Downdrafts and the Evolution of Boundary Layer Thermodynamics in Hurricane Earl (2010) before and during Rapid Intensification

Abstract Using a combination of NOAA P-3 aircraft tail Doppler radar, NOAA and NASA dropsondes, and buoy- and drifter-based sea surface temperature data, different types of downdrafts and their influence on boundary layer (BL) thermodynamics are examined in Hurricane Earl (2010) during periods prior to rapid intensification [RI; a 30-kt (15.4 m s−1) increase in intensity over 24 h] and during RI. Before RI, the BL was generally warm and moist. The largest hindrances for intensification are convectively driven downdrafts inside the radius of maximum winds (RMW) and upshear-right quadrant, and vortex-tilt-induced downdrafts outside the RMW in the upshear-left quadrant. Possible mechanisms for overcoming the low entropy (θe) air induced by these downdrafts are BL recovery through air–sea enthalpy fluxes and turbulent mixing by atmospheric eddies. During RI, convective downdrafts of varying strengths in the upshear-left quadrant had differing effects on the low-level entropy and surface heat fluxes. Interestingly, the stronger downdrafts corresponded with maximums in 10-m θe. It is hypothesized that the large amount of evaporation in a strong (>2 m s−1) downdraft underneath a precipitation core can lead to high amounts of near-surface specific humidity. By contrast, weaker downdrafts corresponded with minimums in 10-m θe, likely because they contained lower evaporation rates. Since weak and dry downdrafts require more surface fluxes to recover the low entropy air than strong and moist downdrafts, they are greater hindrances to storm intensification. This study emphasizes how different types of downdrafts are tied to hurricane intensity change through their modification of BL thermodynamics.

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Impact of Parameterized Boundary Layer Structure on Tropical Cyclone Rapid Intensification Forecasts in HWRF

Monthly Weather Review ◽

10.1175/mwr-d-16-0129.1 ◽

2017 ◽

Vol 145 (4) ◽

pp. 1413-1426 ◽

Cited By ~ 24

Author(s):

Jun A. Zhang ◽

Robert F. Rogers ◽

Vijay Tallapragada

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

Inner Core ◽

Layer Structure ◽

Intensity Change ◽

Rapid Intensification ◽

Near Surface ◽

Boundary Layer Structure ◽

Tangential Wind ◽

The Impact

Abstract This study evaluates the impact of the modification of the vertical eddy diffusivity (Km) in the boundary layer parameterization of the Hurricane Weather Research and Forecasting (HWRF) Model on forecasts of tropical cyclone (TC) rapid intensification (RI). Composites of HWRF forecasts of Hurricanes Earl (2010) and Karl (2010) were compared for two versions of the planetary boundary layer (PBL) scheme in HWRF. The results show that using a smaller value of Km, in better agreement with observations, improves RI forecasts. The composite-mean, inner-core structures for the two sets of runs at the time of RI onset are compared with observational, theoretical, and modeling studies of RI to determine why the runs with reduced Km are more likely to undergo RI. It is found that the forecasts with reduced Km at the RI onset have a shallower boundary layer with stronger inflow, more unstable near-surface air outside the eyewall, stronger and deeper updrafts in regions farther inward from the radius of maximum wind (RMW), and stronger boundary layer convergence closer to the storm center, although the mean storm intensity (as measured by the 10-m winds) is similar for the two groups. Finally, it is found that the departure of the maximum tangential wind from the gradient wind at the eyewall, and the inward advection of angular momentum outside the eyewall, is much larger in the forecasts with reduced Km. This study emphasizes the important role of the boundary layer structure and dynamics in TC intensity change, supporting recent studies emphasizing boundary layer spinup mechanism, and recommends further improvement to the HWRF PBL physics.

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Intraseasonal Variability in Coupled GCMs: The Roles of Ocean Feedbacks and Model Physics

Journal of Climate ◽

10.1175/jcli-d-13-00760.1 ◽

2014 ◽

Vol 27 (13) ◽

pp. 4970-4995 ◽

Cited By ~ 52

Author(s):

Charlotte A. DeMott ◽

Cristiana Stan ◽

David A. Randall ◽

Mark D. Branson

Keyword(s):

Indian Ocean ◽

General Circulation ◽

Sensible Heat Flux ◽

General Circulation Models ◽

Ocean Model ◽

Surface Fluxes ◽

Heat Fluxes ◽

Specific Humidity ◽

Sensible Heat ◽

Near Surface

The interaction of ocean coupling and model physics in the simulation of the intraseasonal oscillation (ISO) is explored with three general circulation models: the Community Atmospheric Model, versions 3 and 4 (CAM3 and CAM4), and the superparameterized CAM3 (SPCAM3). Each is integrated coupled to an ocean model, and as an atmosphere-only model using sea surface temperatures (SSTs) from the coupled SPCAM3, which simulates a realistic ISO. For each model, the ISO is best simulated with coupling. For each SST boundary condition, the ISO is best simulated in SPCAM3. Near-surface vertical gradients of specific humidity, [Formula: see text] (temperature, [Formula: see text]), explain ~20% (50%) of tropical Indian Ocean latent (sensible) heat flux variance, and somewhat less of west Pacific variance. In turn, local SST anomalies explain ~5% (25%) of [Formula: see text] [Formula: see text] variance in coupled simulations, and less in uncoupled simulations. Ergo, latent and sensible heat fluxes are strongly controlled by wind speed fluctuations, which are largest in the coupled simulations, and represent a remote response to coupling. The moisture budget reveals that wind variability in coupled simulations increases east-of-convection midtropospheric moistening via horizontal moisture advection, which influences the direction and duration of ISO propagation. These results motivate a new conceptual model for the role of ocean feedbacks on the ISO. Indian Ocean surface fluxes help developing convection attain a magnitude capable of inducing the circulation anomalies necessary for downstream moistening and propagation. The “processing” of surface fluxes by model physics strongly influences the moistening details, leading to model-dependent responses to coupling.

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The Great Plains Irrigation Experiment (GRAINEX)

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-20-0041.1 ◽

2021 ◽

pp. 1-66

Author(s):

Eric Rappin ◽

Rezaul Mahmood ◽

Udaysankar Nair ◽

Roger A. Pielke ◽

William Brown ◽

...

Keyword(s):

Boundary Layer ◽

Great Plains ◽

Growing Season ◽

Layer Growth ◽

Surface Fluxes ◽

Heat Fluxes ◽

Irrigated Agriculture ◽

Strong Impact ◽

Near Surface

AbstractExtensive expansion in irrigated agriculture has taken place over the last half century. Due to increased irrigation and resultant land use land cover change, the central United States has seen a decrease in temperature and changes in precipitation during the second half of 20th century. To investigate the impacts of widespread commencement of irrigation at the beginning of the growing season and continued irrigation throughout the summer on local and regional weather, the Great Plains Irrigation Experiment (GRAINEX) was conducted in the spring and summer of 2018 in southeastern Nebraska. GRAINEX consisted of two, 15-day intensive observation periods. Observational platforms from multiple agencies and universities were deployed to investigate the role of irrigation in surface moisture content, heat fluxes, diurnal boundary layer evolution, and local precipitation.This article provides an overview of the data collected and an analysis of the role of irrigation in land-atmosphere interactions on time scales from the seasonal to the diurnal. The analysis shows that a clear irrigation signal was apparent during the peak growing season in mid-July. This paper shows the strong impact of irrigation on surface fluxes, near-surface temperature and humidity, as well as boundary layer growth and decay.

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ESTIMATIVA DA PARTIÇÃO DE ENERGIA NA SUPERFÍCIE

Ciência e Natura ◽

10.5902/2179460x20298 ◽

2016 ◽

Vol 38 ◽

pp. 412

Author(s):

Daiane De Vargas Brondani ◽

Otávio Costa Acevedo ◽

Fabíola Valente

Keyword(s):

Boundary Layer ◽

Latent Heat ◽

Convective Boundary Layer ◽

Method Development ◽

Surface Fluxes ◽

Heat Fluxes ◽

Specific Humidity ◽

Ratio Method ◽

Convective Boundary ◽

Monthly Scale

This paper is a complementary analysis to method development, which proposes to estimate the energy partition on the surface by Bowen ratio method and height of convective boundary layer on the monthly scale based on the average temporal evolution of the variables air temperature and specific humidity. The basic hypothesis is that the evolution of these quantities is controlled solely by the convergence of surface fluxes of sensible and latent heat. This assumption is valid for monthly scale and in regions of middle latitudes away from the coast. Thus, it is assumed that the advective terms of the balance equation of these quantities in the convective boundary layer, the prefrontal situations and post-frontal have opposite sign. Therefore, using for a longer time scale than the typical scale of the passage of synoptic systems, the cancellation terms of hypothesis can be tested. In this study, the method is applied to the region of Santa Maria, where it is assumed that the conditions allowing despise the advective terms in monthly scale are valid. When testing the method on different time scales: 5,10,15,20 and 30 days, smaller errors temperature and specific humidity were for 15 and 30 days, while the sensible heat and latent heat fluxes showed lower relative errors at 20 and 30 days, respectively.

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Observations of Infrared Sea Surface Temperature and Air–Sea Interaction in Hurricane Edouard (2014) Using GPS Dropsondes

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0211.1 ◽

2017 ◽

Vol 34 (6) ◽

pp. 1333-1349 ◽

Cited By ~ 20

Author(s):

Jun A. Zhang ◽

Joseph J. Cione ◽

Evan A. Kalina ◽

Eric W. Uhlhorn ◽

Terry Hock ◽

...

Keyword(s):

Boundary Layer ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Surface Flux ◽

Surface Fluxes ◽

Sea Surface ◽

Intensity Change ◽

Sensor Technology ◽

Near Surface ◽

Thermodynamic Structure

AbstractThis study highlights infrared sensor technology incorporated into the global positioning system (GPS) dropsonde platforms to obtain sea surface temperature (SST) measurements. This modified sonde (IRsonde) is used to improve understanding of air–sea interaction in tropical cyclones (TCs). As part of the Sandy Supplemental Program, IRsondes were constructed and then deployed during the 2014 hurricane season. Comparisons between SSTs measured by collocated IRsondes and ocean expendables show good agreement, especially in regions with no rain contamination. Surface fluxes were estimated using measurements from the IRsondes and AXBTs via a bulk method that requires measurements of SST and near-surface (10 m) wind speed, temperature, and humidity. The evolution of surface fluxes and their role in the intensification and weakening of Hurricane Edouard (2014) are discussed in the context of boundary layer recovery. The study’s result emphasizes the important role of surface flux–induced boundary layer recovery in regulating the low-level thermodynamic structure that is tied to the asymmetry of convection and TC intensity change.

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Sensitivity of an Idealized Tropical Cyclone to the Configuration of the Global Forecast System–Eddy Diffusivity Mass Flux Planetary Boundary Layer Scheme

Atmosphere ◽

10.3390/atmos12020284 ◽

2021 ◽

Vol 12 (2) ◽

pp. 284

Author(s):

Evan A. Kalina ◽

Mrinal K. Biswas ◽

Jun A. Zhang ◽

Kathryn M. Newman

Keyword(s):

Boundary Layer ◽

Planetary Boundary Layer ◽

Weather Prediction ◽

Intensity Change ◽

Rapid Intensification ◽

Forecast System ◽

Stability Functions ◽

Non Local ◽

The Stability ◽

Heat And Moisture

The intensity and structure of simulated tropical cyclones (TCs) are known to be sensitive to the planetary boundary layer (PBL) parameterization in numerical weather prediction models. In this paper, we use an idealized version of the Hurricane Weather Research and Forecast system (HWRF) with constant sea-surface temperature (SST) to examine how the configuration of the PBL scheme used in the operational HWRF affects TC intensity change (including rapid intensification) and structure. The configuration changes explored in this study include disabling non-local vertical mixing, changing the coefficients in the stability functions for momentum and heat, and directly modifying the Prandtl number (Pr), which controls the ratio of momentum to heat and moisture exchange in the PBL. Relative to the control simulation, disabling non-local mixing produced a ~15% larger storm that intensified more gradually, while changing the coefficient values used in the stability functions had little effect. Varying Pr within the PBL had the greatest impact, with the largest Pr (~1.6 versus ~0.8) associated with more rapid intensification (~38 versus 29 m s−1 per day) but a 5–10 m s−1 weaker intensity after the initial period of strengthening. This seemingly paradoxical result is likely due to a decrease in the radius of maximum wind (~15 versus 20 km), but smaller enthalpy fluxes, in simulated storms with larger Pr. These results underscore the importance of measuring the vertical eddy diffusivities of momentum, heat, and moisture under high-wind, open-ocean conditions to reduce uncertainty in Pr in the TC PBL.

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Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0122.1 ◽

2019 ◽

Vol 77 (3) ◽

pp. 1081-1100 ◽

Cited By ~ 1

Author(s):

Neil P. Lareau

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Latent Heat ◽

Surface Fluxes ◽

Heat Fluxes ◽

Cloud Base ◽

Cumulus Convection ◽

Mixing Ratio ◽

Convective Boundary ◽

Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

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Uncertainty Characterization of HOAPS-3.3 Latent Heat Flux Related Parameters

10.5194/amt-2017-176 ◽

2017 ◽

Author(s):

Julian Kinzel ◽

Marc Schröder ◽

Karsten Fennig ◽

Axel Andersson ◽

Rainer Hollmann

Keyword(s):

Latent Heat ◽

Heat Fluxes ◽

Specific Humidity ◽

Boreal Winter ◽

Western Boundary ◽

Near Surface ◽

In Situ Data ◽

Uncertainty Measures ◽

Global Mean

Abstract. Latent heat fluxes (LHF) are one of the main contributors to the global energy budget. As the density of LHF measurements over the global oceans is generally poor, the potential of remotely sensed LHF for meteorological applications is enormous. However, to date none of the available satellite products include estimates of systematic, random retrieval, and sampling uncertainties, all of which are essential for assessing their quality. Here, this challenge is taken on by applying regionally independent multi-dimensional bias analyses to LHF-related parameters (wind speed U, near-surface specific humidity qa, and sea surface saturation specific humidity qs) of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite (HOAPS) climatology. In connection with multiple triple collocation analyses, it is demonstrated how both instantaneous (gridded) uncertainty measures may be assigned to each pixel (grid box). A high-quality in situ data archive including buoys and selected ships serves as the ground reference. Results show that systematic LHF uncertainties range between 15–50 W m-2 with a global mean of 25 W m-2. Local maxima are mainly found over the subtropical ocean basins as well as along the western boundary currents. Investigations indicate that contributions by qa (U) to the overall LHF uncertainty are in the order of 60 % (25 %). From an instantaneous point of view, random retrieval uncertainties are specifically large over the subtropics with a global average of 37 W m-2. In a climatological sense, their magnitudes become negligible, as do respective sampling uncertainties. Time series analyses show footprints of climate events, such as the strong El Niño during 1997/98. Regional and seasonal analyses suggest that largest total (i.e., systematic + instantaneous random) LHF uncertainties are seen over the Gulf Stream and the Indian monsoon region during boreal winter. In light of the uncertainty measures, the observed continuous global mean LHF increase up to 2009 needs to be treated with caution. First intercomparisons to other LHF climatologies (in situ, satellite) reveal overall resemblance with few, yet distinct exceptions.

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The Role of Latent Heat Flux in Tropical Cyclogenesis over the Western North Pacific: Comparison of Developing versus Non-Developing Disturbances

Journal of Marine Science and Engineering ◽

10.3390/jmse7020028 ◽

2019 ◽

Vol 7 (2) ◽

pp. 28 ◽

Cited By ~ 5

Author(s):

Si Gao ◽

Shengbin Jia ◽

Yanyu Wan ◽

Tim Li ◽

Shunan Zhai ◽

...

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

North Pacific ◽

Western North Pacific ◽

Specific Humidity ◽

Near Surface ◽

Tangential Wind

The possible role of air–sea latent heat flux (LHF) in tropical cyclone (TC) genesis over the western North Pacific (WNP) is investigated using state-of-the-art satellite and analysis datasets. The authors conducted composite analyses of several meteorological variables after identifying developing and non-developing tropical disturbances from June to October of the period 2000 to 2009. Compared to the non-developing disturbances, increased LHF underlying the developing disturbances enhances boundary–layer specific humidity. The secondary circulation then transports more boundary–layer moisture inward and upward and, thus, induces a stronger moist core in the middle troposphere. Accordingly, the air in the core region ascends following a warmer moist adiabat than that in the environment and results in a stronger upper-level warm core, which is associated with a stronger near-surface tangential wind based on the thermal wind balance. This enlarges the magnitude and negative radial gradient of LHF and, thereby, further increases boundary–layer specific humidity. A tropical depression forms when the near-surface tangential wind increases to a certain extent as a result of the continuing positive feedback between near-surface wind and LHF. The results suggest an important role of wind-driven LHF in TC genesis over the WNP.

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Importance of Using Observations of Mixing Depths in order to Avoid Large Prediction Errors by a Transport and Dispersion Model

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2008jtecha1134.1 ◽

2009 ◽

Vol 26 (1) ◽

pp. 22-32 ◽

Cited By ~ 15

Author(s):

J. M. White ◽

J. F. Bowers ◽

S. R. Hanna ◽

J. K. Lundquist

Keyword(s):

Boundary Layer ◽

Atmospheric Transport ◽

Similarity Theory ◽

Dispersion Model ◽

Heat Fluxes ◽

Synoptic Situation ◽

Prediction Errors ◽

Sensible Heat ◽

Mixing Depth ◽

Near Surface

Abstract The mixing depth of the boundary layer is an input to most atmospheric transport and dispersion (ATD) models, which obtain mixing depths in one of four ways: 1) observations by radiosondes, sodars, or other devices; 2) simulations by regional or mesoscale meteorological models; 3) parameterizations based on boundary layer similarity theory; or 4) climatological averages. This paper describes a situation during a field experiment when exceptionally low mixing depths persisted in the morning and led to relatively high observed tracer concentrations. The low mixing depths were caused by synoptic effects associated with a nearby stationary front and the outflow from a mesoscale thunderstorm complex located 20–50 km away. For the same time period, the ATD model-parameterized mixing depth was a factor of 5–10 higher, leading to predicted concentrations that were less than the observations by a factor of 5–10. The synoptic situation is described and local radiosonde and radar observations of mixing depth are presented, including comparisons with other more typical days. Time series of local observations of near-surface sensible heat fluxes are also plotted to demonstrate the suppression of turbulence by negative sensible heat fluxes during the period in question.

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