scholarly journals Warm Season Rainfall Variability over the U.S. Great Plains in Observations, NCEP and ERA-40 Reanalyses, and NCAR and NASA Atmospheric Model Simulations

2005 ◽  
Vol 18 (11) ◽  
pp. 1808-1830 ◽  
Author(s):  
Alfredo Ruiz-Barradas ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Rainfall Variability ◽  
Warm Season ◽  
Moisture Flux ◽  
Atmospheric Model ◽  
Precipitation Variability ◽  
Reanalysis Data ◽  
Ncep Reanalysis ◽  
Model Simulations ◽  
Precipitation Estimates

Abstract Interannual variability of Great Plains precipitation in the warm season months is analyzed using gridded observations, satellite-based precipitation estimates, NCEP reanalysis data and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data, and the half-century-long NCAR Community Atmosphere Model (CAM3.0, version 3.0) and the National Aeronautics and Space Administration (NASA) Seasonal-to-Intraseasonal Prediction Project (NSIPP) atmospheric model simulations. Regional hydroclimate is the focus because of its immense societal impact and because the involved variability mechanisms are not well understood. The Great Plains precipitation variability is represented rather differently, and only quasi realistically, in the reanalyses. NCEP has larger amplitude but less traction with observations in comparison with ERA-40. Model simulations exhibit more realistic amplitudes, which are between those of NCEP and ERA-40. The simulated variability is however uncorrelated with observations in both models, with monthly correlations smaller than 0.10 in all cases. An assessment of the regional atmosphere water balance is revealing: Stationary moisture flux convergence accounts for most of the Great Plains variability in ERA-40, but not in the NCEP reanalysis and model simulations; convergent fluxes generate less than half of the precipitation in the latter, while local evaporation does the rest in models. Phenomenal evaporation in the models—up to 4 times larger than the highest observationally constrained estimate (NCEP’s)—provides the bulk of the moisture for Great Plains precipitation variability; thus, precipitation recycling is very efficient in both models, perhaps too efficient. Remote water sources contribute substantially to Great Plains hydroclimate variability in nature via fluxes. Getting the interaction pathways right is presently challenging for the models.

scholarly journals Warm Season Variations in the Low-Level Circulation and Precipitation over the Central United States in Observations, AMIP Simulations, and Idealized SST Experiments

2009 ◽  
Vol 22 (20) ◽  
pp. 5401-5420 ◽  
Author(s):  
Scott J. Weaver ◽  
Siegfried Schubert ◽  
Hailan Wang
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Climate Model ◽  
Warm Season ◽  
Atmospheric Model ◽  
Warm Pool ◽  
Precipitation Variability ◽  
Western Hemisphere ◽  
Low Level ◽  
Sst Variability

Abstract Sea surface temperature (SST) linkages to central U.S. low-level circulation and precipitation variability are investigated from the perspective of the Great Plains low-level jet (GPLLJ) and recurring modes of SST variability. The observed and simulated links are first examined via GPLLJ index regressions to precipitation, SST, and large-scale circulation fields in the NCEP–NCAR and North American Regional Reanalysis (NARR) reanalyses, and NASA’s Seasonal-to-Interannual Prediction Project (NSIPP1) and Community Climate Model, version 3 (CCM3) ensemble mean Atmospheric Model Intercomparison Project (AMIP) simulations for the 1949–2002 (1979–2002 for NARR) period. Characteristics of the low-level circulation and its related precipitation are further examined in the U.S. Climate Variability and Predictability (CLIVAR) Drought Working Group idealized climate model simulations (NSIPP1 and CCM3) forced with varying polarities of recurring modes of SST variability. It is found that the observed and simulated correlations of the GPLLJ index to Atlantic and Pacific SST, large-scale atmospheric circulation, and Great Plains precipitation variability for 1949–2002 are robust during the July–September (JAS) season and show connections to a distinct global-scale SST variability pattern, one similar to that used in forcing the NSIPP1 and CCM3 idealized simulations, and a subtropical Atlantic-based sea level pressure (SLP) anomaly with a maximum over the Gulf of Mexico. The idealized simulations demonstrate that a warm Pacific and/or a cold Atlantic are influential over regional hydroclimate features including the monthly preference for maximum GPLLJ and precipitation in the seasonal cycle. Furthermore, it appears that the regional expression of globally derived SST variability is important for generating an anomalous atmospheric low-level response of consequence to the GPLLJ, especially when the SST anomaly is positioned over a regional maximum in climatological SST, and in this case the Western Hemisphere warm pool.

Dryness over the U.S. Southwest, a Springboard for Cold Season Pacific SST to Influence Warm Season Drought over the U.S. Great Plains

2021 ◽  
Vol 22 (1) ◽  
pp. 63-76
Author(s):  
Yizhou Zhuang ◽  
Amir Erfanian ◽  
Rong Fu
Keyword(s):  
Great Plains ◽  
Land Surface ◽  
Rainfall Variability ◽  
Warm Season ◽  
Summer Precipitation ◽  
Cold Season ◽  
Early Summer ◽  
Moisture Condition ◽  
Moisture Advection ◽  
The U.S

AbstractAlthough the influence of sea surface temperature (SST) forcing and large-scale teleconnection on summer droughts over the U.S. Great Plains has been suggested for decades, the underlying mechanisms are still not fully understood. Here we show a significant correlation between low-level moisture condition over the U.S. Southwest in spring and rainfall variability over the Great Plains in summer. Such a connection is due to the strong influence of the Southwest dryness on the zonal moisture advection to the Great Plains from spring to summer. This advection is an important contributor for the moisture deficit during spring to early summer, and so can initiate warm season drought over the Great Plains. In other words, the well-documented influence of cold season Pacific SST on the Southwest rainfall in spring, and the influence of the latter on the zonal moisture advection to the Great Plains from spring to summer, allows the Pacific climate variability in winter and spring to explain over 35% of the variance of the summer precipitation over the Great Plains, more than that can be explained by the previous documented west Pacific–North America (WPNA) teleconnection forced by tropical Pacific SST in early summer. Thus, this remote land surface feedback due to the Southwest dryness can potentially improve the predictability of summer precipitation and drought onsets over the Great Plains.

scholarly journals Contributions of Different Combinations of the IPO and AMO to Recent Changes in Winter East Asian Jets

2019 ◽  
Vol 32 (5) ◽  
pp. 1607-1626 ◽  
Author(s):  
Danqing Huang ◽  
Aiguo Dai ◽  
Ben Yang ◽  
Peiwen Yan ◽  
Jian Zhu ◽  
...  
Keyword(s):  
Potential Energy ◽  
East Asian ◽  
Atlantic Multidecadal Oscillation ◽  
Atmospheric Model ◽  
Polar Front ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Model Simulations ◽  
Available Potential Energy ◽  
Two Jets

Abstract Recent concurrent shifts of the East Asian polar-front jet (EAPJ) and the East Asian subtropical jet (EASJ) in the boreal winter have raised concerns, since they could result in severe weather events over East Asia. However, the possible mechanisms are not fully understood. In this study, the roles of the interdecadal Pacific oscillation (IPO) and the Atlantic multidecadal oscillation (AMO) are investigated by analyzing reanalysis data and model simulations. Results show that combinations of opposite phases of the IPO and AMO can result in significant shifts of the two jets during 1920–2014. This relationship is particularly evident during 1999–2014 and 1979–98 in the reanalysis data. A combination of a negative phase of the IPO (−IPO) and a positive phase of the AMO (+AMO) since the late 1990s has enhanced the meridional temperature gradient and the Eady growth rate and thus westerlies over the region between the two jets, but weakened them to the south and north of the region, thereby contributing to the equatorward and poleward shifts of the EAPJ and EASJ, respectively. Atmospheric model simulations are further used to investigate the relative contribution of −IPO and +AMO to the jet shifts. The model simulations show that the combination of −IPO and +AMO favors the recent jet changes more than the individual −IPO or +AMO. Under a concurrent −IPO and +AMO, the meridional eddy transport of zonal momentum and sensitive heat strengthens, and more mean available potential energy converts to the eddy available potential energy over the region between the two jets, which enhances westerly winds there.

scholarly journals An Investigation of Warm-Season Spatial Rainfall Variability in Oklahoma City: Possible Linkages to Urbanization and Prevailing Wind

2009 ◽  
Vol 48 (2) ◽  
pp. 251-269 ◽  
Author(s):  
Lauren M. Hand ◽  
J. Marshall Shepherd
Keyword(s):  
Rainfall Variability ◽  
Warm Season ◽  
Daily Rainfall ◽  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Rainfall Anomaly ◽  
Reanalysis Data ◽  
Oklahoma City ◽  
Prevailing Wind ◽  
Rainfall Estimates

Abstract This study used 9 yr (1998–2006) of warm-season (June–September) mean daily cumulative rainfall data from both the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis and rain gauge stations to examine spatial variability in warm-season rainfall events around Oklahoma City (OKC). It was hypothesized that with warm-season rainfall variability, under weakly forced conditions, a rainfall anomaly would be present in climatological downwind areas of OKC. Results from both satellite and gauge-based analyses revealed that the north-northeastern (NNE) regions of the metropolitan OKC area were statistically wetter than other regions. Climatological sounding and reanalysis data revealed that, on average, the NNE area of OKC was the climatologically downwind region, confirming that precipitation modification by the urban environment may be more dominant than agricultural/topographic influences on weakly forced days. The study also established that satellite precipitation estimates capture spatial rainfall variability as well as traditional ground-based resources do. TRMM products slightly underestimate the precipitation recorded by gauges, but the correlation R improves dramatically when the analysis is restricted to mean daily rainfall estimates from OKC urban grid cells containing multiple gauge stations (R2 = 0.878). It was also quantitatively confirmed, using a relatively new concentration factor analysis, that prevailing wind–rainfall yields were consistent with the overall framework of an urban rainfall effect. Overall, the study establishes a prototype method for utilizing satellite-based rainfall estimates to examine rainfall modification by urbanization on global scales and in parts of the world that are not well instrumented with rain gauge or radar networks.

Seasonal Hydroclimate Variability over North America in Global and Regional Reanalyses and AMIP Simulations: Varied Representation

2006 ◽  
Vol 19 (5) ◽  
pp. 815-837 ◽  
Author(s):  
Sumant Nigam ◽  
Alfredo Ruiz-Barradas
Keyword(s):  
Great Plains ◽  
North American ◽  
Climate Models ◽  
Gulf Coast ◽  
Surface Air Temperature ◽  
Moisture Flux ◽  
Atmospheric Model ◽  
Eastern United States ◽  
Hydroclimate Variability ◽  
Regional Reanalysis

Abstract The monotony of seasonal variability is often compensated by the complexity of its spatial structure—the case in North American hydroclimate. The structure of hydroclimate variability is analyzed to provide insights into the functioning of the climate system and climate models. The consistency of hydroclimate representation in two global [40-yr ECMWF Re-Analysis (ERA-40) and NCEP] and one regional [North American Regional Reanalysis (NARR)] reanalysis is examined first, from analysis of precipitation, evaporation, surface air temperature (SAT), and moisture flux distributions. The intercomparisons benchmark the recently released NARR data and provide context for evaluation of the simulation potential of two state-of-the-art atmospheric models [NCAR's Community Atmospheric Model (CAM3.0) and NASA's Seasonal-to-Interannual Prediction Project (NSIPP) atmospheric model]. Intercomparisons paint a gloomy picture: great divergence in global reanalysis representations of precipitation, with the eastern United States being drier in ERA-40 and wetter in NCEP in the annual mean by up to a third in each case; model averages are like ERA-40. The annual means, in fact, mask even larger but offsetting seasonal departures. Analysis of moisture transport shows winter fluxes to be more consistently represented. Summer flux convergence over the Gulf Coast and Great Plains, however, differs considerably between global and regional reanalyses. Flux distributions help in understanding the choice of rainy season, especially the winter one in the Pacific Northwest; stationary fluxes are key. Land–ocean competition for convection is too intense in the models—so much so that the oceanic ITCZ in July is southward of its winter position in the both simulations! The overresponsiveness of land is also manifest in SAT; the winter-to-summer change over the Great Plains is 5–9 K larger than in observations, with implications for modeling of climate sensitivity. The nature of atmospheric water balance over the Great Plains is probed, despite unbalanced moisture budgets in reanalyses and model simulations. The imbalance is smaller in NARR but still unacceptably large, resulting from excessive evaporation in spring and summer. Adjusting evaporation during precipitation assimilation could lead to a more balanced budget. Global and regional reanalysis will remain of limited use for hydroclimate studies until they comply with the operative water and energy balance constraints.

scholarly journals Retrieval of Layer Averaged Relative Humidity Profiles from MHS Observations over Tropical Region

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
R. K. Gangwar ◽  
B. S. Gohil ◽  
A. K. Mathur
Keyword(s):  
Relative Humidity ◽  
Radiative Transfer ◽  
Reanalysis Data ◽  
Tropical Region ◽  
Atmospheric Layer ◽  
Ncep Reanalysis ◽  
Microwave Humidity Sounder ◽  
Using Data ◽  
Profile Errors ◽  
Humidity Profiles

The present paper deals with the retrieval of the atmospheric layer averaged relative humidity profiles using data from the Microwave Humidity Sounder (MHS) onboard the MetOp satellite. The retrieval has been innovatively performed by firstly retrieving humidity for pairs of thick overlapping layers (TOLs) used subsequently to derive humidity for associated thin isolated layer (TIL). A water vapour dependent (WVD) algorithm has been developed and applied to infer the humidity of TOLs. Thus, the retrieved profiles have been finally compared with standard algorithm (NORM). These algorithms have been developed based on radiative transfer simulations and study of sensitivities of MHS channels on humidity of various types of layers (TOL, TIL). The algorithm has been tested with MHS data and validated using concurrent radiosonde as well as NCEP reanalysis data indicating profile errors of ~15% and ~19%, respectively.

scholarly journals The Role of Mesoscale Convective Complexes in Southern Africa Summer Rainfall

2013 ◽  
Vol 26 (5) ◽  
pp. 1654-1668 ◽  
Author(s):  
R. C. Blamey ◽  
C. J. C. Reason
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
Rainfall Variability ◽  
Warm Season ◽  
Tropical Rainfall Measuring Mission ◽  
Summer Rainfall ◽  
Spatial And Temporal Variability ◽  
Eastern Region ◽  
Southwest Indian Ocean ◽  
Mesoscale Convective

Abstract A combination of numerous factors, including geographic position, regional orography, and local sea surface temperatures, means that subtropical southern Africa experiences considerable spatial and temporal variability in rainfall and is prone to both frequent flooding and drought events. One system that may contribute to rainfall variability in the region is the mesoscale convective complex (MCC). In this study, Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) data is used to document the precipitation produced by MCCs over southern Africa for the 1998–2006 period. Most of the rainfall associated with MCCs is found to occur over central Mozambique, extending southward to eastern South Africa. High precipitation totals associated with these systems also occur over the neighboring southwest Indian Ocean, particularly off the northeast coast of South Africa. MCCs are found to contribute up to 20% of the total summer rainfall (November–March) in parts of the eastern region of southern Africa. If the month of March is excluded from the analysis, then the contribution increases up to 24%. In general, the MCC summer rainfall contribution for most of the eastern region is approximately between 8% and 16%. Over the western interior and Botswana and Namibia, the MCC contribution is much less (<6%). It is also evident that there is considerable interannual variability associated with the contribution that these systems make to the total warm season rainfall.

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