Gravity Waves and Other Mechanisms Modulating the Diurnal Precipitation over One of the Rainiest Spots on Earth: Observations and Simulations in 2016

2020 ◽  
Vol 148 (9) ◽  
pp. 3933-3950
Author(s):  
Johanna Yepes ◽  
John F. Mejía ◽  
Brian Mapes ◽  
Germán Poveda
Keyword(s):  
Diurnal Cycle ◽  
Wrf Model ◽  
Early Morning ◽  
Weather Research And Forecasting ◽  
Near Surface ◽  
Additional Hypothesis ◽  
Convective Systems ◽  
Earth Observations ◽  
Diurnal Rainfall ◽  
Static Energy

ABSTRACT The diurnal cycle of precipitation and thermodynamic profiles over western Colombia are examined in new GPM satellite rainfall products, first-ever research balloon launches during 2016 over both sea and land, and numerical simulations with the Weather Research and Forecasting (WRF) Model. This paper evaluates the Mapes et al. mechanism for midnight–early morning coastal convection that propagates offshore: reduction of inhibition in the crests of lower-tropospheric internal waves. Shipborne balloon launches confirm the evening development of such inhibition by a warm overhang in saturation moist static energy (SMSE) near 700–800 hPa. This feature relaxes overnight, consistent with the disinhibition hypothesis for early morning rains. Over the coastal plain, soundings also show late afternoon increases in near-surface MSE large enough to predominate over the overhang’s inhibition effect, driving a second peak in the rainfall diurnal cycle. Parameterized convection simulations fail to simulate the observed coastal rainfall. Still, during a November 2016 wet spell, a cloud-permitting one-way nested 4 km simulation performs better, simulating morning coastal rainfall. In that simulation, however, early morning cooling in the 700–800 hPa layer appears mainly as a standing signal resembling the local radiative effect rather than as a propagating wave. We consider the additional hypothesis that the offshore propagation of that morning convection could involve advection or wind shear effects on organized convective systems. Strong easterlies at mountaintop level were indeed simulated, but that is one of the model’s strongest biases, so the mechanisms of the model’s partial success in simulating diurnal rainfall remain ambiguous.

scholarly journals Observation- and numerical-analysis-based dynamics of the Uttarkashi cloudburst

2015 ◽  
Vol 33 (6) ◽  
pp. 671-686 ◽  
Author(s):  
C. Chaudhuri ◽  
S. Tripathi ◽  
R. Srivastava ◽  
A. Misra
Keyword(s):  
Land Surface ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Moisture Condition ◽  
Near Surface ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
E Region ◽  
Triggering Mechanisms ◽  
Atmospheric Variables

Abstract. A Himalayan cloudburst event, which occurred on 3 August 2012 in the Uttarkashi (30.73° N, 78.45° E) region of Uttarakhand, India, was analyzed. The near-surface atmospheric variables were analyzed to study the formation, evolution, and triggering mechanisms of this cloudburst. In order to improve upon the understanding provided by the observations, numerical simulations were performed using the Weather Research and Forecasting (WRF) model, configured with a single domain at 18 km resolution. The model was tuned using variation of different parameterizations (convective, microphysical, boundary layer, radiation, and land surface), and different model options (number of vertical levels, and spin-up time), which resulted in a combination of parameters and options that best reproduced the observed diurnal characteristics of the near-surface atmospheric variables. Our study demonstrates the ability of WRF in forecasting precipitation, and resolving synoptic-scale and mesoscale interactions. In order to better understand the cloudburst, we configured WRF with multiply nested two-way-interacting domains (18, 6, 2 km) centered on the location of interest, and simulated the event with the best configuration derived earlier. The results indicate that two mesoscale convective systems originating from Madhya Pradesh and Tibet interacted over Uttarkashi and, under orographic uplifting and in the presence of favorable moisture condition, resulted in this cloudburst event.

scholarly journals In Situ Initiation of East Pacific Easterly Waves in a Regional Model

2017 ◽  
Vol 74 (2) ◽  
pp. 333-351 ◽  
Author(s):  
Adam V. Rydbeck ◽  
Eric D. Maloney ◽  
Ghassan J. Alaka
Keyword(s):  
Wrf Model ◽  
Warm Pool ◽  
Early Morning ◽  
Mesoscale Convective Systems ◽  
Weather Research And Forecasting ◽  
Easterly Waves ◽  
Convective Systems ◽  
East Pacific ◽  
Mesoscale Convective

Abstract The in situ generation of easterly waves (EWs) in the east Pacific (EPAC) is investigated using the Weather Research and Forecasting (WRF) Model. The sensitivity of the model to the suppression of EW forcing by locally generated convective disturbances is examined. Specifically, local forcing of EWs is removed by reducing the terrain height in portions of Central and South America to suppress robust sources of diurnal convective variability, most notably in the Panama Bight. High terrain contributes to the initiation of mesoscale convective systems in the early morning that propagate westward into the EPAC warm pool. When such mesoscale convective systems are suppressed in the model, EW variance is significantly reduced. This result suggests that EPAC EWs can be generated locally in association with higher-frequency convective disturbances, and these disturbances are determined to be an important source of EPAC EW variability. However, EPAC EW variability is not completely eliminated in such sensitivity experiments, indicating the importance for other sources of EW forcing, namely, EWs propagating into the EPAC from West Africa. Examination of the EW vorticity budget in the model suggests that nascent waves are zonally elongated and amplified by horizontal advection and vertical stretching of vorticity. Changes in the mean state between the control run and simulation with reduced terrain height also complicate interpretation of the results.

scholarly journals Advances in the WRF model for convection-resolving forecasting

2006 ◽  
Vol 7 ◽  
pp. 25-29 ◽  
Author(s):  
J. B. Klemp
Keyword(s):  
Wrf Model ◽  
Forecast Accuracy ◽  
Weather Forecast ◽  
Cumulus Parameterization ◽  
Weather Research And Forecasting ◽  
Convective Systems ◽  
Convective Processes ◽  
Forecast Models ◽  
Good Potential ◽  
Mesh Spacing

Abstract. The Weather Research and Forecasting (WRF) Model has been designed to be an efficient and flexible simulation system for use across a broad range of weather-forecast and idealized-research applications. Of particular interest is the use of WRF in nonhydrostatic applications in which moist-convective processes are treated explicitly, thereby avoiding the ambiguities of cumulus parameterization. To evaluate the capabilities of WRF for convection-resolving applications, real-time forecasting experiments have been conducted with 4 km horizontal mesh spacing for both convective systems in the central U.S. and for hurricanes approaching landfall in the southeastern U.S. These forecasts demonstrate a good potential for improving the forecast accuracy of the timing and location of these systems, as well as providing more detailed information on their structure and evolution that is not available in current coarser resolution operational forecast models.

scholarly journals PREDIKTIBILITAS CURAH HUJAN DIURNAL DI PULAU JAWA MENGGUNAKAN MODEL WRF [PREDICTIBILITY OF DIURNAL RAINFALL OVER JAVA ISLAND USING WRF]

2017 ◽  
Vol 14 (2) ◽  
pp. 57
Author(s):  
NFN Suaydhi
Keyword(s):  
Diurnal Cycle ◽  
Early Warning ◽  
Confidence Level ◽  
Early Warning System ◽  
Wrf Model ◽  
Warning System ◽  
Madden Julian Oscillation ◽  
Diurnal Cycles ◽  
Diurnal Rainfall ◽  
One Year

Indonesian region often experiences hydrometeorological disasters such as floods and landslides. To mitigate the losses from such disasters, an early warning system is needed. PSTA LAPAN has developed an early warning system called SADEWA (Satellite Disaster Early Warning System). The performance of this early warning system needs to be evaluated in order to increase the confidence level. The evaluation of the WRF performance in producing the prediction was carried out by analyzing the diurnal cycles of rainfall over Java and its surroundings using the results of WRF predictions implemented in SADEWA and GSMaP data for one year period (Maret 2014 Februari 2015). The contrasting diurnal cycles between Java island and its surrounding seas could be well simulated by the WRF model, both the amount and the frequency of the rainfall. However, the phase of diurnal cycle from the WRF prediction leads that of the observation by two hours and the amplitude of the simulated diurnal cycle is higher than the observed. The results also show that the WRF predictions could not simulate the effects of MJO (Madden-Julian Oscillation) on the diurnal cycles of rainfall over Java.ABSTRAKWilayah Indonesia sering mengalami bencana hidrometeorologi seperti banjir dan tanah longsor. Untuk mengurangi kerugian yang diakibatkan oleh kejadian bencana meteorologi diperlukan suatu sistem peringatan dini. PSTA LAPAN telah mengembangkan sebuah sistem peringatan dini yang diberi nama SADEWA (Satellite Disaster Early Warning System). Kinerja sistem peringatan dini seperti ini perlu dievaluasi agar tingkat kepercayaannya meningkat. Evaluasi kinerja hasil prediksi ini dilakukan dengan menganalisis siklus diurnal curah hujan di pulau Jawa dan sekitarnya pada data hasil prediksi WRF yang digunakan dalam SADEWA dan data GSMaP selama satu tahun (Maret 2014 Februari 2015). Siklus diurnal curah hujan yang kontras antara pulau Jawa dengan lautan sekitarnya mampu disimulasikan dengan baik oleh model WRF, baik dari jumlah maupun frekuensi curah hujannya. Namun fasa diurnal dari hasil prediksi WRF mendahului fasa data pengamatan sekitar dua jam dan mempunyai amplitudo lebih besar. Hasil analisis juga menunjukkan hasil prediksi WRF belum mampu mensimulasikan pengaruh MJO (Madden-Julian Oscillation) pada siklus diurnal curah hujan di Jawa.

The Diurnal Cycle of Rainfall and Convective Intensity according to Three Years of TRMM Measurements

2003 ◽  
Vol 16 (10) ◽  
pp. 1456-1475 ◽  
Author(s):  
Stephen W. Nesbitt ◽  
Edward J. Zipser
Keyword(s):  
Diurnal Cycle ◽  
Tropical Rainfall Measuring Mission ◽  
Early Morning ◽  
Convective Systems ◽  
Rain Gauges ◽  
Mesoscale Convective ◽  
Late Evening ◽  
Microwave Imager ◽  
Trmm Microwave Imager ◽  
Rain Rates

Abstract The Tropical Rainfall Measuring Mission (TRMM) satellite measurements from the precipitation radar and TRMM microwave imager have been combined to yield a comprehensive 3-yr database of precipitation features (PFs) throughout the global Tropics (±36° latitude). The PFs retrieved using this algorithm (which number nearly six million Tropicswide) have been sorted by size and intensity ranging from small shallow features greater than 75 km2 in area to large mesoscale convective systems (MCSs) according to their radar and ice scattering characteristics. This study presents a comprehensive analysis of the diurnal cycle of the observed precipitation features' rainfall amount, precipitation feature frequency, rainfall intensity, convective–stratiform rainfall portioning, and remotely sensed convective intensity, sampled Tropicswide from space. The observations are sorted regionally to examine the stark differences in the diurnal cycle of rainfall and convective intensity over land and ocean areas. Over the oceans, the diurnal cycle of rainfall has small amplitude, with the maximum contribution to rainfall coming from MCSs in the early morning. This increased contribution is due to an increased number of MCSs in the nighttime hours, not increasing MCS areas or conditional rain rates, in agreement with previous works. Rainfall from sub-MCS features over the ocean has little appreciable diurnal cycle of rainfall or convective intensity. Land areas have a much larger rainfall cycle than over the ocean, with a marked minimum in the midmorning hours and a maximum in the afternoon, slowly decreasing through midnight. Non-MCS features have a significant peak in afternoon instantaneous conditional rain rates (the mean rain rate in raining pixels), and convective intensities, which differs from previous studies using rain rates derived from hourly rain gauges. This is attributed to enhancement by afternoon heating. MCSs over land have a convective intensity peak in the late afternoon, however all land regions have MCS rainfall peaks that occur in the late evening through midnight due to their longer life cycle. The diurnal cycle of overland MCS rainfall and convective intensity varies significantly among land regions, attributed to MCS sensitivity to the varying environmental conditions in which they occur.

scholarly journals Modeling the Evolution and Life Cycle of Stable Cold Pools

2016 ◽  
Vol 31 (6) ◽  
pp. 1753-1769 ◽  
Author(s):  
Travis H. Wilson ◽  
Robert G. Fovell
Keyword(s):  
Relative Humidity ◽  
Wrf Model ◽  
Central Valley ◽  
Surface Fluxes ◽  
Weather Research And Forecasting ◽  
Near Surface ◽  
Cold Pools ◽  
Drainage Flows ◽  
Forested Region ◽  
Dry Bias

Abstract Stable cold pools in California’s Central Valley (CV) are conducive to freezing temperatures, high relative humidity, and, in some cases, fog. In this study it will be shown that the Weather Research and Forecasting (WRF) Model as commonly configured cannot reproduce such conditions because of a persistent warm and dry bias near the surface. It was found that removing horizontal diffusion, which by default operates on model levels and thus up and down the valley’s sides, can reduce but not entirely fix the problem. Other improvements include enhancing the near-surface vertical resolution and the surface–air coupling, as both directly control the surface fluxes, especially evaporation. However, these alterations actually have the largest impact in the forested region surrounding the Central Valley, and influence the nighttime relative humidity in the CV only indirectly via nocturnal drainage flows. While it is not clear how realistic are the increased evaporation in the forest or the drainage flows, how and why these alterations result in significantly improved relative humidity reconstructions within the Central Valley are shown.

scholarly journals Comparison of the Diurnal Precipitation Cycle in Convection-Resolving and Non-Convection-Resolving Mesoscale Models

2007 ◽  
Vol 135 (10) ◽  
pp. 3456-3473 ◽  
Author(s):  
Adam J. Clark ◽  
William A. Gallus ◽  
Tsing-Chang Chen
Keyword(s):  
United States ◽  
Spatial Correlation ◽  
Diurnal Cycle ◽  
Wrf Model ◽  
Correlation Coefficients ◽  
Weather Research And Forecasting ◽  
Grid Spacing ◽  
Diurnal Cycles ◽  
Central United States ◽  
Precipitation Cycle

Abstract The diurnal cycles of rainfall in 5-km grid-spacing convection-resolving and 22-km grid-spacing non-convection-resolving configurations of the Weather Research and Forecasting (WRF) model are compared to see if significant improvements can be obtained by using fine enough grid spacing to explicitly resolve convection. Diurnally averaged Hovmöller diagrams, spatial correlation coefficients computed in Hovmöller space, equitable threat scores (ETSs), and biases for forecasts conducted from 1 April to 25 July 2005 over a large portion of the central United States are used for the comparisons. A subjective comparison using Hovmöller diagrams of diurnally averaged rainfall show that the diurnal cycle representation in the 5-km configuration is clearly superior to that in the 22-km configuration during forecast hours 24–48. The superiority of the 5-km configuration is validated by much higher spatial correlation coefficients than in the 22-km configuration. During the first 24 forecast hours the 5-km model forecasts appear to be more adversely affected by model “spinup” processes than the 22-km model forecasts, and it is less clear, subjectively, which configuration has the better diurnal cycle representation, although spatial correlation coefficients are slightly higher in the 22-km configuration. ETSs in both configurations have diurnal oscillations with relative maxima occurring in both configurations at forecast hours corresponding to 0000–0300 LST, while biases also have diurnal oscillations with relative maxima (largest errors) in the 22-km (5-km) configuration occurring at forecast hours corresponding to 1200 (1800) LST. At all forecast hours, ETSs from the 22-km configuration are higher than those in the 5-km configuration. This inconsistency with some of the results obtained using the aforementioned spatial correlation coefficients reinforces discussion in past literature that cautions against using “traditional” verification statistics, such as ETS, to compare high- to low-resolution forecasts.

scholarly journals Diurnal Cycle of Summer Precipitation over Subtropical East Asia in CAM5

2013 ◽  
Vol 26 (10) ◽  
pp. 3159-3172 ◽  
Author(s):  
Weihua Yuan ◽  
Rucong Yu ◽  
Minghua Zhang ◽  
Wuyin Lin ◽  
Jian Li ◽  
...  
Keyword(s):  
East Asia ◽  
Diurnal Cycle ◽  
Large Scale ◽  
Early Morning ◽  
Convective Precipitation ◽  
Total Rainfall ◽  
Low Level ◽  
Resolution Model ◽  
Diurnal Rainfall ◽  
Stratiform Rainfall

Abstract The simulations of summertime diurnal cycle of precipitation and low-level winds by the Community Atmosphere Model, version 5, are evaluated over subtropical East Asia. The evaluation reveals the physical cause of the observed diurnal rainfall variation in East Asia and points to the source of model strengths and weaknesses. Two model versions with horizontal resolutions of 2.8° and 0.5° are used. The models can reproduce the diurnal phase of large-scale winds over East Asia, with an enhanced low-level southwesterly in early morning. Correspondingly, models successfully simulated the diurnal variation of stratiform rainfall with a maximum in early morning. However, the simulated convective rainfall occurs at local noontime, earlier than observations and with larger amplitude (normalized by the daily mean). As a result, models simulated a weaker diurnal cycle in total rainfall over the western plain of China due to an out-of-phase cancellation between convective and stratiform rainfalls and a noontime maximum of total rainfall over the eastern plain of China. Over the East China Sea, models simulated the early-morning maximum of convective precipitation and, together with the correct phase of the stratiform rainfall, they captured the diurnal cycle of total precipitation. The superposition of the stratiform and convective rainfalls also explains the observed diurnal cycle in total rainfall in East Asia. Relative to the coarse-resolution model, the high-resolution model simulated slight improvement in diurnal rainfall amplitudes, due to the larger amplitude of stratiform rainfall. The two models, however, suffer from the same major biases in rainfall diurnal cycles due to the convection parameterization.

scholarly journals Surface deposition of marine fog and its treatment in the Weather Research and Forecasting (WRF) model

2021 ◽  
Vol 21 (19) ◽  
pp. 14687-14702
Author(s):  
Peter A. Taylor ◽  
Zheqi Chen ◽  
Li Cheng ◽  
Soudeh Afsharian ◽  
Wensong Weng ◽  
...  
Keyword(s):  
Water Surface ◽  
Roughness Length ◽  
Deposition Velocity ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Water Droplets ◽  
Surface Deposition ◽  
Near Surface ◽  
Fog Water ◽  
Weather Research

Abstract. There have been many studies of marine fog, some using Weather Research and Forecasting (WRF) and other models. Several model studies report overpredictions of near-surface liquid water content (Qc), leading to visibility estimates that are too low. This study has found the same. One possible cause of this overestimation could be the treatment of a surface deposition rate of fog droplets at the underlying water surface. Most models, including the Advanced Research Weather Research and Forecasting (WRF-ARW) Model, available from the National Center for Atmospheric Research (NCAR), take account of gravitational settling of cloud droplets throughout the domain and at the surface. However, there should be an additional deposition as turbulence causes fog droplets to collide and coalesce with the water surface. A water surface, or any wet surface, can then be an effective sink for fog water droplets. This process can be parameterized as an additional deposition velocity with a model that could be based on a roughness length for water droplets, z0c, that may be significantly larger than the roughness length for water vapour, z0q. This can be implemented in WRF either as a variant of the Katata scheme for deposition to vegetation or via direct modifications in boundary-layer modules.

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