scholarly journals Importance of vertical mixing and barrier layer variation on seasonal mixed layer heat balance in the Bay of Bengal

2017 ◽  
Author(s):  
Ullala Pathiranage Gayan Pathirana ◽  
Gengxin Chen ◽  
Tilak Priyadarshana ◽  
Dongxiao Wang
Keyword(s):  
Heat Flux ◽  
Mixed Layer ◽  
Barrier Layer ◽  
Bay Of Bengal ◽  
Heat Balance ◽  
Seasonal Cycle ◽  
Sensible Heat Flux ◽  
Vertical Mixing ◽  
Shortwave Radiation ◽  
Barrier Layer Thickness

Abstract. Time series measurements from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15° N, 90° E; 12° N, 90° E; 8° N, 90° E; 4° N, 90° E; 1.5° N, 90° E; 0° N, 90° E are used to investigate the seasonal mixed-layer heat balance and the importance of barrier layer thickness (BLT) and vertical mixing (Q−h) in the Bay of Bengal (BoB). It is found that the BLT, Q−h and mixed-layer heat balance all have a strong seasonality in the central BoB. Sea surface temperature (SST), salinity and wind are important for the observed strongest seasonal cycle of BLT in the central BoB, and wind is more important than the SST in the southern BoB. The heat storage rate (HSR) is primarily driven by latent heat flux and shortwave radiation (QSW and QL). Seasonal variations and the magnitudes of longwave radiation (QLW), sensible heat flux (QS), and horizontal mixed-layer heat advection are much weaker compared to those of QSW and QL. Q−h follows a pronounced seasonal cycle in the central BoB and is significantly positively correlated with the seasonal cycle of BLT at each mooring location. The seasonal variability of the stability favors the Q−h during winter and summer monsoon and suppress Q−h during monsoon transition periods. We found that Q−h plays the secondary role in the seasonal mixed-layer heat balance in the BoB. It is evident from the analysis that Q−h associated with temperature inversion (∆T) warms the mixed layer during winter and cools the mixed layer during summer. The warming tendency during winter is strong in the central BoB and weakens towards the equator, indicating a cooling tendency around the year. Our analysis further indicates the weakening of Q−h during monsoon transition periods favors the existence of warmer SST in the BoB, associated with thermal and salinity stratification in the central BoB.

scholarly journals Vertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

2019 ◽  
Vol 19 (10) ◽  
pp. 6949-6967 ◽  
Author(s):  
Linlin Wang ◽  
Junkai Liu ◽  
Zhiqiu Gao ◽  
Yubin Li ◽  
Meng Huang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Heat Storage ◽  
Sensible Heat Flux ◽  
Vertical Mixing ◽  
Shortwave Radiation ◽  
Sensible Heat ◽  
Wind Lidar ◽  
Attenuation Ratio ◽  
Pollution Episodes

Abstract. We investigated the interactions between the air pollutants and the structure of the urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325 m meteorological tower and a Doppler wind lidar during 1–4 December 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 5 %, 24 % and 63 % in afternoon hours (from 12:00 to 14:00 local standard time, LST) on 2–4 December, respectively, while for the net radiation (Rn) attenuation ratio at the 140 m level of the 325 m tower was 3 %, 27 % and 68 %. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140 m level, we found that the sensible heat flux was remarkably diminished during daytime on polluted days and even negative after sunrise (about 07:20 LST) till 14:00 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that vertical mixing was negatively related to the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) decreased about 44 % and 56 % on 2–3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 12:00 to 14:00 LST) were 44 (48) µg m−3 and 150 (120) µg m−3. Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

Impact of Barrier Layer Thickness on SST in the Central Tropical North Atlantic*

2009 ◽  
Vol 22 (2) ◽  
pp. 285-299 ◽  
Author(s):  
Gregory R. Foltz ◽  
Michael J. McPhaden
Keyword(s):  
Temperature Gradient ◽  
Layer Thickness ◽  
Mixed Layer ◽  
North Atlantic ◽  
Barrier Layer ◽  
Seasonal Cycle ◽  
Vertical Temperature Gradient ◽  
Vertical Temperature ◽  
Barrier Layer Thickness ◽  
Tropical North Atlantic

Abstract Measurements from three long-term moored buoys are used to investigate the impact of barrier layer thickness (BLT) on the seasonal cycle of sea surface temperature (SST) in the central tropical North Atlantic Ocean. It is found that seasonal variations of the BLT exert a considerable influence on SST through their modulation of the vertical heat flux at the base of the mixed layer, estimated as the residual in the mixed layer heat balance. Cooling associated with this term is strongest when the barrier layer is thin and the vertical temperature gradient at the base of the mixed layer is strong. Conversely, thick barrier layers are associated with a significant reduction in the vertical temperature gradient at the base of the mixed layer, which suppresses the upward transfer of cooler water into the mixed layer. Forced ocean and coupled ocean–atmosphere models that do not properly simulate the barrier layer may have difficulty reproducing the observed seasonal cycle of SST in the tropical North Atlantic.

scholarly journals Observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodes

2019 ◽  
Author(s):  
Linlin Wang ◽  
Junkai Liu ◽  
Zhiqiu Gao ◽  
Yubin Li ◽  
Meng Huang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Heat Storage ◽  
Sensible Heat Flux ◽  
Vertical Mixing ◽  
Shortwave Radiation ◽  
Sensible Heat ◽  
Wind Lidar ◽  
Attenuation Ratio ◽  
Pollution Episodes

Abstract. We investigated the interactions between the air pollutants and the structure of urban boundary layer (UBL) over Beijing by using the data mainly obtained from the 325-m meteorological tower and a Doppler wind lidar during 1–4 December, 2016. Results showed that the pollution episodes in this period could be characterized by low surface pressure, high relative humidity, weak wind, and temperature inversion. Compared with a clean daytime episode that took place on 1 December, results also showed that the attenuation ratio of downward shortwave radiation was about 4 %, 23 % and 78 % at 1200 local standard time (LST) on 2–4 December respectively, while for the net radiation (Rn) attenuation ratio at the 140-m level of the 325-m tower was 2 %, 24 %, and 86 %. The large reduction in Rn on 4 December was not only the result of the aerosols, but also clouds. Based on analysis of the surface energy balance at the 140-m level, we found that the sensible heat flux was remarkably diminished during daytimes on polluted days, and even negative after sunrise (about 0720 LST) till 1400 LST on 4 December. We also found that heat storage in the urban surface layer played an important role in the exchange of the sensible heat flux. Owing to the advantages of the wind lidar having superior spatial and temporal resolution, the vertical velocity variance could capture the evolution of the UBL well. It clearly showed that weak vertical mixing caused the concentrating of pollutants, and that vertical mixing would also be weakened by a certain quantity of pollutants, and then in turn worsened the pollution further. Compared to the clean daytime on 1 December, the maximums of the boundary layer height (BLH) reduced about 44 % and 56 % on 2–3 December, when the average PM2.5 (PM1) concentrations in afternoon hours (from 1200 to 1400 LST) were 44 (48) µg m−3 and 150 (120) µg m−3 . Part of these reductions of the BLH was also contributed by the effect of the heat storage in the urban canopy.

scholarly journals Seasonal Mixed Layer Heat Balance of the Southwestern Tropical Indian Ocean*

2010 ◽  
Vol 23 (4) ◽  
pp. 947-965 ◽  
Author(s):  
Gregory R. Foltz ◽  
Jérôme Vialard ◽  
B. Praveen Kumar ◽  
Michael J. McPhaden
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Heat Balance ◽  
Seasonal Cycle ◽  
Surface Wind ◽  
Tropical Indian Ocean ◽  
Surface Heat ◽  
Shortwave Radiation ◽  
Boreal Summer ◽  
Heat Advection

Abstract Sea surface temperature (SST) in the southwestern tropical Indian Ocean exerts a significant influence on global climate through its influence on the Indian summer monsoon and Northern Hemisphere atmospheric circulation. In this study, measurements from a long-term moored buoy are used in conjunction with satellite, in situ, and atmospheric reanalysis datasets to analyze the seasonal mixed layer heat balance in the thermocline ridge region of the southwestern tropical Indian Ocean. This region is characterized by a shallow mean thermocline (90 m, as measured by the 20°C isotherm) and pronounced seasonal cycles of Ekman pumping and SST (seasonal ranges of −0.1 to 0.6 m day−1 and 26°–29.5°C, respectively). It is found that surface heat fluxes and horizontal heat advection contribute significantly to the seasonal cycle of mixed layer heat storage. The net surface heat flux tends to warm the mixed layer throughout the year and is strongest during boreal fall and winter, when surface shortwave radiation is highest and latent heat loss is weakest. Horizontal heat advection provides warming during boreal summer and fall, when southwestward surface currents and horizontal SST gradients are strongest, and is close to zero during the remainder of the year. Vertical turbulent mixing, estimated as a residual in the heat balance, also undergoes a significant seasonal cycle. Cooling from this term is strongest in boreal summer, when surface wind and buoyancy forcing are strongest, the thermocline ridge is shallow (<90 m), and the mixed layer is deepening. These empirical results provide a framework for addressing intraseasonal and interannual climate variations, which are dynamically linked to the seasonal cycle, in the southwestern tropical Indian Ocean. They also provide a quantitative basis for assessing the accuracy of numerical ocean model simulations in the region.

scholarly journals A Test Study of an Energy and Mass Balance Model Application to a Site on Urumqi Glacier No. 1, Chinese Tian Shan

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2865
Author(s):  
Puyu Wang ◽  
Zhongqin Li ◽  
Christoph Schneider ◽  
Hongliang Li ◽  
Alexandra Hamm ◽  
...  
Keyword(s):  
Heat Flux ◽  
Mass Balance ◽  
Sensible Heat Flux ◽  
Shortwave Radiation ◽  
Balance Model ◽  
Mass Balance Model ◽  
Sensitivity Testing ◽  
Glacier Surface ◽  
Precipitation Decrease ◽  
Tian Shan

In this study, energy and mass balance is quantified using an energy balance model to represent the glacier melt of Urumqi Glacier No. 1, Chinese Tian Shan. Based on data from an Automatic Weather Station (4025 m a.s.l) and the mass balance field survey data nearby on the East Branch of the glacier, the “COupled Snowpack and Ice surface energy and Mass balance model” (COSIMA) was used to derive energy and mass balance simulations during the ablation season of 2018. Results show that the modeled cumulative mass balance (−0.67 ± 0.03 m w.e.) agrees well with the in-situ measurements (−0.64 ± 0.16 m w.e.) (r2 = 0.96) with the relative difference within 5% during the study period. The correlation coefficient between modeled and observed surface temperatures is 0.88 for daily means. The main source of melt energy at the glacier surface is net shortwave radiation (84%) and sensible heat flux (16%). The energy expenditures are from net longwave radiation (55%), heat flux for snow/ice melting (32%), latent heat flux of sublimation and evaporation (7%), and subsurface heat flux (6%). The sensitivity testing of mass balance shows that mass balance is more sensitive to temperature increase and precipitation decrease than temperature decrease and precipitation increase.

scholarly journals Analysis of a 3 year meteorological record from the ablation zone of Morteratschgletscher, Switzerland: energy and mass balance

2000 ◽  
Vol 46 (155) ◽  
pp. 571-579 ◽  
Author(s):  
J. Oerlemans
Keyword(s):  
Heat Flux ◽  
Sensible Heat Flux ◽  
Longwave Radiation ◽  
Solar Radiation Pressure ◽  
Turbulent Energy ◽  
Snow Accumulation ◽  
Shortwave Radiation ◽  
Glacier Surface ◽  
The Mean ◽  
Snow Temperature

AbstractSince 1 October 1995, an automatic weather station has been operated on the tongue of Morteratschgletscher, Switzerland. The station stands freely on the ice, and sinks with the melting glacier surface. It is located at 2100 m a.s.l., and measures air temperature, wind speed and direction, incoming and reflected solar radiation, pressure and snow temperature. A sonic ranger, mounted to stakes drilled into the ice, measures surface height from which melt rates and snow accumulation can be derived. In this paper the data for the period 1 October 1995 to 30 September 1998 are used to evaluate the surface energy balance. The turbulent energy fluxes are calculated with the bulk method. The turbulent exchange coefficient Ch is used as a control parameter. With Ch = 0.00127 the calculated melt equals the observed melt, which is 17.70 m w.e. over the 3 years. When averaged over the time when melting occurs (i.e. 35% of the time), the mean surface heat flux equals 191 W m−2. Net shortwave radiation contributes 177 W m−2, net longwave radiation −25 W m−2, the sensible-heat flux 31 W m−2 and the latent-heat flux 8 W m−2.

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