compilation of DO measurements covering the last 50 years. It shows declining upper-ocean DO levels in many regions, especially the tropical oceans, whereas areas with increasing trends are found in the subtropics and in some subpolar regions. For the Atlantic Ocean south of 20° N, the DO history could even be extended back to about 70 years, showing decreasing DO in the subtropical South Atlantic. The global mean DO trend between 50° S and 50° N at 300 dbar for the period 1960 to 2010 is −0.063 μmol kg−1 yr−1. Results of a numerical biogeochemical Earth system model reveal that the magnitude of the observed change is consistent with CO2-induced climate change. However, the correlation between simulated and observed patterns of past DO change is negative, indicating that the model does not correctly reproduce the processes responsible for observed regional oxygen changes in the past 50 years. A negative pattern correlation is also obtained for model configurations with particularly low and particularly high diapycnal mixing, for a configuration that assumes a CO2-induced enhancement of the C:N ratios of exported organic matter and irrespective of whether climatological or realistic winds from reanalysis products are used to force the model. Depending on the model configuration the 300 dbar DO trend between 50° S and 50° N is −0.026 to −0.046 μmol kg−1 yr−1. Although numerical models reproduce the overall sign and, to some extent, magnitude of observed ocean deoxygenation, this degree of realism does not necessarily apply to simulated regional patterns and the representation of processes involved in their generation. Further analysis of the processes that can explain the discrepancies between observed and modeled DO trends is required to better understand the climate sensitivity of oceanic oxygen fields and predict potential DO changes in the future.

scholarly journals Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

2019 ◽  
Vol 19 (11) ◽  
pp. 7487-7506
Author(s):  
Keun-Ok Lee ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Cyrille Flamant ◽  
Jean-Lionel Lacour ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Water Isotopes ◽  
Precipitation Event ◽  
Stable Water Isotopes ◽  
Heavy Precipitation Event ◽  
The North ◽  
Upper Level

Abstract. The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMOiso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the north-western Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ18O ≤-25 ‰, water vapour mixing ratio q≤2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ18O ≥-14 ‰) and moistened (q≥8 g kg−1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over SI, producing a large amount of convective precipitation in SI. Most of the moisture processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 h before P1 over SI. A period of 4 h later, during the second precipitation phase P2, the air parcels arriving over SI mainly originate from north Africa. The strong cyclonic flow around the eastward-moving upper-level trough induces the advection of a SWI-enriched African moisture plume towards SI and leads to large-scale uplift of the warm air mass along the cold front. This lifts moist and SWI-enriched air (median δ18O ≥-16 ‰, median q≥6 g kg−1) and leads to gradual rain out of the air parcels over Italy. Large-scale ascent in the warm sector ahead of the cold front takes place during the 72 h preceding P2 in SI. This work demonstrates how stable water isotopes can yield additional insights into the variety of thermodynamic mechanisms occurring at the mesoscale and synoptic scale during the formation of a HPE.

Cameroon’s anglophone resistance will endure

2017 ◽  
Keyword(s):  
Government Spending ◽  
Large Scale ◽  
Linguistic Minority ◽  
False Information ◽  
Content Type ◽  
Lake Chad ◽  
High Profile ◽  
The Past ◽  
The North ◽  
Ghost Town

Significance They face trial for “complicity in acts of terrorism, insurrection, rebellion and the propagation of false information”. Anglophone Cameroonians in the Northwest and Southwest regions have been staging strikes and protests against discrimination as a linguistic minority in the past months. This prompted a government shutdown of the internet in January, which was restored in April. Although large-scale protests have stopped, many schools remain closed, the larger cities in the region continue weekly ‘ghost town’ strikes and several high-profile protesters are still under arrest. Impacts Pre-election government spending will likely increase, specifically targeted at the Northwest and Southwest regions. Attacks in the north by Boko Haram will persist and pose a growing threat to Lake Chad counterterrorism efforts. Diplomatic tensions could grow between Cameroon and Nigeria over the resettlement of refugees.

Trend of Surface Air Temperature in Eastern China and Associated Large-Scale Climate Variability over the Last 100 Years

2014 ◽  
Vol 27 (12) ◽  
pp. 4693-4703 ◽  
Author(s):  
Ping Zhao ◽  
Phil Jones ◽  
Lijuan Cao ◽  
Zhongwei Yan ◽  
Shuyao Zha ◽  
...  
Keyword(s):  
Air Temperature ◽  
Large Scale ◽  
Eastern China ◽  
Surface Air Temperature ◽  
Tropical Indian Ocean ◽  
Population Data ◽  
Warming Trend ◽  
Climate Indices ◽  
The Past ◽  
Linear Trends

Abstract Using the reconstructed continuous and homogenized surface air temperature (SAT) series for 16 cities across eastern China (where the greatest industrial developments in China have taken place) back to the nineteenth century, the authors examine linear trends of SAT. The regional-mean SAT over eastern China shows a warming trend of 1.52°C (100 yr)−1 during 1909–2010. It mainly occurred in the past 4 decades and this agrees well with the variability in another SAT series developed from a much denser station network (over 400 sites) across this part of China since 1951. This study collects population data for 245 sites (from these 400+ locations) and split these into five equally sized groups based on population size. Comparison of these five groups across different durations from 30 to 60 yr in length indicates that differences in population only account for between 9% and 24% of the warming since 1951. To show that a larger urbanization impact is very unlikely, the study additionally determines how much can be explained by some large-scale climate indices. Anomalies of large-scale climate indices such as the tropical Indian Ocean SST and the Siberian atmospheric circulation systems account for at least 80% of the total warming trends.

The impact of large-scale circulation on daily fine particulate matter (PM2.5) in major populated regions of China during winter 

2021 ◽  
Author(s):  
Zixuan Jia ◽  
Ruth Doherty ◽  
Carlos Ordóñez ◽  
Chaofan Li ◽  
Oliver Wild
Keyword(s):  
Particulate Matter ◽  
Relative Humidity ◽  
Large Scale ◽  
Southern China ◽  
East Asian ◽  
River Delta ◽  
Large Scale Circulation ◽  
East Asian Trough ◽  
Siberian High ◽  
Pollution Episodes

<p>With rapid economic growth and urbanization, air pollution episodes with high levels of particulate matter (PM<sub>2.5</sub>) have become common in China. While emissions of pollutant precursors are important, meteorology also plays a major role in pollution episodes, especially in winter. We examine the influence of the dominant large-scale circulation and the key regional meteorological features on PM<sub>2.5</sub> over three major regions of China: Beijing–Tianjin–Hebei (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD). The East Asian winter monsoon (EAWM) is primarily studied, including some of its main large-scale components such as the East Asian trough and the Siberian high, as it influences PM<sub>2.5 </sub>differently in different parts of China. In the BTH region, the shallow East Asian trough curbs the invasion of northerly cold and dry air from the Siberian high which induces high relative humidity and heavy pollution, possibly via relative humidity-promoted aerosol formation and growth. A weak southerly wind in Eastern and Southern China associated with a weakened Siberian high suppresses horizontal dispersion, contributing to pollution accumulation over YRD. In addition, the El Niño-Southern Oscillation (ENSO) as the dominant mode of global ocean-atmosphere interaction has a substantial modulation on precipitation over southern China. In the PRD, weak southerly winds and precipitation deficits over southern China are conducive to atmospheric pollution possibly via reduced wet deposition. Furthermore, we construct new circulation-based indices based on the dominant large-scale circulation: a 500 hPa geopotential height-based index for BTH, a sea level pressure-based index for YRD and an 850 hPa meridional wind-based index for PRD. These three indices can effectively distinguish different levels of pollution over BTH, YRD and PRD, respectively. We also show how additional regional meteorological variables can improve the prediction of regional PM<sub>2.5</sub> concentrations for these three regions. These results are beneficial to understanding and forecasting the occurrence of severely polluted days for BTH, YRD and PRD from a large-scale perspective.</p>

Precipitation–Radiation–Circulation Feedback Processes Associated with Structural Changes of the ITCZ in a Warming Climate during 1980–2014: An Observational Portrayal

2020 ◽  
Vol 33 (20) ◽  
pp. 8737-8749 ◽  
Author(s):  
William K. M. Lau ◽  
Weichen Tao
Keyword(s):  
Relative Humidity ◽  
Large Scale ◽  
Structural Changes ◽  
Climate Model ◽  
Longwave Radiation ◽  
Hadley Circulation ◽  
Specific Humidity ◽  
Necessary Condition ◽  
Multiple Sources

AbstractIn this study, long-term structural changes in the intertropical convergence zone (ITCZ) and associated precipitation–radiation–circulation feedback processes are examined using multiple sources of reanalysis data for temperature, winds, moisture, and observed precipitation and outgoing longwave radiation (OLR) during 1980–2014. Consistent with CMIP5 climate model projections of the “deep tropical squeeze” under greenhouse warming, this period witnessed a warming and wetting (increased specific humidity) global trend, characterized by a narrowing of the ITCZ core with increased precipitation, coupled to widespread tropospheric drying (deficient relative humidity), increased OLR in the subtropics and midlatitudes, a widening of the descending branches of the Hadley circulation, and a poleward shift of the jet streams in both hemispheres. The widespread tropospheric drying stems from 1) a faster rate of increased saturated water vapor with warming, relative to the increase in ambient moisture due to convective and large-scale transport, and 2) enhanced anomalous subsidence, and low-level moisture divergence in the subtropics and midlatitudes. The long-term trend in enhanced precipitation (latent heating) in the ITCZ core region is strongly coupled to increasing OLR (radiative cooling to space) in the expanding dry zones, particularly over land regions in the subtropics and midlatitudes, arguably as a necessary condition for global thermodynamic energy balance. Analyses of the trend patterns in vertical profiles of p velocity, temperature, and relative humidity with respect to ITCZ precipitation rate and OLR reveal that the contrast between the wet and dry regions in the troposphere has been increasing globally, with the ITCZ core getting wetter and contracting, while the marginal convective and dry zones are getting drier and expanding.

scholarly journals Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

2011 ◽  
Vol 11 (1) ◽  
pp. 345-361 ◽  
Author(s):  
C.-Y. Lin ◽  
H.-m. Hsu ◽  
Y.-F. Sheng ◽  
C.-H. Kuo ◽  
Y.-A. Liou
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Specific Humidity ◽  
Mountain Range ◽  
Typhoon Morakot ◽  
Data Set ◽  
The North ◽  
Wave Trains ◽  
Convective Cells ◽  
Mesoscale Processes

Abstract. Within 100 h, a record-breaking rainfall, 2855 mm, was brought to Taiwan by typhoon Morakot in August 2009 resulting in devastating landslides and casualties. Analyses and simulations show that under favorable large-scale situations, this unprecedented precipitation was caused first by the convergence of the southerly component of the pre-existing strong southwesterly monsoonal flow and the northerly component of the typhoon circulation. Then the westerly component of southwesterly flow pushed the highly moist air (mean specific humidity >16 g/kg between 950 and 700 hPa from NCEP GFS data set) eastward against the Central Mountain Range, and forced it to lift in the preferred area. From the fine-scale numerical simulation, not only did the convergence itself provide the source of the heavy rainfall when it interacted with the topography, but also convective cells existed within the typhoon's main rainband. The convective cells were in the form of small rainbands perpendicular to the main one, and propagated as wave trains downwind. As the main rainband moved northward and reached the southern CMR, convective cells inside the narrow convergence zone to the south and those to the north as wave trains, both rained heavily as they were lifted by the west-facing mountain slopes. Those mesoscale processes were responsible for the unprecedented heavy rainfall total that accompanied this typhoon.

scholarly journals Stationary Eddies and the Zonal Asymmetry of Net Precipitation and Ocean Freshwater Forcing

2015 ◽  
Vol 28 (13) ◽  
pp. 5115-5133 ◽  
Author(s):  
Robert C. Wills ◽  
Tapio Schneider
Keyword(s):  
Spatial Variability ◽  
Large Scale ◽  
Vertical Motion ◽  
Sea Surface Salinity ◽  
Specific Humidity ◽  
Ekman Pumping ◽  
Surface Salinity ◽  
The North ◽  
Freshwater Forcing ◽  
The Pacific

Abstract Transport of water vapor in the atmosphere generates substantial spatial variability of net precipitation (precipitation minus evaporation). Over half of the total spatial variability in annual-mean net precipitation is accounted for by deviations from the zonal mean. Over land, these regional differences determine differences in surface water availability. Over oceans, they account, for example, for the Pacific–Atlantic difference in sea surface salinity, with implications for the deep overturning circulation. This study analyzes the atmospheric water budget in reanalyses from ERA-Interim and MERRA, to investigate which physical balances lead to zonal variation in net precipitation. It is found that the leading-order contribution is zonal variation in stationary-eddy vertical motion. Transient eddies modify the pattern of zonally anomalous net precipitation by moving moisture from the subtropical and tropical oceans onto land and poleward across the Northern Hemisphere storm tracks. Zonal variation in specific humidity and stationary-eddy horizontal advection play a secondary role. The dynamics leading to net precipitation via vertical motion in stationary eddies can be understood from a lower-tropospheric vorticity budget. The large-scale variations of vertical motion are primarily described by Sverdrup balance and Ekman pumping, with some modification by transient eddies. These results suggest that it is important to understand changes in stationary eddies and their influence on the zonal variation of transient eddy fluxes, in order to understand regional changes in net precipitation. They highlight the relative importance of different atmospheric mechanisms for the freshwater forcing of the North Pacific and North Atlantic.

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