Impact of low-level jets on the nocturnal urban heat island intensity in Oklahoma city

Xiao Ming Hu, Petra M. Klein, Ming Xue, Julie K. Lundquist, Fuqing Zhang, Youcun Qi

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

Previous analysis of Oklahoma City (OKC), Oklahoma, temperature data indicated that urban heat islands (UHIs) frequently formed at night and the observed UHI intensity was variable (1°-4°C). The current study focuses on identifying meteorological phenomena that contributed to the variability of nocturnal UHI intensity in OKC during July 2003. Two episodes, one with a strong UHI signature and one with a weak signature, were studied in detail using observations along with simulations with the Weather Research and Forecasting model. Mechanical mixing associated with low-level jets (LLJs) played a critical role in moderating the nocturnal UHI intensity. During nights with weak LLJs or in the absence of LLJs, vertical mixing weakened at night and strong temperature inversions developed in the rural surface layer as a result of radiative cooling. The shallow stable boundary layer (SBL < 200 m) observed under such conditions was strongly altered inside the city because rougher and warmer surface characteristics caused vertical mixing that eroded the near-surface inversion. Accordingly, temperatures measured within the urban canopy layer at night were consistently higher than at nearby rural sites of comparable height (by ∼3°-4°C). During nights with strong LLJs, however, the jets facilitated enhanced turbulent mixing in the nocturnal boundary layer. As a consequence, atmospheric stability was much weaker and urban effects played a much less prominent role in altering the SBL structure; therefore, UHI intensities were smaller (<1°C) during strong LLJs. The finding that rural inversion strength can serve as an indicator for UHI intensity highlights that the structure of the nocturnal boundary layer is important for UHI assessments.

Original languageEnglish (US)
Pages (from-to)1779-1802
Number of pages24
JournalJournal of Applied Meteorology and Climatology
Volume52
Issue number8
DOIs
StatePublished - 2013

Fingerprint

heat island
nocturnal boundary layer
vertical mixing
temperature inversion
city
turbulent mixing
surface layer
boundary layer
temperature
canopy
cooling
weather

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Hu, Xiao Ming ; Klein, Petra M. ; Xue, Ming ; Lundquist, Julie K. ; Zhang, Fuqing ; Qi, Youcun. / Impact of low-level jets on the nocturnal urban heat island intensity in Oklahoma city. In: Journal of Applied Meteorology and Climatology. 2013 ; Vol. 52, No. 8. pp. 1779-1802.
@article{d150e613336a45888db84084cfe12112,
title = "Impact of low-level jets on the nocturnal urban heat island intensity in Oklahoma city",
abstract = "Previous analysis of Oklahoma City (OKC), Oklahoma, temperature data indicated that urban heat islands (UHIs) frequently formed at night and the observed UHI intensity was variable (1°-4°C). The current study focuses on identifying meteorological phenomena that contributed to the variability of nocturnal UHI intensity in OKC during July 2003. Two episodes, one with a strong UHI signature and one with a weak signature, were studied in detail using observations along with simulations with the Weather Research and Forecasting model. Mechanical mixing associated with low-level jets (LLJs) played a critical role in moderating the nocturnal UHI intensity. During nights with weak LLJs or in the absence of LLJs, vertical mixing weakened at night and strong temperature inversions developed in the rural surface layer as a result of radiative cooling. The shallow stable boundary layer (SBL < 200 m) observed under such conditions was strongly altered inside the city because rougher and warmer surface characteristics caused vertical mixing that eroded the near-surface inversion. Accordingly, temperatures measured within the urban canopy layer at night were consistently higher than at nearby rural sites of comparable height (by ∼3°-4°C). During nights with strong LLJs, however, the jets facilitated enhanced turbulent mixing in the nocturnal boundary layer. As a consequence, atmospheric stability was much weaker and urban effects played a much less prominent role in altering the SBL structure; therefore, UHI intensities were smaller (<1°C) during strong LLJs. The finding that rural inversion strength can serve as an indicator for UHI intensity highlights that the structure of the nocturnal boundary layer is important for UHI assessments.",
author = "Hu, {Xiao Ming} and Klein, {Petra M.} and Ming Xue and Lundquist, {Julie K.} and Fuqing Zhang and Youcun Qi",
year = "2013",
doi = "10.1175/JAMC-D-12-0256.1",
language = "English (US)",
volume = "52",
pages = "1779--1802",
journal = "Journal of Applied Meteorology and Climatology",
issn = "1558-8424",
publisher = "American Meteorological Society",
number = "8",

}

Impact of low-level jets on the nocturnal urban heat island intensity in Oklahoma city. / Hu, Xiao Ming; Klein, Petra M.; Xue, Ming; Lundquist, Julie K.; Zhang, Fuqing; Qi, Youcun.

In: Journal of Applied Meteorology and Climatology, Vol. 52, No. 8, 2013, p. 1779-1802.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Impact of low-level jets on the nocturnal urban heat island intensity in Oklahoma city

AU - Hu, Xiao Ming

AU - Klein, Petra M.

AU - Xue, Ming

AU - Lundquist, Julie K.

AU - Zhang, Fuqing

AU - Qi, Youcun

PY - 2013

Y1 - 2013

N2 - Previous analysis of Oklahoma City (OKC), Oklahoma, temperature data indicated that urban heat islands (UHIs) frequently formed at night and the observed UHI intensity was variable (1°-4°C). The current study focuses on identifying meteorological phenomena that contributed to the variability of nocturnal UHI intensity in OKC during July 2003. Two episodes, one with a strong UHI signature and one with a weak signature, were studied in detail using observations along with simulations with the Weather Research and Forecasting model. Mechanical mixing associated with low-level jets (LLJs) played a critical role in moderating the nocturnal UHI intensity. During nights with weak LLJs or in the absence of LLJs, vertical mixing weakened at night and strong temperature inversions developed in the rural surface layer as a result of radiative cooling. The shallow stable boundary layer (SBL < 200 m) observed under such conditions was strongly altered inside the city because rougher and warmer surface characteristics caused vertical mixing that eroded the near-surface inversion. Accordingly, temperatures measured within the urban canopy layer at night were consistently higher than at nearby rural sites of comparable height (by ∼3°-4°C). During nights with strong LLJs, however, the jets facilitated enhanced turbulent mixing in the nocturnal boundary layer. As a consequence, atmospheric stability was much weaker and urban effects played a much less prominent role in altering the SBL structure; therefore, UHI intensities were smaller (<1°C) during strong LLJs. The finding that rural inversion strength can serve as an indicator for UHI intensity highlights that the structure of the nocturnal boundary layer is important for UHI assessments.

AB - Previous analysis of Oklahoma City (OKC), Oklahoma, temperature data indicated that urban heat islands (UHIs) frequently formed at night and the observed UHI intensity was variable (1°-4°C). The current study focuses on identifying meteorological phenomena that contributed to the variability of nocturnal UHI intensity in OKC during July 2003. Two episodes, one with a strong UHI signature and one with a weak signature, were studied in detail using observations along with simulations with the Weather Research and Forecasting model. Mechanical mixing associated with low-level jets (LLJs) played a critical role in moderating the nocturnal UHI intensity. During nights with weak LLJs or in the absence of LLJs, vertical mixing weakened at night and strong temperature inversions developed in the rural surface layer as a result of radiative cooling. The shallow stable boundary layer (SBL < 200 m) observed under such conditions was strongly altered inside the city because rougher and warmer surface characteristics caused vertical mixing that eroded the near-surface inversion. Accordingly, temperatures measured within the urban canopy layer at night were consistently higher than at nearby rural sites of comparable height (by ∼3°-4°C). During nights with strong LLJs, however, the jets facilitated enhanced turbulent mixing in the nocturnal boundary layer. As a consequence, atmospheric stability was much weaker and urban effects played a much less prominent role in altering the SBL structure; therefore, UHI intensities were smaller (<1°C) during strong LLJs. The finding that rural inversion strength can serve as an indicator for UHI intensity highlights that the structure of the nocturnal boundary layer is important for UHI assessments.

UR - http://www.scopus.com/inward/record.url?scp=84884361073&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84884361073&partnerID=8YFLogxK

U2 - 10.1175/JAMC-D-12-0256.1

DO - 10.1175/JAMC-D-12-0256.1

M3 - Article

AN - SCOPUS:84884361073

VL - 52

SP - 1779

EP - 1802

JO - Journal of Applied Meteorology and Climatology

JF - Journal of Applied Meteorology and Climatology

SN - 1558-8424

IS - 8

ER -