scholarly journals Dynamics of Upper-Level Frontogenesis in Baroclinic Waves

2016 ◽  
Vol 73 (7) ◽  
pp. 2699-2714 ◽  
Author(s):  
Mankin Mak ◽  
Yi Lu ◽  
Yi Deng
Keyword(s):  
Diabatic Heating ◽  
Weather Research And Forecasting ◽  
Baroclinic Wave ◽  
Baroclinic Waves ◽  
Structure And Dynamics ◽  
Upper Level ◽  
Vertically Propagating ◽  
Necessary And Sufficient ◽  
Stretching Process ◽  
High Potential Vorticity

Abstract This paper reports a diagnosis of the structure and dynamics of upper-level fronts (ULFs) simulated with a high-resolution Weather Research and Forecasting Model with diabatic heating versus one without diabatic heating. The ULFs of both simulations develop in about 6 days as integral parts of intensifying baroclinic waves. Each has a curvilinear structure along the southern edge of a relatively narrow long tongue of high potential vorticity in which stratospheric air is subducted to different tropospheric levels by synoptic-scale subsidence. It resembles a veil in the sky of varying thickness across the midsection upstream of the trough of the baroclinic wave. The 3D frontogenetical function is shown to be a necessary and sufficient metric for quantifying the rate of development of ULFs. Its value is mostly associated with the contribution of the 3D ageostrophic velocity component. Upper-level frontogenesis is attributable to the joint direct influence of the vortex-stretching process and the deformation property of the 3D ageostrophic flow component. The model also generates a spectrum of vertically propagating mesoscale gravity waves. The ULFs simulated with and without diabatic heating processes are qualitatively similar. The ULF is considerably more intense when there is heating. The heating, however, does not make a significant direct contribution to but indirectly does so through its impacts on the subsidence field of the baroclinic wave.

scholarly journals On the Quantification of Imbalance and Inertia–Gravity Waves Generated in Numerical Simulations of Moist Baroclinic Waves Using the WRF Model

2017 ◽  
Vol 74 (12) ◽  
pp. 4241-4263 ◽  
Author(s):  
Mohammad Mirzaei ◽  
Ali R. Mohebalhojeh ◽  
Christoph Zülicke ◽  
Riwal Plougonven
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Baroclinic Waves ◽  
Surface Front ◽  
The Difference ◽  
Upper Level ◽  
Upper Level Jet ◽  
Inertia Gravity Waves

Abstract Quantification of inertia–gravity waves (IGWs) generated by upper-level jet–surface front systems and their parameterization in global models of the atmosphere relies on suitable methods to estimate the strength of IGWs. A harmonic divergence analysis (HDA) that has been previously employed for quantification of IGWs combines wave properties from linear dynamics with a sophisticated statistical analysis to provide such estimates. A question of fundamental importance that arises is how the measures of IGW activity provided by the HDA are related to the measures coming from the wave–vortex decomposition (WVD) methods. The question is addressed by employing the nonlinear balance relations of the first-order δ–γ, the Bolin–Charney, and the first- to third-order Rossby number expansion to carry out WVD. The global kinetic energy of IGWs given by the HDA and WVD are compared in numerical simulations of moist baroclinic waves by the Weather Research and Forecasting (WRF) Model in a channel on the f plane. The estimates of the HDA are found to be 2–3 times smaller than those of the optimal WVD. This is in part due to the absence of a well-defined scale separation between the waves and vortical flows, the IGW estimates by the HDA capturing only the dominant wave packets and with limited scales. It is also shown that the difference between the HDA and WVD estimates is related to the width of the IGW spectrum.

scholarly journals Two Issues Concerning Surface Frontogenesis

2017 ◽  
Vol 74 (9) ◽  
pp. 2967-2987 ◽  
Author(s):  
Mankin Mak ◽  
Yi Lu ◽  
Yi Deng
Keyword(s):  
Diabatic Heating ◽  
Cold Front ◽  
Model Simulation ◽  
Wrf Model ◽  
Baroclinic Wave ◽  
Steering Flow ◽  
Warm Front ◽  
Surface Front ◽  
Upper Level ◽  
Ageostrophic Circulation

Abstract With the Weather Research and Forecasting (WRF) Model specifically configured to simulate the intensification and evolution of an extratropical baroclinic wave, this study first investigates why cold fronts are characteristically longer, narrower, and more intense than warm fronts in the extratropical atmosphere. It is found that the differential thermal advection by the geostrophic and ageostrophic wind components in the two frontal regions results in a greater thermal contrast across the cold front. The length of the cold front is essentially the length scale of the intensifying baroclinic wave (i.e., on the order of radius of deformation). The frontal system as a whole moves eastward under the influence of a steering flow. In addition, the cold front outpaces the warm front eastward, making the western portion of the warm front progressively occluded and the eastern portion of the warm front shorter. The dynamical processes tend to move the cold front eastward, whereas the diabatic heating processes tend to move it westward, contributing to the narrowness of the cold front. This study also investigates whether, how, and why an upper-level front (ULF) would synergistically interact with a surface front (SF). It is found that a favorable circumstance for such interaction to occur in an observed extratropical cyclone and in the WRF Model simulation is when the ULF and SF are roughly parallel to one another with the ULF aloft located a few hundred kilometers to the west of the SF. The relative importance of “forcing” for the ageostrophic circulation associated with the geostrophic circulation, diabatic heating, and friction are diagnosed in such interaction.

scholarly journals Diagnosis of Track Forecast Errors for Tropical Cyclone Rita (2005) Using GEFS Reforecasts

2015 ◽  
Vol 30 (5) ◽  
pp. 1334-1354 ◽  
Author(s):  
Thomas J. Galarneau ◽  
Thomas M. Hamill
Keyword(s):  
Tropical Cyclone ◽  
Weather Prediction ◽  
Weather Research And Forecasting ◽  
Track Forecast ◽  
Forecast Errors ◽  
Subtropical Anticyclone ◽  
Cutoff Low ◽  
Layer Flow ◽  
Upper Level ◽  
Mass Evacuation

Abstract Analysis and diagnosis of the track forecasts for Tropical Cyclone (TC) Rita (2005) from the Global Ensemble Forecast System (GEFS) reforecast dataset is presented. The operational numerical weather prediction guidance and GEFS reforecasts initialized at 0000 UTC 20–22 September 2005, 2–4 days prior to landfall, were all characterized by a persistent left-of-track error. The numerical guidance indicated a significant threat of landfall for the Houston, Texas, region on 24 September. The largest mass evacuation in U.S. history was ordered, with the evacuation resulting in more fatalities than TC Rita itself. TC Rita made landfall along the Texas–Louisiana coastal zone on 24 September. This study utilizes forecasts from the GEFS reforecast and a high-resolution regional reforecast. The regional reforecast was generated using the Advanced Hurricane Weather Research and Forecasting Model (AHW) with the GEFS reforecasts providing the initial and boundary conditions. The results show that TC Rita’s track was sensitive to errors in both the synoptic-scale flow and TC intensity. Within the GEFS reforecast ensemble, the nonrecurving members were characterized by a midlevel subtropical anticyclone that extended too far south and west over the southern United States, and an upper-level cutoff low west and anticyclone east of TC Rita that were too weak. The AHW regional reforecast ensemble further highlighted the role of intensity and steering-layer depth in TC Rita’s track. While the AHW forecast was initialized with a TC that was too weak, the ensemble members that were able to intensify TC Rita more rapidly produced a better track forecast because the TCs followed a deeper steering-layer flow.

scholarly journals Impacts of Stochastic Mixing in Idealized Convection-Permitting Simulations of Squall Lines

2020 ◽  
Vol 148 (12) ◽  
pp. 4971-4994
Author(s):  
McKenna W. Stanford ◽  
Hugh Morrison ◽  
Adam Varble
Keyword(s):  
Squall Line ◽  
Weather Research And Forecasting ◽  
Cold Pool ◽  
Multiplicative Factor ◽  
Mesoscale Structure ◽  
Squall Lines ◽  
Mixing Coefficients ◽  
Horizontal Mixing ◽  
Upper Level ◽  
Inflow Jet

AbstractThis study investigates impacts of altering subgrid-scale mixing in “convection-permitting” kilometer-scale horizontal-grid-spacing (Δh) simulations by applying either constant or stochastic multiplicative factors to the horizontal mixing coefficients within the Weather Research and Forecasting Model. In quasi-idealized 1-km Δh simulations of two observationally based squall-line cases, constant enhanced mixing produces larger updraft cores that are more dilute at upper levels, weakens the cold pool, rear-inflow jet, and front-to-rear flow of the squall line, and degrades the model’s effective resolution. Reducing mixing by a constant multiplicative factor has the opposite effect on all metrics. Completely turning off parameterized horizontal mixing produces bulk updraft statistics and squall-line mesoscale structure closest to an LES “benchmark” among all 1-km simulations, although the updraft cores are too undilute. The stochastic mixing scheme, which applies a multiplicative factor to the mixing coefficients that varies stochastically in time and space, is employed at 0.5-, 1-, and 2-km Δh. It generally reduces midlevel vertical velocities and enhances upper-level vertical velocities compared to simulations using the standard mixing scheme, with more substantial impacts at 1- and 2-km Δh compared to 0.5-km Δh. The stochastic scheme also increases updraft dilution to better agree with the LES for one case, but has less impact on the other case. Stochastic mixing acts to weaken the cold pool but without a significant impact on squall-line propagation. It also does not affect the model’s overall effective resolution unlike applying constant multiplicative factors to the mixing coefficients.

scholarly journals Polar Winds: Airborne Doppler Wind Lidar Missions in the Arctic for Atmospheric Observations and Numerical Model Comparisons

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1141
Author(s):  
Steven Greco ◽  
George D. Emmitt ◽  
Alice DuVivier ◽  
Keith Hines ◽  
Michael Kavaya
Keyword(s):  
Wrf Model ◽  
The Arctic ◽  
Weather Research And Forecasting ◽  
Dynamic Features ◽  
Wind Retrieval ◽  
Atmospheric Observations ◽  
Wind Lidar ◽  
Upper Level ◽  
Upper Level Jet ◽  
Doppler Wind Lidar

During October–November 2014 and May 2015, NASA sponsored and conducted a pair of airborne campaigns called Polar Winds to investigate atmospheric circulations, particularly in the boundary layer, over the Arctic using NASA’s Doppler Aerosol WiNd (DAWN) lidar. A description of the campaigns, the DAWN instrument, wind retrieval methods and data processing is provided. During the campaigns, the DAWN instrument faced backscatter sensitivity issues in the low aerosol conditions that were fairly frequent in the 2–6 km altitude range. However, when DAWN was able to make measurements, comparisons with dropsondes show good agreement and very low bias and supports the use of an airborne Doppler wind lidar such as DAWN that can provide profiles with high velocity precision, ~65 m vertical resolution and horizontal spacing as fine as 3–7 km. Case study analyses of a Greenland tip jet, barrier winds and an upper level jet are presented and show how, despite sensitivity issues, DAWN data can be confidently used in diagnostic studies of dynamic features in the Arctic. Comparisons with both an operational and research Weather Research and Forecasting (WRF) model for these events also show the potential for utilization in model validation. The sensitivity issues of the DAWN laser have since been corrected.

scholarly journals Eurasian Cooling Linked with Arctic Warming: Insights from PV Dynamics

2020 ◽  
Vol 33 (7) ◽  
pp. 2627-2644
Author(s):  
Yongkun Xie ◽  
Guoxiong Wu ◽  
Yimin Liu ◽  
Jianping Huang
Keyword(s):  
Vertical Structure ◽  
Diabatic Heating ◽  
Linear Trend ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
The Arctic ◽  
Arctic Warming ◽  
Circulation Change ◽  
General Dynamics ◽  
Upper Level

AbstractThe three-dimensional connections between Eurasian cooling and Arctic warming since 1979 were investigated using potential vorticity (PV) dynamics. We found that Eurasian cooling can be regulated by Arctic warming through PV adaptation and PV advection. Here, PV adaptation refers to the adaptation of PV to forcing and coherent dynamic–thermodynamic adaptation to PV change. In a PV perspective, first, the anticyclonic circulation change over the Arctic is produced by a negative PV change through PV adaptation, in which the change means the linear trend from 1979 to 2017. The negative PV change is directly regulated by Arctic warming because the vertical structure of Arctic warming is stronger at lower levels, which generates a negative PV change through the diabatic heating effect. Second, the circulation change produces a change in horizontal PV advection due to the existence of climatological PV gradients. Thus, as a balanced result, both the circulation change and PV change extend to the midlatitudes through horizontal PV advection and PV adaptation. Eventually, Eurasian cooling at the surface and in the lower troposphere is dominated by PV changes at the surface through PV adaptation. Meanwhile, enhanced Eurasian cooling in the middle troposphere is dominated by top-down influences of upper-level PV change through PV adaptation. Nevertheless, the upper-level PV changes are still contributed to by horizontal PV advection associated with Arctic warming. Overall, the general dynamics connecting Eurasian cooling with Arctic warming are demonstrated in a PV view.

scholarly journals Assessing the Effects of Microphysical Scheme on Convective and Stratiform Characteristics in a Mei-Yu Rainfall Combining WRF Simulation and Field Campaign Observations

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Lin Liu ◽  
Chunze Lin ◽  
Yongqing Bai ◽  
Dengxin He
Keyword(s):  
Wrf Model ◽  
Cloud Microphysics ◽  
Middle Level ◽  
Weather Research And Forecasting ◽  
Field Campaign ◽  
Microphysical Properties ◽  
Double Moment ◽  
Storm Dynamics ◽  
Precipitation Structure ◽  
Upper Level

Microphysics parameterization becomes increasingly important as the model grid spacing increases toward convection-resolving scales. Using observations from a field campaign for Mei-Yu rainfall in China, four bulk cloud microphysics schemes in the Weather Research and Forecasting (WRF) model were evaluated with respect to their ability to simulate precipitation, structure, and cloud microphysical properties over convective and stratiform regimes. These are the Thompson (THOM), Morrison graupel/hail (MOR_G/H), Stony Brook University (SBU_YLIN), and WRF double-moment six-class microphysics graupel/hail (WDM6_G/H). All schemes were able to predict the rain band but underestimated the total precipitation by 23%–35%. This is mainly attributed to the underestimation of stratiform precipitation and overestimation of convective rain. For the vertical distribution of radar reflectivity, many problems remain, such as lower reflectivity values aloft in both convective and stratiform regions and higher reflectivity values at middle level. Each bulk scheme has its advantages and shortcomings for different cloud regimes. Overall, the discrepancies between model output and observations mostly exist in the midlevel to upper level, which results from the inability of the model to accurately represent the particle size distribution, ice processes, and storm dynamics. Further observations from major field campaigns and more detailed evaluation are still necessary.

scholarly journals Comments on “Dynamics of Upper-Level Frontogenesis in Baroclinic Waves”

2017 ◽  
Vol 74 (1) ◽  
pp. 309-312 ◽  
Author(s):  
Andrea Buzzi
Keyword(s):  
Potential Temperature ◽  
Horizontal Gradient ◽  
Baroclinic Waves ◽  
Formation And Evolution ◽  
Upper Level

Abstract A recent paper by Mak et al. grants the opportunity to discuss two different definitions of the frontogenetical function proposed in the literature to study the formation and evolution of upper-level fronts. This comment exposes some problems that, in this author’s opinion, are related to the use of the Lagrangian tendency of the 3D (in place of horizontal) gradient of potential temperature, as adopted in the Mak et al. paper.

Eurasian cooling linked with Arctic warming: Insights from PV dynamics

2020 ◽  
Author(s):  
Yongkun Xie ◽  
Guoxiong Wu ◽  
Yimin Liu
Keyword(s):  
Vertical Structure ◽  
Diabatic Heating ◽  
Linear Trend ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
The Arctic ◽  
Arctic Warming ◽  
Circulation Change ◽  
General Dynamics ◽  
Upper Level

<p>The three-dimensional connections between Eurasian cooling and Arctic warming since 1979 were investigated using potential vorticity (PV) dynamics. We found that Eurasian cooling can be regulated by Arctic warming through PV adaptation and PV advection. Here, PV adaptation refers to the adaptation of PV to forcing and coherent dynamic/thermodynamic adaptation to PV change. In a PV perspective, first, the anticyclonic circulation change over the Arctic is produced by a negative PV change through PV adaptation, in which the change means the linear trend from 1979~2017. The negative PV change is directly regulated by Arctic warming because the vertical structure of Arctic warming is stronger at lower levels, which generates a negative PV change through the diabatic heating effect. Second, the circulation change produces a change in horizontal PV advection due to the existence of climatological PV gradients. Thus, as a balanced result, both the circulation change and PV change extend to mid-latitude through horizontal PV advection and PV adaptation. Eventually, Eurasian cooling at the surface and in the lower troposphere is dominated by PV changes at the surface through PV adaptation. Meanwhile, enhanced Eurasian cooling in the middle troposphere is dominated by top-down influences of upper-level PV change through PV adaptation. Nevertheless, the upper-level PV changes are still contributed by horizontal PV advection associated with Arctic warming. Overall, the general dynamics connecting Eurasian cooling with Arctic warming is demonstrated in a PV view.</p>

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