A study of low level jet characteristics using a sodar-RASS profiling system

2003 ◽  
Author(s):  
C.G. Helmis ◽  
Ch.H. Halios ◽  
D.N. Asimakopoulos
Keyword(s):  
Low Level ◽  
Low Level Jet ◽  
Jet Characteristics

scholarly journals Low-level jet characteristics over the Arctic Ocean in spring and summer

2013 ◽  
Vol 13 (1) ◽  
pp. 2125-2153
Author(s):  
L. Jakobson ◽  
T. Vihma ◽  
E. Jakobson ◽  
T. Palo ◽  
A. Männik ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Temperature Inversion ◽  
The Arctic ◽  
Jet Streams ◽  
Central Arctic Ocean ◽  
Turbulent Layer ◽  
Low Level ◽  
Low Level Jet ◽  
Jet Characteristics

Abstract. Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the bases of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46%) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationship between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated to transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations, gusts, and fronts were detected. In approximately 50% of the observed LLJs the generation mechanism remained unclear, but in most of these cases the wind speed was strong in the whole vertical profile, the jet core representing only a weak maximum. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.

scholarly journals Low-level jets over the North Sea based on ERA5 and observations: together they do better

2019 ◽  
Vol 4 (2) ◽  
pp. 193-209 ◽  
Author(s):  
Peter C. Kalverla ◽  
James B. Duncan Jr. ◽  
Gert-Jan Steeneveld ◽  
Albert A. M. Holtslag
Keyword(s):  
Wind Speed ◽  
North Sea ◽  
Measured Quantity ◽  
Valuable Insight ◽  
Low Level ◽  
Low Level Jets ◽  
Low Level Jet ◽  
Jet Characteristics ◽  
The Impact

Abstract. Ten years of ERA5 reanalysis data are combined with met-mast and lidar observations from 10 offshore platforms to investigate low-level jet characteristics over the Dutch North Sea. The objective of this study is to combine the best of two worlds: (1) ERA5 data with a large spatiotemporal extent but inherent accuracy limitations due to a relatively coarse grid and an incomplete representation of physical processes and (2) observations that provide more reliable estimates of the measured quantity but are limited in both space and time. We demonstrate the effect of time and range limitations on the reconstructed wind climate, with special attention paid to the impact on low-level jets. For both measurement and model data, the representation of wind speed is biased. The limited temporal extent of observations leads to a wind speed bias on the order of ±1 m s−1 as compared to the long-term mean. In part due to data-assimilation strategies that cause abrupt discontinuities in the diurnal cycle, ERA5 also exhibits a wind speed bias of approximately 0.5 m s−1. The representation of low-level jets in ERA5 is poor in terms of a one-to-one correspondence, and the jets appear vertically displaced (“smeared out”). However, climatological characteristics such as the shape of the seasonal cycle and the affinity with certain circulation patterns are represented quite well, albeit with different magnitudes. We therefore experiment with various methods to adjust the modelled low-level jet rate to the observations or, vice versa, to correct for the erratic nature of the short observation periods using long-term ERA5 information. While quantitative uncertainty is still quite large, the presented results provide valuable insight into North Sea low-level jet characteristics. These jets occur predominantly for circulation types with an easterly component, with a clear peak in spring, and are concentrated along the coasts at heights between 50 and 200 m. Further, it is demonstrated that these characteristics can be used as predictors to infer the observed low-level jet rate from ERA5 data with reasonable accuracy.

Summertime low-level jet characteristics measured by sodars over rural and urban areas

2009 ◽  
Vol 18 (3) ◽  
pp. 289-295 ◽  
Author(s):  
Margarita Kallistratova ◽  
Rostislav D. Kouznetsov ◽  
Dmitrii D. Kuznetsov ◽  
Irina N. Kuznetsova ◽  
Murat Nakhaev ◽  
...  
Keyword(s):  
Urban Areas ◽  
Low Level ◽  
Rural And Urban Areas ◽  
Rural And Urban ◽  
Low Level Jet ◽  
Jet Characteristics

Nocturnal Low-Level Jet Characteristics Over Kansas During Cases-99

2002 ◽  
Vol 105 (2) ◽  
pp. 221-252 ◽  
Author(s):  
R.M. Banta ◽  
R. K. Newsom ◽  
J. K. Lundquist ◽  
Y. L. Pichugina ◽  
R. L. Coulter ◽  
...  
Keyword(s):  
Low Level ◽  
Low Level Jet ◽  
Jet Characteristics

scholarly journals Low-level jets over the North Sea based on ERA5 and observations: together they do better

2019 ◽  
Author(s):  
Peter C. Kalverla ◽  
James B. Duncan Jr. ◽  
Gert-Jan Steeneveld ◽  
Albert A. M. Holtslag
Keyword(s):  
Wind Speed ◽  
North Sea ◽  
Measured Quantity ◽  
Valuable Insight ◽  
Offshore Platforms ◽  
Low Level ◽  
Low Level Jets ◽  
Low Level Jet ◽  
Jet Characteristics ◽  
The Impact

Abstract. Ten years of ERA5 reanalysis data are combined with met-mast and LiDAR observations from ten offshore platforms to investigate low-level jet characteristics over the Dutch North Sea. The objective of this study is to combine the best of two worlds: (1) ERA5 data with large spatiotemporal extent but inherent accuracy limitations due to a relatively coarse grid and an incomplete representation of physical processes, and (2) observations that provide more reliable estimates of the measured quantity, but are limited in both space and time. We demonstrate the effect of time and range limitations on the reconstructed wind climate, with special attention paid to the impact on low-level jets. For both measurement and model data, the representation of wind speed is biased. The limited temporal extent of observations leads to a wind speed bias on the order of 1 m s−1. In part due to data-assimilation strategies that cause abrupt discontinuities in the diurnal cycle, ERA5 also exhibits a wind speed bias of approximately 0.5 m s−1. Representation of low-level jets in ERA5 is poor in terms of a one-to-one correspondence, and the jets appear vertically displaced (`smeared out'). However, climatological characteristics such as the shape of the seasonal cycle and the affinity with certain circulation patterns are represented quite well, albeit with different magnitudes. We therefore experiment with various methods to adjust modelled low-level jet rate to the observations or, vice versa, to correct for the erratic nature of the short observation periods using long-term ERA5 information. While quantitative uncertainty is still quite large, the presented results provide valuable insight into North Sea low-level jet characteristics. These jets occur predominantly for circulation types with an easterly component, with a clear peak in spring, and concentrate along the coasts at heights between 50–200 m. Further, it is demonstrated that these characteristics can be used as predictors to infer the observed low-level jet rate from ERA5 data with reasonable accuracy.

scholarly journals Low-level jet characteristics over the Arctic Ocean in spring and summer

2013 ◽  
Vol 13 (21) ◽  
pp. 11089-11099 ◽  
Author(s):  
L. Jakobson ◽  
T. Vihma ◽  
E. Jakobson ◽  
T. Palo ◽  
A. Männik ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Temperature Inversion ◽  
The Arctic ◽  
Inertial Oscillations ◽  
Central Arctic Ocean ◽  
Turbulent Layer ◽  
Low Level ◽  
Low Level Jet ◽  
Jet Characteristics

Abstract. Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the basis of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46 ± 8%) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationships between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but when inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for the generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated with transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations and gusts were detected. As many as 49% of the LLJs observed were associated with a frontal passage, which provides favourable conditions for baroclinicity, inertial oscillations, and gusts. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.

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