scholarly journals An Observational Study of the Diurnal Variation of Precipitation over Hong Kong and the Underlying Processes

2018 ◽  
Vol 57 (6) ◽  
pp. 1385-1402 ◽  
Author(s):  
Xiuzhen Li ◽  
Ngar-Cheung Lau ◽  
Tsz-Cheung Lee
Keyword(s):  
Hong Kong ◽  
Diurnal Variation ◽  
Diurnal Cycle ◽  
Radiative Cooling ◽  
Land Breeze ◽  
Thermal Contrast ◽  
Near Surface ◽  
Southeast China ◽  
Hourly Rainfall ◽  
Weak Divergence

AbstractHourly rainfall from automatic weather stations and reanalysis data from MERRA-2 are used to investigate the diurnal variation of precipitation in Hong Kong, a site along the southeast China coast with strong interactions between the monsoonal circulation and the land–sea breeze. The precipitation in Hong Kong is characterized by a spatially uniform diurnal cycle with the peak at about 0800 local time (LT), with rather weak dependence on local terrain. Precipitation unrelated to tropical cyclones (TCs) dominates the diurnal variation of precipitation, especially in the summer. The diurnal cycle exhibits a notable seasonal dependence, with the strongest signal in the summer. The morning peak of precipitation over Hong Kong is coincident with deep rising motion, linking to near-surface convergence and overlying weak divergence. The convergence may be attributed to the prevalence of the southerly monsoonal flow over the South China Sea (SCS) and to the northerly land breeze induced by the land–sea thermal contrast in the morning. The overlying weak divergence could be ascribed to the nocturnal–early morning acceleration of southerly flow over southeast China. Linked to the inverse relationship between monsoon intensity and the land–sea thermal contrast, the diurnal cycle of precipitation is strengthened when the SCS monsoon is active and weakened when the land–sea thermal contrast is high. Both the cloud-top radiative cooling effect and the enhanced radiative cooling over inland cloud-free areas also play roles in the development of the morning rainfall peak over Hong Kong.

scholarly journals Extent of diurnal cycle of rainfall and its intra seasonal variation over coastal Tamil Nadu during north east monsoon season

MAUSAM ◽  
2022 ◽  
Vol 73 (1) ◽  
pp. 1-18
Author(s):  
Y.E.A. RAJ ◽  
B. AMUDHA
Keyword(s):  
Diurnal Variation ◽  
Diurnal Cycle ◽  
Tamil Nadu ◽  
Monsoon Season ◽  
Statistical Significance ◽  
Early Morning ◽  
Rainfall Anomaly ◽  
Land Breeze ◽  
North East ◽  
Hourly Rainfall

The diurnal variation of north east monsoon rainfall of coastal Tamil Nadu represented by four coastal stations Chennai Nungambakkam (Nbk), Chennai Meenambakkam (Mbk), Nagapattinam (Npt) and Pamban (Pbn)  was  studied in detail based on hourly rainfall data of rainy days only, for the period 1 Oct-31 Dec for the 47/48  year period 1969-2016/2017.  Mean Octet rainfall and its anomaly were computed for the 8 octets  00-03,…., 21-24 hrs of the day and the anomaly was tested for statistical significance. Various analysis for the individual months of Oct, Nov, Dec and the entire period Oct-Dec were separately conducted.  The basic technique of evolutionary histogram analysis supplemented by harmonic analysis of octet mean rainfall anomaly was used to detect the diurnal cycle signal. Two indices  named as  diurnal variation of  rainfall index and coefficient of mean absolute octet rainfall anomaly representing the intensity of diurnal variation  in dimensionless numbers were defined,  computed  and interpreted. The analysis based on the above techniques revealed that the diurnal signal which shows an early morning maximum and late afternoon minimum of octet rainfall is well defined in Oct, decreases in Nov and further decreases in Dec for all the 4 stations. Though the diurnal variation manifests a well defined pattern in Dec the signal is not statistically significant in most cases. For Nbk and Mbk there is a weak secondary peak of octet rainfall anomaly occurring in the forenoon and afternoon respectively in Oct and Dec suggesting the presence of semi-diurnal variation of rainfall. Stationwise, the diurnal signal is most well defined for each month/season in Pbn followed by Npt, Nbk and then Mbk.   The physical causes behind the diurnal signal and its decrease as the north east monsoon season advances from Oct to Dec have been deliberated. The well known feature of nocturnal maximum of oceanic convection influencing a coastal station with maritime climate and the higher saturation at the lower levels of the upper atmosphere in the early morning hours have been advanced as some of the causes. For the much more complex feature of decrease of diurnal signal with the  advancement of the season, the decrease of minimum surface temperature over coastal Tamil Nadu from Oct to Dec causing an early morning conceptual land breeze has been shown as one of the plausible causes  based on analysis of temperature and wind.  Scope for further work based on data from automatic weather stations, weather satellites and Doppler Weather Radars has been discussed.

scholarly journals The influence of sea- and land-breeze circulations on the diurnal variability of precipitation over a tropical island

2017 ◽  
Author(s):  
Lei Zhu ◽  
Zhiyong Meng ◽  
Fuqing Zhang ◽  
Paul M. Markowski
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Diurnal Cycle ◽  
Lower Troposphere ◽  
Sea Breeze ◽  
Hainan Island ◽  
Dominant Factor ◽  
Land Breeze ◽  
Moist Convection ◽  
Diurnal Variability

Abstract. This study examines the diurnal variation of precipitation over Hainan Island in the South China Sea using gauge observations from 1950 to 2010 and CMORPH satellite estimates from 2006 to 2015, as well as numerical simulations. Precipitation is most significant from April to October, and exhibits a strong diurnal cycle resulting from land/sea breeze circulations. More than 60 % of the total annual precipitation over the island is attributable to the diurnal cycle, with a significant monthly variability as well. The CMORPH and gauge datasets agree well, except that the CMORPH data underestimates precipitation and has a 1-h delay of peaks. The diurnal cycle of the rainfall and the related land/sea breeze circulations during May and June were well captured by convection-allowing numerical simulations with WRF, which were initiated from 10-year average ERA-interim reanalysis, despite slightly overall overestimation and 1-h delay of the rainfall peak. The diurnal precipitation is due to a diurnal cycle of moist convection, which initiates around noontime owing to low-level convergence associated with the sea breeze circulation. The precipitation intensifies rapidly thereafter and peaks in the afternoon with the collisions of sea breeze fronts from different sides of the island. Cold pools of the convective storms contribute to the inland propagation of the sea breeze. The precipitation dissipates quickly in the evening owing to the cooling and stabilization of the lower troposphere and decrease of boundary-layer moisture. Interestingly, the rather high island orography is not a dominant factor in the diurnal variation of the precipitation over the island.

scholarly journals The influence of sea- and land-breeze circulations on the diurnal variability in precipitation over a tropical island

2017 ◽  
Vol 17 (21) ◽  
pp. 13213-13232 ◽  
Author(s):  
Lei Zhu ◽  
Zhiyong Meng ◽  
Fuqing Zhang ◽  
Paul M. Markowski
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Diurnal Cycle ◽  
Wrf Model ◽  
Lower Troposphere ◽  
Sea Breeze ◽  
Dominant Factor ◽  
Land Breeze ◽  
Moist Convection ◽  
Diurnal Variability

Abstract. This study examines the diurnal variation in precipitation over Hainan Island in the South China Sea using gauge observations from 1951 to 2012 and Climate Prediction Center MORPHing technique (CMORPH) satellite estimates from 2006 to 2015, as well as numerical simulations. The simulations are the first to use climatological mean initial and lateral boundary conditions to study the dynamic and thermodynamic processes (and the impacts of land–sea breeze circulations) that control the rainfall distribution and climatology. Precipitation is most significant from April to October and exhibits a strong diurnal cycle resulting from land–sea breeze circulations. More than 60 % of the total annual precipitation over the island is attributable to the diurnal cycle with a significant monthly variability. The CMORPH and gauge datasets agree well, except that the CMORPH data underestimate precipitation and have a 1 h peak delay. The diurnal cycle of the rainfall and the related land–sea breeze circulations during May and June were well captured by convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model, which were initiated from a 10-year average ERA-Interim reanalysis. The simulations have a slight overestimation of rainfall amounts and a 1 h delay in peak rainfall time. The diurnal cycle of precipitation is driven by the occurrence of moist convection around noontime owing to low-level convergence associated with the sea-breeze circulations. The precipitation intensifies rapidly thereafter and peaks in the afternoon with the collisions of sea-breeze fronts from different sides of the island. Cold pools of the convective storms contribute to the inland propagation of the sea breeze. Generally, precipitation dissipates quickly in the evening due to the cooling and stabilization of the lower troposphere and decrease of boundary layer moisture. Interestingly, the rather high island orography is not a dominant factor in the diurnal variation in precipitation over the island.

scholarly journals Characterizing the diurnal cycle of South Atlantic stratocumulus cloud properties from satellite retrievals

2018 ◽  
Author(s):  
Chellappan Seethala ◽  
Jan Fokke Meirink ◽  
Ákos Horváth ◽  
Ralf Bennartz ◽  
Rob Roebeling
Keyword(s):  
Diurnal Variation ◽  
Biomass Burning ◽  
Diurnal Cycle ◽  
Near Infrared ◽  
South Atlantic ◽  
Radiation Budget ◽  
Ozone Monitoring Instrument ◽  
Liquid Water Path ◽  
Diurnal Variability ◽  
Late Afternoon

Abstract. Marine stratocumulus (Sc) clouds play an essential role in the earth radiation budget. Here, we compare liquid water path (LWP), optical thickness (COT), and effective radius (CER) retrievals from two years of collocated Spinning Enhanced Visible and InfraRed Imager (SEVIRI), MODerate resolution Imaging Spectroradiometer (MODIS), and Tropical Rainfall Measuring Mission Microwave Imager (TMI) observations, estimate the effect of biomass burning smoke on passive imager retrievals, as well as evaluate the diurnal cycle of South Atlantic marine Sc clouds. The effect of absorbing aerosols from biomass burning on the retrievals was investigated using aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI). SEVIRI and MODIS LWPs were found to decrease with increasing AI relative to TMI LWP, consistent with well-known negative visible/near-infrared retrieval biases in COT and CER. In the aerosol-affected months of July–August–September, SEVIRI LWP – based on the 1.6-µm CER – was biased low by 14 g m−2 (~ 16 %) compared to TMI in overcast scenes, while MODIS LWP showed a smaller low bias of 4 g m−2 (~ 5 %) for the 1.6-µm channel and a high bias of 8 g m−2 (~ 10 %) for the 3.7-µm channel compared to TMI. Neglecting aerosol-affected pixels reduced the mean SEVIRI-TMI LWP bias considerably. On a two-year data base, SEVIRI LWP had a correlation with TMI and MODIS LWP of about 0.86 and 0.94, respectively, and biases of only 4–8 g m−2 (5–10 %) for overcast cases. The SEVIRI LWP diurnal cycle was in good overall agreement with TMI except in the aerosol-affected months. Both TMI and SEVIRI LWP decreased from morning to late afternoon, after which a slight increase was observed. Terra and Aqua MODIS mean LWPs also suggested a similar diurnal variation. The relative amplitude of the two-year mean and seasonal mean LWP diurnal cycle varied between 35–40 % from morning to late afternoon for overcast cases. The diurnal variation in SEVIRI LWP was mainly due to changes in COT, while CER showed only little diurnal variability.

Quantifying heating biases in marine air temperature observations, ~1790 - present

2021 ◽  
Author(s):  
Thomas Cropper ◽  
Elizabeth Kent ◽  
David Berry ◽  
Richard Cornes ◽  
Beatriz Recinos-Rivas
Keyword(s):  
Air Temperature ◽  
Diurnal Cycle ◽  
Surface Air Temperature ◽  
Night Time ◽  
Data Set ◽  
Near Surface ◽  
Marine Surface ◽  
Heating Model ◽  
Marine Air

<p>Accurate, long-term time series of near-surface air temperature (AT) are the fundamental datasets on which the magnitude of anthropogenic climate change is scientifically and societally addressed. Across the ocean, these (near-surface) climate records use Sea Surface Temperature (SST) instead of Marine Air Temperature (MAT) and blend the SST and AT over land to create datasets. MAT has often been overlooked as a data choice as daytime MAT observations from ships are known to contain warm biases due to the storage of accumulated solar energy. Two recent MAT datasets, CLASSnmat (1881 – 2019) and UAHNMAT (1900 – 2018), both use night-time MAT observations only. Daytime MAT observations in the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) account for over half of the MAT observations in ICOADS, and this proportion increases further back in time (i.e. pre-1850s). If long-term MAT records over the ocean are to be extended, the use of daytime MAT is vital.</p><p> </p><p>To adjust for the daytime MAT heating bias, and apply it to ICOADS, we present the application of a physics-based model, which accounts for the accumulated energy storage throughout the day. As the ‘true’ diurnal cycle of MAT over the ocean has not been, to-date, adequately quantified, our approach also removes the diurnal cycle from ICOADS observations and generates a night-time equivalent MAT for all observations. We fit this model to MAT observations from groups of ships in ICOADS that share similar heating biases and metadata characteristics. This enables us to use the empirically derived coefficients (representing the physical energy transfer terms of the heating model) obtained from the fit for use in removal of the heating bias and diurnal cycle from ship-based MAT observations throughout ICOADS which share similar characteristics (i.e. we can remove the diurnal cycle from a ship which only reports once daily at noon). This adjustment will create an MAT record of night-time-equivalent temperatures that will enable an extension of the marine surface AT record back into the 18<sup>th</sup> century.</p>

scholarly journals The Diurnal Variations of GPS PWV near Poyang Lake in China during Midsummer

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Shanshan Wu ◽  
Haibo Zou ◽  
Junjie Wu
Keyword(s):  
Diurnal Variation ◽  
Global Positioning System ◽  
Diurnal Cycle ◽  
Poyang Lake ◽  
Precipitable Water ◽  
Diurnal Variations ◽  
Diurnal Cycles ◽  
Global Positioning ◽  
Variance Contribution ◽  
Gps Observation

With the 1 h-averaged data of atmospheric precipitable water vapor (PWV) for 2015–2018 retrieved from 18 ground-based Global Positioning System (GPS) observation stations near Poyang Lake (PL), China, the diurnal variations of the PWV during midsummer (July-August) are studied by the harmonic method. Results show that significant diurnal variations of PWV are found at the 18 GPS stations. The harmonics with 24 h cycle (diurnal cycle) over PL (i.e., Duchang and Poyang) and Nanchang city only have about 50% (or even smaller than 50%) of variance contribution with the amplitude of about 0.2 mm, while above 70% (or even 80%) of variance contribution occurs elsewhere around PL, with the amplitude of about 0.9 mm. The harmonics with diurnal cycles in most stations peak from afternoon to evening (i.e., 1200-2000 LST), but one exception is Duchang site, where the diurnal cycle peaks in the morning (i.e., 1000 LST). Moreover, the harmonics with 12 h cycle (semidiurnal cycle) have the relatively uniform amplitude of about 0.2 mm, but their variance contributions show uneven distribution, with the contributions of about or above 50% in PL and Nanchang city (the semidiurnal cycles peak about 0000 LST or 1200 LST) and below 30% (or even 10%) in other areas. The preliminary diagnosis analysis shows that the diurnal variation of the low-level (below 850 hPa) air temperature (increasing after the sunrise, decreasing after the sunset, and peaking around 1400-1800 LST) may be responsible for the diurnal cycle. Moreover, in PL (Duchang and Poyang) and Nanchang city, the effects (heating or cooling) of lake and urban, the diurnal variation of the 10 m wind over PL, and the acceleration of PL on overlying air also contributed to the diurnal variation of PWV.

Diurnal and Seasonal Lightning Variability over the Gulf Stream and the Gulf of Mexico

2015 ◽  
Vol 72 (7) ◽  
pp. 2657-2665 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace ◽  
Michael L. Hutchins ◽  
Robert H. Holzworth
Keyword(s):  
Gulf Of Mexico ◽  
Diurnal Cycle ◽  
Gulf Stream ◽  
Land Surface ◽  
Southeastern United States ◽  
Surface Wind ◽  
Tropical Rainfall Measuring Mission ◽  
Sea Breeze ◽  
Near Surface ◽  
Early Evening

Recent observations from the World Wide Lightning Location Network (WWLLN) reveal a pronounced lightning maximum over the warm waters of the Gulf Stream that exhibits distinct diurnal and seasonal variability. Lightning is most frequent during summer (June–August). During afternoon and early evening, lightning is enhanced just onshore of the coast of the southeastern United States because of daytime heating of the land surface and the resulting sea-breeze circulations and convection. Near-surface wind observations from the Quick Scatterometer (QuikSCAT) satellite indicate divergence over the Gulf of Mexico and portions of the Gulf Stream at 1800 LT, at which time lightning activity is suppressed there. Lightning frequency exhibits a broad maximum over the Gulf Stream from evening through noon of the following day, and QuikSCAT wind observations at 0600 LT indicate low-level winds blowing away from the continent and converging over the Gulf Stream. Over the northern Gulf of Mexico, lightning is most frequent from around sunrise through late morning. During winter, lightning exhibits a weak diurnal cycle over the Gulf Stream, with most frequent lightning during the evening. Precipitation rates from a 3-hourly gridded dataset that incorporates observations from Tropical Rainfall Measuring Mission (TRMM), as well as other satellites, exhibit a diurnal cycle over the Gulf Stream that lags the lightning diurnal cycle by several hours.

scholarly journals Observation of Turbulent Mixing Characteristics in the Typical Daytime Cloud-Topped Boundary Layer over Hong Kong in 2019

2020 ◽  
Vol 12 (9) ◽  
pp. 1533 ◽  
Author(s):  
Tao Huang ◽  
Steve Hung-lam Yim ◽  
Yuanjian Yang ◽  
Olivia Shuk-ming Lee ◽  
David Hok-yin Lam ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Hong Kong ◽  
Vertical Velocity ◽  
Turbulent Mixing ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Surface Heating ◽  
Cloud Base ◽  
Radiative Cooling

Turbulent mixing is critical in affecting urban climate and air pollution. Nevertheless, our understanding of it, especially in a cloud-topped boundary layer (CTBL), remains limited. High-temporal resolution observations provide sufficient information of vertical velocity profiles, which is essential for turbulence studies in the atmospheric boundary layer (ABL). We conducted Doppler Light Detection and Ranging (LiDAR) measurements in 2019 using the 3-Dimensional Real-time Atmospheric Monitoring System (3DREAMS) to reveal the characteristics of typical daytime turbulent mixing processes in CTBL over Hong Kong. We assessed the contribution of cloud radiative cooling on turbulent mixing and determined the altitudinal dependence of the contribution of surface heating and vertical wind shear to turbulent mixing. Our results show that more downdrafts and updrafts in spring and autumn were observed and positively associated with seasonal cloud fraction. These results reveal that cloud radiative cooling was the main source of downdraft, which was also confirmed by our detailed case study of vertical velocity. Compared to winter and autumn, cloud base heights were lower in spring and summer. Cloud radiative cooling contributed ~32% to turbulent mixing even near the surface, although the contribution was relatively weaker compared to surface heating and vertical wind shear. Surface heating and vertical wind shear together contributed to ~45% of turbulent mixing near the surface, but wind shear can affect up to ~1100 m while surface heating can only reach ~450 m. Despite the fact that more research is still needed to further understand the processes, our findings provide useful references for local weather forecast and air quality studies.

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