The Spatiotemporal Evolution of the Diurnal Cycle in Two WRF Simulations of Tropical Cyclones

2022 ◽  
Keyword(s):  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Early Morning ◽  
Empirical Orthogonal Functions ◽  
Maximum Height ◽  
Orthogonal Functions ◽  
Diurnal Variability ◽  
Realistic Simulation ◽  
Fourier Filtering

Abstract The properties of diurnal variability in tropical cyclones (TCs) and the mechanisms behind them remain an intriguing aspect of TC research. This study provides a comprehensive analysis of diurnal variability in two simulations of TCs to explore these mechanisms. One simulation is a well known Hurricane Nature Run, which is a realistic simulation of a TC produced using the Weather Research and Forecasting model (WRF). The other simulation is a realistic simulation produced using WRF of Hurricane Florence (2018) using hourly ERA5 reanalysis data as input. Empirical orthogonal functions and Fourier filtering are used to analyze diurnal variability in the TCs. In both simulations a diurnal squall forms at sunrise in the inner core and propagates radially outwards and intensifies until midday. At midday the upper-level outflow strengthens, surface inflow weakens, and the cirrus canopy reaches its maximum height and radial extent. At sunset and overnight, the surface inflow is stronger, and convection inside the RMW peaks. Therefore, two diurnal cycles of convection exist in the TCs with different phases of maxima: eyewall convection at sunset and at night, and rainband convection in the early morning. This study finds that the diurnal pulse in the cirrus canopy is not advectively-driven, nor can it be attributed to weaker inertial stability at night; rather, the results indicate direct solar heating as a mechanism for cirrus canopy lifting and enhanced daytime outflow. These results show a strong diurnal modulation of tropical cyclone structure, and are consistent with other recent observational and modeling studies of the TC diurnal cycle.

Idealized Numerical Modeling of the Diurnal Cycle of Tropical Cyclones

2016 ◽  
Vol 73 (10) ◽  
pp. 4189-4201 ◽  
Author(s):  
Erika L. Navarro ◽  
Gregory J. Hakim
Keyword(s):  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Random Noise ◽  
Early Morning ◽  
Latent Heating ◽  
Daily Cycle ◽  
Layer Composite ◽  
Late Evening

Abstract A numerical experiment is performed to evaluate the role of the daily cycle of radiation on axisymmetric hurricane structure. Although a diurnal response in high cloudiness has been well documented previously, the link to tropical cyclone (TC) structure and intensity remains unknown. Previous modeling studies attributed differences in results to experimental setup (e.g., initial and boundary conditions) as well as to radiative parameterizations. Here, a numerically simulated TC in a statistically steady state is examined for 300 days to quantify the TC response to the daily cycle of radiation. Fourier analysis in time reveals a spatially coherent diurnal signal in the temperature, wind, and latent heating tendency fields. This signal is statistically different from random noise and accounts for up to 62% of the variance in the TC outflow and 28% of the variance in the boundary layer. Composite analysis of each hour of the day reveals a cycle in storm intensity: a maximum is found in the morning and a minimum in the evening, with magnitudes near 1 m s−1. Anomalous latent heating forms near the inner core of the storm in the late evening, which persists throughout the early morning. Examination of the radial–vertical wind suggests two distinct circulations: 1) a radiatively driven circulation in the outflow layer due to absorption of solar radiation and 2) a convectively driven circulation in the lower and middle troposphere due to anomalous latent heating. These responses are coupled and are periodic with respect to the diurnal cycle.

scholarly journals Upper-Tropospheric Low Richardson Number in Tropical Cyclones: Sensitivity to Cyclone Intensity and the Diurnal Cycle

2016 ◽  
Vol 73 (2) ◽  
pp. 545-554 ◽  
Author(s):  
Patrick Duran ◽  
John Molinari
Keyword(s):  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Richardson Number ◽  
Vertical Wind Shear ◽  
Early Morning ◽  
Static Stability ◽  
Diurnal Variability ◽  
High Vertical Resolution ◽  
Tropical Depressions ◽  
Upper Level

Abstract High-vertical-resolution rawinsondes were used to document the existence of low–bulk Richardson number (Rb) layers in tropical cyclones. The largest frequency of low Rb existed in the inner 200 km at the 13.5-km level. This peak extended more than 1000 km from the storm center and sloped downward with radius. The presence of an extensive upper-tropospheric low-Rb layer supports the assumption of Richardson number criticality in tropical cyclone outflow by Emanuel and Rotunno. The low-Rb layers were found to be more common in hurricanes than in tropical depressions and tropical storms. This sensitivity to intensity was attributed to a reduction of upper-tropospheric static stability as tropical cyclones intensify. The causes of this destabilization include upper-level cooling that is related to an elevation of the tropopause in hurricanes and greater longwave radiative warming in the well-developed hurricane cirrus canopy. Decreased mean static stability makes the production of low Rb by gravity waves and other perturbations easier to attain. The mean static stability and vertical wind shear do not exhibit diurnal variability. There is some indication, however, that low Richardson numbers are more common in the early morning than in the early evening, especially near the 200–300-km radius. The location and timing of this diurnal variability is consistent with previous studies that found a diurnal cycle of infrared brightness temperature and rainfall in tropical cyclones.

Cloud Properties and Their Seasonal and Diurnal Variability from TOVS Path-B

2006 ◽  
Vol 19 (21) ◽  
pp. 5531-5553 ◽  
Author(s):  
C. J. Stubenrauch ◽  
A. Chédin ◽  
G. Rädel ◽  
N. A. Scott ◽  
S. Serrar
Keyword(s):  
South America ◽  
Diurnal Cycle ◽  
Cloud Amount ◽  
Early Morning ◽  
Infrared Observation ◽  
Relevant Variable ◽  
Diurnal Variability ◽  
Cloud Properties ◽  
Early Afternoon ◽  
The Tropics

Abstract Eight years of cloud properties retrieved from Television Infrared Observation Satellite-N (TIROS-N) Observational Vertical Sounder (TOVS) observations aboard the NOAA polar orbiting satellites are presented. The relatively high spectral resolution of these instruments in the infrared allows especially reliable cirrus identification day and night. This dataset therefore provides complementary information to the International Satellite Cloud Climatology Project (ISCCP). According to this dataset, cirrus clouds cover about 27% of the earth and 45% of the Tropics, whereas ISCCP reports 19% and 25%, respectively. Both global datasets agree within 5% on the amount of single-layer low clouds, at 30%. From 1987 to 1995, global cloud amounts remained stable to within 2%. The seasonal cycle of cloud amount is in general stronger than its diurnal cycle and it is stronger than the one of effective cloud amount, the latter the relevant variable for radiative transfer. Maximum effective low cloud amount over ocean occurs in winter in SH subtropics in the early morning hours and in NH midlatitudes without diurnal cycle. Over land in winter the maximum is in the early afternoon, accompanied in the midlatitudes by thin cirrus. Over tropical land and in the other regions in summer, the maximum of mesoscale high opaque clouds occurs in the evening. Cirrus also increases during the afternoon and persists during night and early morning. The maximum of thin cirrus is in the early afternoon, then decreases slowly while cirrus and high opaque clouds increase. TOVS extends information of ISCCP during night, indicating that high cloudiness, increasing during the afternoon, persists longer during night in the Tropics and subtropics than in midlatitudes. A comparison of seasonal and diurnal cycle of high cloud amount between South America, Africa, and Indonesia during boreal winter has shown strong similarities between the two land regions, whereas the Indonesian islands show a seasonal and diurnal behavior strongly influenced by the surrounding ocean. Deeper precipitation systems over Africa than over South America do not seem to be directly reflected in the horizontal coverage and mesoscale effective emissivity of high clouds.

scholarly journals Diurnal Cycle of Rainfall Associated with Landfalling Tropical Cyclones in China from Rain Gauge Observations

2017 ◽  
Vol 56 (9) ◽  
pp. 2595-2605 ◽  
Author(s):  
Hao Hu ◽  
Yihong Duan ◽  
Yuqing Wang ◽  
Xinghai Zhang
Keyword(s):  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Rain Rate ◽  
Inner Core ◽  
Outer Region ◽  
Rain Gauge ◽  
Core Region ◽  
The Core ◽  
Storm Center ◽  
Landfalling Tropical Cyclones

AbstractThe diurnal variation of rainfall over China associated with landfalling tropical cyclones (TCs) is investigated using hourly rain gauge observations obtained from 2425 conventional meteorological stations in China. Records between 12 h prior to landfall and 12 h after landfall of 450 landfalling TCs in China from 1957 to 2014 are selected as samples. The harmonic analysis shows an obvious diurnal signal in TC rainfall with a rain-rate peak in the early morning and a minimum in the afternoon. The diurnal cycle in the outer region (between 400- and 900-km radii from the storm center) is found to be larger than in the core region (within 400 km of the storm center). This could be attributed to the effect of land on the inner core of the storms as the diurnal cycle is distinct in the core region well before landfall. As the result of this diurnal cycle, TCs making landfall at night tend to have cumulative precipitation, defined as the precipitation cumulated from the time at landfall to 12 h after landfall, about 30% larger than those making landfall around noon or afternoon. Moreover, the radial propagation of the diurnal cycle in TC rain rate, which has been a controversial phenomenon in some previous studies with remote sensing observations, was not present in this study that is based on rain gauge observations. Results also show that the diurnal signal has little dependence on the storm intensity 12 h prior to landfall.

Diurnal Variations in Rainfall and Precipitation Asymmetry of Tropical Cyclones in the Northwest Pacific Region

2021 ◽  
pp. 1-52
Author(s):  
Xinyan Zhang ◽  
Weixin Xu
Keyword(s):  
Diurnal Cycle ◽  
Radial Distance ◽  
Vertical Wind Shear ◽  
Early Morning ◽  
Diurnal Variations ◽  
Precipitation Intensity ◽  
Northwest Pacific ◽  
Diurnal Changes ◽  
Precipitation Frequency ◽  
Diurnal Variability

AbstractThis study investigates diurnal variations of tropical cyclone precipitation in the northwest Pacific (NWP) region, including the South China Sea (SCS) and adjacent landmasses. Diurnal cycles of TC rainfall show significant land-sea contrasts. The primary peak of (unconditional) mean TC rain rate occurs in the early morning (06 LT) and the afternoon (15 LT) over the ocean and land, respectively. Both the total and heavy TC precipitation extend further inland in the afternoon, while nocturnal heavy TC rain is more confined to the coast. A significant semidiurnal cycle of TC precipitation is observed over the ocean, i.e., a secondary peak near 18 LT. The diurnal cycle of TC rainfall also depends on precipitation frequency, intensity, and radial distance from the TC center. Over the ocean, though TC precipitation intensity shows a pronounced diurnal cycle, its precipitation frequency exhibits virtually no diurnal variation. Over land, TC precipitation frequency markedly peaks in the afternoon (15 LT), while its precipitation intensity interestingly maximizes in the early morning (03-06 LT). Diurnal variations of TC asymmetric rainfall structure are consistent with diurnal changes of vertical wind shear. Over the SCS, maximum precipitation located in the downshear-left quadrant and is the most extensive in the morning. However, this heavy rain area shrinks and shifts downshear-ward in the afternoon, consistent with changes of the magnitude (reduced) and direction (clockwise) of shear. In contrast, TCs over the open ocean of NWP (OWP) have little diurnal variability of precipitation asymmetry, due mainly to a diurnally invariant shear environment.

An Improved Statistical Scheme for the Prediction of Tropical Cyclones Making Landfall in South China

2010 ◽  
Vol 25 (2) ◽  
pp. 587-593 ◽  
Author(s):  
Andy Zung-Ching Goh ◽  
Johnny C. L. Chan
Keyword(s):  
South China Sea ◽  
Tropical Cyclones ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Empirical Orthogonal Functions ◽  
Annual Number ◽  
Orthogonal Functions ◽  
Factors Affecting ◽  
Using Data

Abstract This study describes an improved statistical scheme for predicting the annual number of tropical cyclones (TCs) making landfall along the coast of south China using data from 1965 to 2005. Based on the factors affecting TC behavior inside the South China Sea (SCS), those responsible for TCs making landfall are identified. Equations are then developed using the coefficients of empirical orthogonal functions of these factors to predict, in April, the number of these TCs in the early (May–August) and late (September–December) seasons, and in June, the number in the period between July to December. The new scheme achieves a forecast skill of 51% over climatology, or an improvement of about 11% compared to previous studies, when predicting landfalling TC for the whole season, and it seems to be able to capture the decrease in their number in the recent years. Analyses of the flow patterns suggest that the conditions inside the SCS are apparently the major factor affecting the number of landfalling TCs. In years in which this number is above normal, conditions inside the SCS are favorable for TC genesis, and vice versa. The strength of the 500-hPa subtropical high also seems to be a factor in determining whether TCs from the western North Pacific (WNP) could enter the SCS and make landfall.

scholarly journals Tropical Cyclone Diurnal Cycle as Observed by TRMM

2016 ◽  
Vol 144 (8) ◽  
pp. 2793-2808 ◽  
Author(s):  
Kenneth D. Leppert ◽  
Daniel J. Cecil
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Deep Layer ◽  
Tropical Rainfall Measuring Mission ◽  
Local Standard ◽  
Intensity Changes ◽  
Microwave Imager ◽  
Trmm Microwave Imager

Abstract Previous work has indicated a clear, consistent diurnal cycle in rainfall and cold cloudiness coverage around tropical cyclones. This cycle may have important implications for structure and intensity changes of these storms and the forecasting of such changes. The goal of this paper is to use passive and active microwave measurements from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR), respectively, to better understand the tropical cyclone diurnal cycle throughout a deep layer of a tropical cyclone’s clouds. The composite coverage by PR reflectivity ≥20 dBZ at various heights as a function of local standard time (LST) and radius suggests the presence of a diurnal signal for radii <500 km through a deep layer (2–10-km height) of the troposphere using 1998–2011 Atlantic tropical cyclones of at least tropical storm strength. The area covered by reflectivity ≥20 dBZ at radii 100–500 km peaks in the morning (0130–1030 LST) and reaches a minimum 1030–1930 LST. Radii between 300 and 500 km tend to reach a minimum in coverage closer to 1200 LST before reaching another peak at 2100 LST. The inner core (0–100 km) appears to be associated with a single-peaked diurnal cycle only at upper levels (8–10 km) with a maximum at 2230–0430 LST. The TMI rainfall composites suggest a clear diurnal cycle at all radii between 200 and 1000 km with peak rainfall coverage and rain rate occurring in the morning (0130–0730 LST).

Empirical Methods in Short-Term Climate Prediction

2006 ◽  
Author(s):  
Huug van den Dool
Keyword(s):  
Climate Prediction ◽  
Empirical Orthogonal Functions ◽  
Data Sets ◽  
Seasonal Forecasts ◽  
Short Term ◽  
Orthogonal Functions ◽  
Ocean Atmosphere Interaction ◽  
Global Coverage ◽  
Atmosphere Interaction ◽  
Global Data

This clear and accessible text describes the methods underlying short-term climate prediction at time scales of 2 weeks to a year. Although a difficult range to forecast accurately, there have been several important advances in the last ten years, most notably in understanding ocean-atmosphere interaction (El Nino for example), the release of global coverage data sets, and in prediction methods themselves. With an emphasis on the empirical approach, the text covers in detail empirical wave propagation, teleconnections, empirical orthogonal functions, and constructed analogue. It also provides a detailed description of nearly all methods used operationally in long-lead seasonal forecasts, with new examples and illustrations. The challenges of making a real time forecast are discussed, including protocol, format, and perceptions about users. Based where possible on global data sets, illustrations are not limited to the Northern Hemisphere, but include several examples from the Southern Hemisphere.

scholarly journals Spatio-Temporal Patterns of Mass Changes in Himalayan Glaciated Region from EOF Analyses of GRACE Data

2021 ◽  
Vol 13 (2) ◽  
pp. 265
Author(s):  
Harika Munagapati ◽  
Virendra M. Tiwari
Keyword(s):  
Temperature Anomaly ◽  
Mass Gain ◽  
Snow Accumulation ◽  
Empirical Orthogonal Functions ◽  
Total Water ◽  
Orthogonal Functions ◽  
Grace Data ◽  
Grace Satellite ◽  
Spatio Temporal ◽  
Gravity Recovery

The nature of hydrological seasonality over the Himalayan Glaciated Region (HGR) is complex due to varied precipitation patterns. The present study attempts to exemplify the spatio-temporal variation of hydrological mass over the HGR using time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellite for the period of 2002–2016 on seasonal and interannual timescales. The mass signal derived from GRACE data is decomposed using empirical orthogonal functions (EOFs), allowing us to identify the three broad divisions of HGR, i.e., western, central, and eastern, based on the seasonal mass gain or loss that corresponds to prevailing climatic changes. Further, causative relationships between climatic variables and the EOF decomposed signals are explored using the Granger causality algorithm. It appears that a causal relationship exists between total precipitation and total water storage from GRACE. EOF modes also indicate certain regional anomalies such as the Karakoram mass gain, which represents ongoing snow accumulation. Our causality result suggests that the excessive snowfall in 2005–2008 has initiated this mass gain. However, as our results indicate, despite the dampening of snowfall rates after 2008, mass has been steadily increasing in the Karakorum, which is attributed to the flattening of the temperature anomaly curve and subsequent lower melting after 2008.

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