Turbulence Variations in the Upper Troposphere in Tropical Cyclones from NOAA G-IV Flight-Level Vertical Acceleration Data

2019 ◽  
Vol 58 (3) ◽  
pp. 569-583
Author(s):  
John Molinari ◽  
Michaela Rosenmayer ◽  
David Vollaro ◽  
Sarah D. Ditchek
Keyword(s):  
Tropical Cyclones ◽  
Radiative Forcing ◽  
Vertical Acceleration ◽  
Unstable Region ◽  
Absolute Vorticity ◽  
Upper Troposphere ◽  
Hurricane Ivan ◽  
The North ◽  
Inertial Instability

AbstractThe NOAA G-IV aircraft routinely measures vertical aircraft acceleration from the inertial navigation system at 1 Hz. The data provide a measure of turbulence on a 250-m horizontal scale over a layer from 12.8- to 14.8-km elevation. Turbulence in this layer of tropical cyclones was largest by 35%–40% in the inner 200 km of radius and decreased monotonically outward to the 1000-km radius. Turbulence in major hurricanes exceeded that in weaker tropical cyclones. Turbulence data points were divided among three regions of the tropical cyclone: cirrus canopy; outside the cirrus canopy; and a transition zone between them. Without exception, turbulence was greater within the canopy and weaker outside the canopy. Nighttime turbulence exceeded daytime turbulence for all radii, especially within the cirrus canopy, implicating radiative forcing as a factor in turbulence generation. A case study of widespread turbulence in Hurricane Ivan (2004) showed that interactions between the hurricane outflow channel and westerlies to the north created a region of absolute vorticity of −6 × 10−5 s−1 in the upper troposphere. Outflow accelerated from the storm center into this inertially unstable region, and visible evidence for turbulence and transverse bands of cirrus appeared radially inward of the inertially unstable region. It is argued that both cloud-radiative forcing and the development of inertial instability within a narrow outflow layer were responsible for the turbulence. In contrast, a second case study (Isabel 2003) displayed strong near-core turbulence in the presence of large positive absolute vorticity and no local inertial instability. Peak turbulence occurred 100 km downwind of the eyewall convection.

scholarly journals Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

2016 ◽  
Author(s):  
M. Venkat Ratnam ◽  
S. Ravindra Babu ◽  
S. S. Das ◽  
Ghouse Basha ◽  
B. V. Krishnamurthy ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Lower Stratosphere ◽  
North Indian Ocean ◽  
Satellite Observations ◽  
Upper Troposphere ◽  
North West ◽  
The North ◽  
The Impact

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.

Symmetric Instability in the Outflow Layer of a Major Hurricane

2014 ◽  
Vol 71 (10) ◽  
pp. 3739-3746 ◽  
Author(s):  
John Molinari ◽  
David Vollaro
Keyword(s):  
Potential Temperature ◽  
Outer Edge ◽  
Unstable State ◽  
Upper Troposphere ◽  
Hurricane Ivan ◽  
Equivalent Potential ◽  
Inertial Instability ◽  
Major Hurricane ◽  
Cloudy Region ◽  
Symmetric Instability

Abstract A set of 327 dropsondes from the NOAA G-IV aircraft was used to create a composite analysis of the azimuthally averaged absolute angular momentum in the outflow layer of major Hurricane Ivan (2004). Inertial instability existed over a narrow layer in the upper troposphere between the 350- and 450-km radii. Isolines of potential and equivalent potential temperature showed that the conditions for both dry and moist symmetric instability were satisfied in the same region, but over a deeper layer from 9 to 12 km. The radial flow maximized at the outer edge of the unstable region. The symmetrically unstable state existed above a region of outward decrease of temperature between the cirrus overcast of the storm and clear air outside. It is hypothesized that the temperature gradient was created as a result of longwave heating within the cirrus overcast and longwave cooling outside the cloudy region. This produced isentropes that sloped upward with radius in the same region that absolute momentum surfaces were flat or sloping downward, thus creating symmetric instability. Although this instability typically follows rather than precedes intensification, limited numerical evidence suggests that the reestablishment of a symmetrically neutral state might influence the length of the intensification period.

scholarly journals Influence of Saharan dust on Atlantic tropical cyclones

2020 ◽  
Author(s):  
Zhenxi Zhang ◽  
Wen Zhou
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Saharan Dust ◽  
Tropical Atlantic ◽  
Atmospheric Moisture ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Itcz ◽  
Atlantic Tropical Cyclone

Abstract. The influence of Saharan dust outbreaks on summertime Atlantic tropical cyclone (TC) activity is explored using continuous atmospheric reanalysis products and TC track data from 1980 to 2019. Analyses reveal that the Saharan dust plume over the tropical Atlantic can affect TC activity by affecting the atmospheric hydrology and radiation absorbed by the earth's surface, which can be classified into three mechanisms. (1) A strong Saharan dust plume indirectly induces the reduction of atmospheric moisture, which further suppresses TC track, number of TC days, and intensity, with the influence covering the whole tropical Atlantic. (2) A strong Saharan dust plume enhances atmospheric moisture just along the North Atlantic ITCZ through the dust microphysical effect, which further promotes TC activity along 10º N latitude in June. (3) The climatological influence of dust on TC activity is caused by the strong radiative forcing of Saharan dust over the eastern tropical Atlantic in June, which produces an evident reduction in SST and lessens the duration and intensity of regional TC activity in June, according to the 40-yr average from 1980 to 2019.

Forecasting Challenges Associated with Tropical Cyclones within Subtropical Gyres

2014 ◽  
Vol 29 (1) ◽  
pp. 99-114 ◽  
Author(s):  
Brian Crandall ◽  
John Molinari ◽  
David Vollaro
Keyword(s):  
Tropical Cyclones ◽  
Tropical Storm ◽  
Temperature Gradients ◽  
Subtropical Gyre ◽  
Northwest Pacific ◽  
The North ◽  
History Of ◽  
Joint Typhoon Warning Center

Abstract This case study examines the complex history of a tropical storm that formed southeast of a large subtropical gyre. In real time the tropical storm was incorrectly identified as being two separate storms, and at one time was mislocated by 465 km. The unique forecast problems associated with tropical cyclones within a subtropical gyre are described. The tropical storm propagated around the gyre and encountered a midlevel temperature gradient to the north. The interaction of the storm with this gradient produced a strong midtropospheric temperature dipole. Temperature advection within this feature produced a change in structure to a subtropical storm corotating with an upper low. The subtropical storm turned equatorward and nearly came to a halt as the upper low became aligned with the storm. As convection increased over warm water, the upper low shifted away from the center and the storm reversed direction and moved poleward. These sudden track changes have frequently been observed in the northwest Pacific, but the role of midtropospheric temperature gradients has not previously been addressed. Clear air at the gyre center coincided with a region of cold advection. A fishhook structure in the gyre cloudiness developed as a result of warm advection east and north of the gyre. The subtropical structure of the storm evolved within the fishhook. It is recommended that the Joint Typhoon Warning Center (JTWC) provide formal warnings on subtropical storms, because their baroclinic nature can produce dramatic track changes associated with the presence of upper lows near the center.

Low Richardson Number in the Tropical Cyclone Outflow Layer

2014 ◽  
Vol 71 (9) ◽  
pp. 3164-3179 ◽  
Author(s):  
John Molinari ◽  
Patrick Duran ◽  
David Vollaro
Keyword(s):  
Tropical Cyclones ◽  
Vertical Wind Shear ◽  
Static Stability ◽  
Cloud Base ◽  
Flux Divergence ◽  
Sharp Transition ◽  
Turbulent Layer ◽  
Upper Troposphere ◽  
Hurricane Ivan ◽  
Major Hurricane

Abstract Dropsondes from the NOAA G-IV aircraft were used to examine the presence of low bulk Richardson numbers RB in tropical cyclones. At least one 400-m layer above z = 7.5 km exhibited RB < 1 in 96% of the sondes and RB ≤ 0.25 in 35% of the sondes. The latter represent almost certain turbulence. Sondes from major Hurricane Ivan (2004) were examined in detail. Turbulent layers fell into three broad groups. The first was found below cloud base near the edge of the central dense overcast (CDO) where relative humidity fell below 40%. Near-zero static stability existed within the turbulent layer with stability and shear maxima above it. This structure strongly resembled that seen previously from sublimation of precipitation beneath cloud base. The second type of turbulent layer was located within CDO clouds in the upper troposphere and was due almost entirely to near-zero static stability. This most likely arose as a result of cooling via longwave flux divergence below CDO top. The third type of turbulent layer existed well outside the CDO and was produced by large local vertical wind shear. The shear maxima associated with the beneath-cloud and outside-CDO turbulent layers produced a sharp transition from weak inflow below to strong outflow above. The results suggest that the CDO creates its own distinctive stability profile that strongly influences the distribution of turbulence and the transition to outflow in tropical cyclones.

scholarly journals Investigating Global Tropical Cyclone Activity with a Hierarchy of AGCMs: The Role of Model Resolution

2013 ◽  
Vol 26 (1) ◽  
pp. 133-152 ◽  
Author(s):  
Jane Strachan ◽  
Pier Luigi Vidale ◽  
Kevin Hodges ◽  
Malcolm Roberts ◽  
Marie-Estelle Demory
Keyword(s):  
Tropical Cyclone ◽  
Interannual Variability ◽  
Tropical Cyclones ◽  
Tropical Cyclone Activity ◽  
Model Resolution ◽  
Cyclone Activity ◽  
Absolute Vorticity ◽  
Low Level ◽  
The North ◽  
The Impact

Abstract The ability to run general circulation models (GCMs) at ever-higher horizontal resolutions has meant that tropical cyclone simulations are increasingly credible. A hierarchy of atmosphere-only GCMs, based on the Hadley Centre Global Environmental Model version 1 (HadGEM1) with horizontal resolution increasing from approximately 270 to 60 km at 50°N, is used to systematically investigate the impact of spatial resolution on the simulation of global tropical cyclone activity, independent of model formulation. Tropical cyclones are extracted from ensemble simulations and reanalyses of comparable resolutions using a feature-tracking algorithm. Resolution is critical for simulating storm intensity and convergence to observed storm intensities is not achieved with the model hierarchy. Resolution is less critical for simulating the annual number of tropical cyclones and their geographical distribution, which are well captured at resolutions of 135 km or higher, particularly for Northern Hemisphere basins. Simulating the interannual variability of storm occurrence requires resolutions of 100 km or higher; however, the level of skill is basin dependent. Higher resolution GCMs are increasingly able to capture the interannual variability of the large-scale environmental conditions that contribute to tropical cyclogenesis. Different environmental factors contribute to the interannual variability of tropical cyclones in the different basins: in the North Atlantic basin the vertical wind shear, potential intensity, and low-level absolute vorticity are dominant, whereas in the North Pacific basins midlevel relative humidity and low-level absolute vorticity are dominant. Model resolution is crucial for a realistic simulation of tropical cyclone behavior, and high-resolution GCMs are found to be valuable tools for investigating the global location and frequency of tropical cyclones.

scholarly journals Rapid convective outflow from the U.S. to the upper troposphere over the North Atlantic during the NASA INTEX-NA airborne campaign: flight 13 case study

2007 ◽  
Vol 7 (6) ◽  
pp. 17367-17400
Author(s):  
S. Y. Kim ◽  
R. Talbot ◽  
H. Mao ◽  
D. Blake ◽  
S. Vay ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
The United States ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The North ◽  
Synoptic Conditions ◽  
The North Atlantic ◽  
The U.S

Abstract. A case study of convective outflow from the United States (U.S.) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influence was evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of fast transport via convective uplifting of boundary layer air over the southeastern U.S. This mechanism is supported by the similar slopes values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern U.S. In addition, the aircraft measurements suggest that outflow from the U.S. augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of U.S. anthropogenic emissions on the troposphere over the North Atlantic.

scholarly journals Measurements of Overwater Gust Factor from Near Surface to Beyond Common Hub Height: A Case Study

2020 ◽  
Vol 03 (03) ◽  
pp. 1-1
Author(s):  
Shih-Ang Hsu ◽  
Keyword(s):  
Gulf Of Mexico ◽  
Tropical Cyclones ◽  
Atmospheric Stability ◽  
Sea Surface ◽  
Offshore Wind ◽  
Near Surface ◽  
North Central ◽  
Gust Factor ◽  
The North

In September 2020 Hurricane Sally affected the north central Gulf of Mexico. Making use of the anemometers data available at 4 oil rigs over the affected region, it is found that, when the atmospheric stability was near-neutral, the gust factor (G) decreases linearly with height from approximately 1.28 at 35m above the sea surface to 1.18 at 160 m. In other words, G decreases linearly at the rate around 8% per 100 m from the typical hub height to beyond common hub height. Based on the linear equation found in this study, the G extrapolated to the standard height of 10 m is approximately 1.3 which is also consistent with that measured at two buoys over the affected region. Therefore, a G of 1.3 at near surface may be useful for offshore wind energy R&D and O&M, particularly for those regions affected by tropical cyclones.

scholarly journals Effect of tropical cyclones on the stratosphere–troposphere exchange observed using satellite observations over the north Indian Ocean

2016 ◽  
Vol 16 (13) ◽  
pp. 8581-8591 ◽  
Author(s):  
M. Venkat Ratnam ◽  
S. Ravindra Babu ◽  
S. S. Das ◽  
G. Basha ◽  
B. V. Krishnamurthy ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Water Vapour ◽  
Tropical Cyclones ◽  
Lower Stratosphere ◽  
North Indian Ocean ◽  
Satellite Observations ◽  
Upper Troposphere ◽  
The North ◽  
The Impact ◽  
Cyclonic Storms

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere–troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the north Indian Ocean during 2007–2013 on the STE processes is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) radio occultation (RO) measurements, and ozone and water vapour concentrations in the UTLS region are obtained from Aura Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km of the centre of the tropical cyclone. In our earlier study, we observed a decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K), and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within 500 km of the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from the cyclone centre, whereas the enhancement in the water vapour in the lower stratosphere is more significant on the south-east side, extending from 500 to 1000 km away from the cyclone centre. The cross-tropopause mass flux for different intensities of cyclones is estimated and it is found that the mean flux from the stratosphere to the troposphere for cyclonic storms is 0.05 ± 0.29 × 10−3 kg m−2, and for very severe cyclonic storms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed on the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget, and consequentially the STE in the UTLS region.

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