scholarly journals Long-Lived Mesoconvective Vortices and Their Environment. Part I: Observations from the Central United States during the 1998 Warm Season

2000 ◽  
Vol 128 (10) ◽  
pp. 3376-3395 ◽  
Author(s):  
S. B. Trier ◽  
C. A. Davis ◽  
J. D. Tuttle
Keyword(s):  
United States ◽  
Warm Season ◽  
Central United States

NAM Model Forecasts of Warm-Season Quasi-Stationary Frontal Environments in the Central United States

2010 ◽  
Vol 25 (4) ◽  
pp. 1281-1292 ◽  
Author(s):  
Shih-Yu Wang ◽  
Adam J. Clark
Keyword(s):  
United States ◽  
Mesoscale Model ◽  
Convective Available Potential Energy ◽  
Warm Season ◽  
Correlation Coefficients ◽  
Precipitable Water ◽  
Wind Fields ◽  
Vapor Flux ◽  
Convective Systems ◽  
Central United States

Abstract Using a composite procedure, North American Mesoscale Model (NAM) forecast and observed environments associated with zonally oriented, quasi-stationary surface fronts for 64 cases during July–August 2006–08 were examined for a large region encompassing the central United States. NAM adequately simulated the general synoptic features associated with the frontal environments (e.g., patterns in the low-level wind fields) as well as the positions of the fronts. However, kinematic fields important to frontogenesis such as horizontal deformation and convergence were overpredicted. Surface-based convective available potential energy (CAPE) and precipitable water were also overpredicted, which was likely related to the overprediction of the kinematic fields through convergence of water vapor flux. In addition, a spurious coherence between forecast deformation and precipitation was found using spatial correlation coefficients. Composite precipitation forecasts featured a broad area of rainfall stretched parallel to the composite front, whereas the composite observed precipitation covered a smaller area and had a WNW–ESE orientation relative to the front, consistent with mesoscale convective systems (MCSs) propagating at a slight right angle relative to the thermal gradient. Thus, deficiencies in the NAM precipitation forecasts may at least partially result from the inability to depict MCSs properly. It was observed that errors in the precipitation forecasts appeared to lag those of the kinematic fields, and so it seems likely that deficiencies in the precipitation forecasts are related to the overprediction of the kinematic fields such as deformation. However, no attempts were made to establish whether the overpredicted kinematic fields actually contributed to the errors in the precipitation forecasts or whether the overpredicted kinematic fields were simply an artifact of the precipitation errors. Regardless of the relationship between such errors, recognition of typical warm-season environments associated with these errors should be useful to operational forecasters.

scholarly journals A Dual-Polarization Radar Synthetic QPE for Operations

2020 ◽  
Vol 21 (11) ◽  
pp. 2507-2521 ◽  
Author(s):  
Jian Zhang ◽  
Lin Tang ◽  
Stephen Cocks ◽  
Pengfei Zhang ◽  
Alexander Ryzhkov ◽  
...  
Keyword(s):  
United States ◽  
Scattered Light ◽  
Warm Season ◽  
Dual Polarization ◽  
Specific Attenuation ◽  
Central United States ◽  
Precipitation Estimation ◽  
Systematic Biases ◽  
Differential Reflectivity ◽  
Light Precipitation

AbstractA new dual-polarization (DP) radar synthetic quantitative precipitation estimation (QPE) product was developed using a combination of specific attenuation A, specific differential phase KDP, and reflectivity Z to calculate the precipitation rate R. Specific attenuation has advantages of being insensitive to systematic biases in Z and differential reflectivity ZDR due to partial beam blockage, attenuation, and calibration while more linearly related to R than other radar variables. However, the R(A) relationship is not applicable in areas containing ice. Therefore, the new DP QPE applies R(A) in areas where radar is observing pure rain, R(KDP) in regions potentially containing hail, and R(Z) elsewhere. Further, an evaporation correction was applied to minimize false light precipitation related to virga. The new DP QPE was evaluated in real time over the conterminous United States and showed significant improvements over previous radar QPE techniques that were based solely on R(Z) relationships. The improvements included reduced dry biases in heavy to extreme precipitation during the warm season. The new DP QPE also reduced errors and spatial discontinuities in regions impacted by partial beam blockage. Further, the new DP QPE reduced wet bias for scattered light precipitation in the southwest and north central United States where there is significant boundary layer evaporation.

Understanding the Distinct Impacts of MCS and Non-MCS Rainfall on the Surface Water Balance in the Central United States Using a Numerical Water-Tagging Technique

2020 ◽  
Vol 21 (10) ◽  
pp. 2343-2357
Author(s):  
Huancui Hu ◽  
L. Ruby Leung ◽  
Zhe Feng
Keyword(s):  
United States ◽  
Soil Moisture ◽  
Surface Water ◽  
Water Balance ◽  
Surface Runoff ◽  
Land Surface ◽  
Warm Season ◽  
Surface Model ◽  
Central United States ◽  
Infiltration Excess

ABSTRACTWarm-season rainfall associated with mesoscale convective systems (MCSs) in the central United States is characterized by higher intensity and nocturnal timing compared to rainfall from non-MCS systems, suggesting their potentially different footprints on the land surface. To differentiate the impacts of MCS and non-MCS rainfall on the surface water balance, a water tracer tool embedded in the Noah land surface model with multiparameterization options (WT-Noah-MP) is used to numerically “tag” water from MCS and non-MCS rainfall separately during April–August (1997–2018) and track their transit in the terrestrial system. From the water-tagging results, over 50% of warm-season rainfall leaves the surface–subsurface system through evapotranspiration by the end of August, but non-MCS rainfall contributes a larger fraction. However, MCS rainfall plays a more important role in generating surface runoff. These differences are mostly attributed to the rainfall intensity differences. The higher-intensity MCS rainfall tends to produce more surface runoff through infiltration excess flow and drives a deeper penetration of the rainwater into the soil. Over 70% of the top 10th percentile runoff is contributed by MCS rainfall, demonstrating its important contribution to local flooding. In contrast, lower-intensity non-MCS rainfall resides mostly in the top layer and contributes more to evapotranspiration through soil evaporation. Diurnal timing of rainfall has negligible effects on the flux partitioning for both MCS and non-MCS rainfall. Differences in soil moisture profiles for MCS and non-MCS rainfall and the resultant evapotranspiration suggest differences in their roles in soil moisture–precipitation feedbacks and ecohydrology.

scholarly journals Organization of Flash-Flood-Producing Precipitation in the Northeast United States

2012 ◽  
Vol 27 (2) ◽  
pp. 345-361 ◽  
Author(s):  
Stephen M. Jessup ◽  
Stephen J. Colucci
Keyword(s):  
United States ◽  
Flash Flood ◽  
Warm Season ◽  
Heavy Precipitation ◽  
Flash Flooding ◽  
Radar Signature ◽  
Long Duration ◽  
Central United States ◽  
Linear Types ◽  
Precipitation Estimates

Abstract Heavy precipitation and flash flooding have been extensively studied in the central United States, but less so in the Northeast. This study examines 187 warm-season flash flood events identified in Storm Data to better understand the structure of the precipitation systems that cause flash flooding in the Northeast. Based on the organization and movement of these systems on radar, the events are classified into one of four categories—back-building, linear, multiple, and other/size—and then further classified into subtypes for each category. Eight of these subtypes were not previously recognized in the literature. The back-building events were the most common, followed by the multiple, other/size, and linear types. The linear event types appear to produce flash flooding less commonly in the Northeast than in other regions. In general, the subtypes producing the highest precipitation estimates are those whose structures are most conducive to a long duration of sustained moderate to heavy rainfall. The event types were found to differ from those in the central United States in that the events were more often found to be more disorganized in the Northeast. One event type in particular, back-building with merging features, while not more disorganized than the previously recognized event types, offers promise for improved forecasting because its radar signature makes the duration of sustained heavy precipitation potentially easier to predict.

IPCC’s Twentieth-Century Climate Simulations: Varied Representations of North American Hydroclimate Variability

2006 ◽  
Vol 19 (16) ◽  
pp. 4041-4058 ◽  
Author(s):  
Alfredo Ruiz-Barradas ◽  
Sumant Nigam
Keyword(s):  
United States ◽  
Twentieth Century ◽  
North American ◽  
Warm Season ◽  
Precipitation Variability ◽  
Model Version ◽  
Central United States ◽  
Hydroclimate Variability ◽  
Moisture Fluxes ◽  
The U.S

Abstract The annual cycle of precipitation and the interannual variability of the North American hydroclimate during summer months are analyzed in coupled simulations of the twentieth-century climate. The state-of-the-art general circulation models, participating in the Fourth Assessment Report for the Intergovernmental Panel on Climate Change (IPCC), included in the present study are the U.S. Community Climate System Model version 3 (CCSM3), the Parallel Climate Model (PCM), the Goddard Institute for Space Studies model version EH (GISS-EH), and the Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL-CM2.1); the Met Office’s Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO-HadCM3); and the Japanese Model for Interdisciplinary Research on Climate version 3.2 [MIROC3.2(hires)]. Datasets with proven high quality such as NCEP’s North American Regional Reanalysis (NARR), and the Climate Prediction Center (CPC) U.S.–Mexico precipitation analysis are used as targets for simulations. Climatological precipitation is not easily simulated. While models capture winter precipitation very well over the U.S. northwest, they encounter failure over the U.S. southeast in the same season. Summer precipitation over the central United States and Mexico is also a great challenge for models, particularly the timing. In general the UKMO-HadCM3 is closest to the observations. The models’ potential in simulating interannual hydroclimate variability over North America during the warm season is varied and limited to the central United States. Models like PCM, and in particular UKMO-HadCM3, exhibit reasonably well the observed distribution and relative importance of remote and local contributions to precipitation variability over the region (i.e., convergence of remote moisture fluxes dominate over local evapotranspiration). However, in models like CCSM3 and GFDL-CM2.1 local contributions dominate over remote ones, in contrast with warm-season observations. In the other extreme are models like GISS-EH and MIROC3.2(hires) that prioritize the remote influence of moisture fluxes and neglect the local influence of land surface processes to the regional precipitation variability.

The Relationship between Cool and Warm Season Moisture over the Central United States, 1685–2015

2018 ◽  
Vol 31 (19) ◽  
pp. 7909-7924 ◽  
Author(s):  
Max C. A. Torbenson ◽  
David W. Stahle
Keyword(s):  
United States ◽  
Soil Moisture ◽  
Tree Ring ◽  
Land Surface ◽  
Warm Season ◽  
Instrumental Record ◽  
Moisture Balance ◽  
Central United States ◽  
The Relationship

Land surface feedbacks impart a significant degree of persistence between cool and warm season moisture availability in the central United States. However, the degree of correlation between these two variables is subject to major changes that appear to occur on decadal to multidecadal time scales, even in the relatively short 115-yr instrumental record. Tree-ring reconstructions have extended the limited observational record of long-term soil moisture levels, but such reconstructions do not resolve the seasonal differences in moisture conditions. We present two separate 331-yr-long seasonal moisture reconstructions for the central United States, based on sensitive subannual and annual tree-ring chronologies that have strong and separate seasonal moisture signals: an estimate of the long-term May soil moisture balance and a second estimate of the short-term June–August atmospheric moisture balance. The predictors used in each seasonal reconstruction are not significantly correlated with the alternate season target. Both reconstructions capture over 70% of the interannual variance in the instrumental data for the calibration period and also share significant decadal and multidecadal variability with the instrumental record in both the calibration and validation periods. The instrumental and reconstructed moisture levels are both positively correlated between spring and summer strongly enough to have potential value in seasonal prediction. However, the relationship between spring and summer moisture exhibits major decadal changes in strength and even sign that appear to be related to large-scale ocean–atmosphere dynamics associated with the Atlantic multidecadal oscillation.

The Precipitation Response over the Continental United States to Cold Tropical Pacific Sea Surface Temperatures

2014 ◽  
Vol 27 (13) ◽  
pp. 5036-5055 ◽  
Author(s):  
Hailan Wang ◽  
Siegfried Schubert
Keyword(s):  
United States ◽  
Warm Season ◽  
The United States ◽  
Tropical Pacific ◽  
Eastern United States ◽  
North Atlantic Subtropical High ◽  
Sst Variability ◽  
The Pacific ◽  
Central United States ◽  
Atmospheric Circulation Anomalies

The dominant pattern of SST variability in the Pacific during its cold phase produces pronounced precipitation deficits over the continental United States throughout the annual cycle. This study investigates the observed physical and dynamical processes through which the cold Pacific pattern affects U.S. precipitation, particularly the causes for the peak dry impacts in fall, as well as the nature of the differences between the summer and fall responses. Results show that the peak precipitation deficit over the United States during fall is primarily due to reduced atmospheric moisture transport from the Gulf of Mexico into the central and eastern United States and secondarily a reduction in local evaporation from land–atmosphere feedback. The former is associated with a strong and systematic low-level northeasterly flow anomaly over the southeastern United States that counteracts the northwest branch of the climatological North Atlantic subtropical high. The above northeasterly anomaly is maintained by both diabatic heating anomalies in the nearby intra-American seas and diabatic cooling anomalies in the tropical Pacific. In contrast, the modest summertime precipitation deficit over the central United States is mainly an intensification of the local dry anomaly in the preceding spring from local land–atmosphere feedback; the rather weak and disorganized atmospheric circulation anomalies over and to the south of the United States make little contribution. An evaluation of the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) AGCM simulations shows it to be deficient in simulating the warm season tropical convection responses over the intra-American seas to the cold Pacific pattern and thereby the precipitation responses over the United States, a problem that appears to be common to many AGCMs.

Sign in / Sign up

Export Citation Format

Share Document