Simulation of Climatology and Interannual Variability of the North African Monsoon: An Analysis Based on FGOALS-g3 Model
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摘要: 本文基于参加第六次“国际耦合模式比较计划”(CMIP6)的IAP/LASG气候系统模式FGOALS-g3的耦合(Historical)与非耦合(AMIP)试验结果,通过与观测和再分析资料的比较,评估了FGOALS-g3模式Historical与AMIP试验对北非地区1979~2010年7~9月降水气候态和年际变率的模拟能力;利用水汽收支方程与回归分析研究了模式模拟降水偏差的原因;通过比较耦合与非耦合试验的模拟结果,分析了海气耦合过程对非洲季风模拟偏差的影响。结果表明,在气候平均态上,Historical与AMIP试验模拟的降水均较观测偏少且位置偏南,模拟的北非夏季西南季风环流偏弱。AMIP试验模拟的萨赫勒和北非季风区降水与观测降水的空间相关系数分别为0.80、0.62,而Historical试验仅有0.74和0.46,且AMIP试验对应的均方根误差为2.58、3.23 mm,Historical试验为3.30 mm、4.01 mm,说明与Historical试验相比,AMIP试验的模拟偏差更小。水汽收支分析表明,Historical与AMIP试验均低估了北非季风区水汽辐合,同时低估了垂直水汽平流项与蒸发项,高估了水平水汽平流项,导致模式模拟的降水偏少,且Historical试验的偏差大于AMIP试验。在年际变率方面,观测中,北非夏季风降水—ENSO呈负相关关系。AMIP试验能够模拟出ENSO正位相时北非夏季降水的负异常,且较观测的负异常偏强,而Historical试验模拟的负相关关系并不显著。AMIP试验高估了北非地区垂直运动、热带东风急流与低层季风环流对ENSO的响应强度,导致降水异常偏强,而Historical试验低估了上述响应强度,产生弱降水负异常。水汽收支表明,北非夏季降水—ENSO的负相关关系由垂直水汽平流项的动力项主导。AMIP试验高估了垂直平流项及其动力项的贡献,但Historical试验高估水平平流项与垂直热力项异常的贡献,说明Historical试验模拟的北非夏季降水—ENSO相关关系偏差与水平平流项异常的抑制作用有关。
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关键词:
- 北非夏季风 /
- FGOALS-g3模式 /
- 模式评估 /
- 气候态 /
- 年际变率
Abstract: Based on the comparison with observation and reanalysis data, the study evaluated the performance of the Atmospheric Model Intercomparison Project (AMIP) and the Coupled Model Intercomparison Project historical experiments (Historical) of the IAP/LASG climate system model FGOALS-g3 in simulating climatology and interannual variability of July–August–September seasonal-mean North Africa summer monsoon (NASM) and Sahel precipitation, explained the bias by moisture budget and regression analysis, and investigated the influence of ocean-atmosphere coupling by comparing AMIP and Historical. The results showed that both Historical and AMIP experiments underestimated precipitation, with weaker southwest monsoon winds and further southern rainfall positions. The pattern correlation coefficients of precipitation in the Sahel and North Africa monsoon regions simulated by AMIP are 0.80 and 0.62, respectively, which are 0.74 and 0.46 simulated by Historical, and the corresponding root mean square errors are 2.58 and 3.23 mm, which are 3.30 and 4.01 mm in the Historical experiment, indicating that the deviation of AMIP is smaller than that of Historical. Historical and AMIP both underestimated water vapor convergence over the NASM region, estimating less vertical moisture advection and evaporation and more horizontal moisture advection than observed, resulting in dry biases. In terms of interannual variability, the observation shows that summer monsoon rainfall in North Africa is negatively correlated with ENSO. AMIP can reproduce the ENSO–NASM negative relationship better than observation. However, Historical cannot reasonably simulate the relationship on the interannual time scale. AMIP overestimates ENSO circulation responses, including descending anomalies, weaker tropical easterly jets, and decreased low-level monsoons over North Africa, all of which contribute to the stronger precipitation negative anomaly. In contrast, Historical underestimates the above ENSO-related response, resulting in feeble precipitation negative anomaly. Vertical moisture advection anomalies, particularly the dynamic element of vertical moisture advection anomalies, dominate the ENSO–NASM negative relationship, according to moisture budget research. AMIP agrees with observation, but it overestimates the above term, resulting in more negative rainfall anomalies, while Historical overestimates horizontal advection and vertical thermodynamic anomalies, which indicates that horizontal advection anomalies cause the inhibited simulation of the ENSO–NASM negative relationship.-
Key words:
- North Africa summer monsoon /
- FGOALS-g3 model /
- Model evaluation /
- Climatology /
- Interannual variability
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图 2 1979~2010年(a)GPCP(Global Precipitation Climatology Project)观测资料和(b–d)FGOALS-g3模式模拟结果中18°W~40°E纬向平均的降水量(填色,单位:mm d−1)的年循环:(b)AMIP试验;(c)Hostorical试验;(d)Hostorical试验减去AMIP试验结果。1979~2010年(e)萨赫勒地区和(f)北非季风区区域平均降水量的年循环。(b、c)中右上方数字分别是AMIP、Historical试验与GPCP观测资料在7~9月(JAS)0°~20°N(图中虚线框)范围内相关系数
Figure 2. Annual cycle climatology for precipitation (shaded color, units: mm d−1) averaged between 18°W and 40°E during 1979–2010 from (a) GPCP (Global Precipitation Climatology Project) dataset and (b–d) simulations of FGOALS-g3: (b) AMIP simulations, (c) Historical simulations, (d) Historical simulations minus AMIP simulations. Annual cycle of area mean precipitation of (e) the Sahel and (f) NASM regions during 1970–2010. The numbers in the upper-right corner of (b, c) are the correlations between AMIP and Historical simulations with GPCP precipitation over 0°–20°
$ ° $ N in July–September (JAS, the dashed region), respectively图 3 1979~2010年观测与FGOALS-g3模式模拟的7~9月季节平均北非季风区(粗黑框)与萨赫勒地区(红框)的气候态降水量(阴影,单位:mm d−1)与925 hPa风场(矢量,单位:m s−1)及其偏差分布:(a)GPCP降水和ERA_Interim环流资料;(b)Historical减去AMIP试验结果;(c)AMIP试验;(d)AMIP试验结果减去观测结果(obs);(e)Historical试验;(f)Historical试验结果减去观测结果(obs)。(c, e)中右上方数字分别是AMIP与Historical试验模拟的萨赫勒与北非季风区JAS季节平均降水与GPCP降水之间的空间相关系数
Figure 3. Spatial distributions of July–August–September (JAS) seasonal-mean precipitation (shaded color, units: mm d−1) and 925 hPa winds (vectors, units: m s−1) in the North Africa Summer Monsoon (NASM, the black bold line region) and Sahel (the red line region) regions during 1979–2010: (a) GPCP&ERA_Interim; (b) Historical simulation minus AMIP simulation; (c) AMIP simulation; (d) AMIP simulation minus observation; (e) Historicalsimulation; (f) Historical simulation minus observation. The numbers in the upper-right corner in (c, e) are the pattern correlations of precipitation between AMIP and Historical with GPCP in the Sahel and NASM, respectively
图 4 1979~2010年观测和模拟的7~9月平均的北非地区海平面气压(等值线,单位:hPa)与2 m气温(填色,单位:°C)分布:(a)ERA_Interim资料;(b)AMIP试验;(c)Historical试验;(d)Historical减去AMIP试验结果
Figure 4. Spatial distributions of JAS seasonal-mean North Africa sea level pressure (contours, units: hPa) and 2-m temperature (shaded color, units: °C) during 1979–2010 from (a) ERA_Interim data, (b) AMIP simulations, (c) Historical simulations, and (d) Historical simulations minus AMIP simulations
图 5 1979~2010年观测和模拟的18°W~40°E纬向平均的7~9月平均纬向风的纬度—高度垂直剖面(填色,单位:m s−1)与经圈环流及其偏差(矢量,经向风单位:m s−1,垂直速度单位:100 Pa s−1):(a)ERA_Interim资料;(b)AMIP试验;(c)Historical试验;(d)Historical减去AMIP试验结果
Figure 5. Spatial distributions of JAS seasonal-mean zonal winds (shaded color, units: m s−1) and meridional circulation (vectors, units of meridional winds: m s−1, units of vertical velocity: 100 Pa s−1) zonally averaged over 18°W–40°E during 1979–2010: (a) ERA_Interim data; (b) AMIP simulations; (c) Historical simulations; (d) Historical simulations minus AMIP simulations
图 6 1979~2010年7~9月平均的北非整层积分的水汽通量(矢量,单位:kg m−1 s−1)及其辐合(阴影,单位:10−5 kg m−2 s−1)的空间分布:(a)ERA_Interim资料;(b)Historical减去AMIP试验结果;(c)AMIP试验;(d)AMIP试验相对ERA_Interim资料的偏差;(e)Historical试验;(f)Historical试验相对ERA_Interim资料的偏差
Figure 6. Spatial distributions of JAS seasonal-mean water vapor transport fluxes (contour, units: kg m−1 s−1) and their divergence (shaded color, units: 10−5 kg m−2 s−1) during 1979–2010: (a) ERA_Interim data; (b) Historical simulations minus AMIP simulations; (c) AMIP simulations, (d) AMIP simulations minus ERA_Interim data; (e) Historical simulations; (f) Historical simulations minus ERA_Interim data
图 7 (a–o)1979~2010年ERA_Interim资料(左列)、Historical试验(中间列)和AMIP试验(右列)7~9月季节平均北非水汽收支分解项[公式(2),单位:mm d−1]的空间分布:(a–c)降水量项(P);(d–f)蒸发量项(E);(g–i)水汽的垂直平流项(
$-\langle{\omega {\partial }_{p}q}\rangle$ );(j–l)水汽的水平平流项($-\left\langle{{\boldsymbol{V}}_{h}\cdot {\nabla }_{\mathrm{h}}q}\right\rangle$ );(m–o)残差项(res)。1979~2010年7~9月季节平均的(p)萨赫勒与(q)北非季风区区域平均的水汽收支各项[公式(2)]柱状图Figure 7. (a–o) Spatial distributions of JAS seasonal-mean water vapor budget components (equation 2) over North Africa (units: mm d−1
$ \mathrm{m}\mathrm{m}{\mathrm{d}}^{-1} $ ) during 1979–2010 from ERA_Interim data (left column), Historical simulations (middle column), and AMIP simulations (right column): (a–c) Precipitation term (P); (d–f) evaporation term (E); (g–i) vertical moisture advection term ($-\langle{\omega {\partial }_{p}q}\rangle$ ); (j–l) horizontal moisture advection term ($-\left\langle{{\boldsymbol{V}}_{h}\cdot {\nabla }_{\mathrm{h}}q}\right\rangle$ ); (m–o) residual term (res). (p, q) Histogram of JAS seasonal-mean water vapor budget components (equation 2) averaged over the (p) Sahel and (q) NASM (North Africa summer monsoon) regions during 1979–2010图 8 1979~2010年观测和模拟的北非7~9月降水量年际变率的空间分布(单位:mm d−1,通过10年高通滤波与去趋势处理):(a)GPCP资料;(b)Historical减去AMIP试验结果;(c)AMIP试验;(d)AMIP试验结果相对于GPCP资料的偏差;(e)Historical试验;(f)Historical试验结果相对于GPCP资料的偏差。其中Historical试验为6个成员的年际变率的集合平均,AMIP试验为5个成员年际变率的集合平均。(c、e)中r分别表示萨赫勒地区(红框)与北非季风区(黑框)模式结果与观测的空间相关系数
Figure 8. Standard deviations of the interannual variability of JAS seasonal-mean precipitation after 10-year high pass filtering and detrending over North Africa (units: mm d−1) during 1979–2010: (a) GPCP datasets; (b) Historical simulations minus AMIP simulations; (c) AMIP simulations; (d) AMIP simulations minus GPCP datasets ; (e) Historical simulations; (f) Historical simulations minus GPCP datasets. The interannual variability of Historical and AMIP simulations are the results of the multi-member mean of six and five members, respectively. The numbers in the upper-right corner of (c, e) are the pattern correlations of precipitation between AMIP and Historical with GPCP in the Sahel (the red box) and NASM (the black box) regions, respectively
图 9 1979~2010年观测和模拟的标准化7~9月平均Niño3.4指数回归的降水量异常(填色,单位:mm d−1)与850 hPa环流异常(矢量,单位:m s−1)的空间分布(通过10年高通滤波与去趋势处理):(a)GPCP降水和ERA_Interim环流场资料(obs);(b)Historical减去AMIP试验结果;(c)AMIP试验;(d)AMIP相对于观测的偏差;(e)Historical试验;(f)Historical相对于观测的偏差。其中Historical试验为6个成员回归的集合平均,AMIP试验为5个成员回归的集合平均。(c、e)右上角的r分别表示萨赫勒地区(红框)与北非季风区(黑框)模式结果与观测的空间相关系数,(a)中打点区域表示回归系数通过95%的显著性检验,(c)中打点区域表示至少80%AMIP成员的回归系数通过95%的显著性检验,(e)中打点区域表示Historical试验的回归系数通过80%成员的同号检验
Figure 9. Spatial distributions of JAS seasonal-mean precipitation anomalies (shaded color, units: mm d−1) and 850 hPa winds anomalies (vectors, units: m s−1) regressed onto standardized JAS Niño3.4 index (after 10-year high pass filtering and detrending) over North Africa during 1979–2010: (a) GPCP precipitation and ERA_Interim winds datasets (obs); (b) Historical simulations minus AMIP simulations; (c) AMIP simulations; (d) AMIP simulations minus obs;(e) Historical simulations; (f) Historical simulations minus obs. The regression coefficients of Historical and AMIP are the results of the multi-member mean of six and five members, respectively. The numbers in the upper-right corner of (c, e) are the pattern correlations of precipitation between AMIP and Historical simulations with GPCP in the Sahel and NASM regions, respectively. The dotted areas of (a) pass the test at a confidence level of 95%. (c) is from AMIP, with five members, in which the dot areas represent at least 80% of members passing the test at a 95% confidence level. (e) is from Historical with six members, in which the dotted areas pass the test of the same sign at a level of 80%
图 10 1979~2010年观测和模拟的标准化7~9月平均Niño3.4指数(通过10年高通滤波与去趋势处理)回归的18°W~40°E平均纬向风的纬度—高度垂直剖面(填色,单位:m s−1)与经圈环流及其偏差(矢量,经向风单位:m s−1,垂直速度单位:100 Pa s−1)的空间分布:(a)ERA_Interim资料;(b)AMIP试验;(c)Historical试验;(d)Historical相对AMIP试验结果的偏差。其中Historical试验为6个成员回归的集合平均,AMIP试验为5个成员回归的集合平均。(a)中打点区域表示回归系数通过95%的显著性检验,(b)中打点区域表示至少80% AMIP成员的回归系数通过95%的显著性检验,(c)中打点区域表示Historical试验的回归系数通过80%成员的同号检验
Figure 10. Spatial distributions of JAS seasonal-mean zonal winds anomalies (shaded color, units: m s−1) and meridional circulation anomalies (vectors, units of meridional winds: m s−1, units of vertical velocity: 100 Pa s−1) zonally averaged over 18°W–40°E regressed onto the standardized JAS Niño3.4 index (after 10-year high pass filtering and detrending) during 1979–2010: (a) ERA_Interim data; (b) AMIP simulations; (c) Historical simulations; (d) Historical simulations minus AMIP simulations. The regression coefficient of Historical and AMIP simulations is the results of the multi-member mean of six and five members, respectively. The dotted areas of (a) pass the test at a 95% confidence level. (b) is from AMIP with five members, in which the dotted areas represent at least 80% of members passing the test at a 95% confidence level. (c) is from Historical with six members, in which the dotted areas pass the test of the same sign at a level of 80%
图 11 1979~2010年HadISST海温、ERA_Interim资料(左列)以及AMIP试验(中间列)和Historical试验(右列)模拟的标准化7~9月Niño3.4指数回归的物理量异常(均通过10年高通滤波与去趋势处理)的空间分布:(a1–a3)海表温度异常(填色,单位:K);(b1–b3)200 hPa速度势异常(填色,单位:106 m2 s−1)和辐散风异常(矢量,单位:m s−1);(c1–c3)200 hPa纬向风异常(填色,单位:m s−1);(d1–d3)850 hPa 位势高度异常(填色,单位:gpm);(e1–e3)925 hPa 流函数异常(填色,单位:106 m2 s−1)。左列图中打点区域表示回归系数通过95%的显著性检验,中间列打点区域表示至少80% AMIP成员的回归系数通过95%的显著性检验,右列图中打点区域表示Historical试验的回归系数通过80%成员的同号检验
Figure 11. Spatial distributions of JAS seasonal-mean (a1–a3) sea surface temperature anomalies (shaded color, units: K), (b1–b3) 200 hPa velocity potential anomalies (shaded color, units: 106 m2 s−1) and divergent wind anomalies (vectors, units: m s−1), (c1–c3) 200 hPa zonal wind anomalies (shaded color, units: m s−1), (d1–d3) 850 hPa geopotential height anomalies (color shaded; units: gpm), and (e1–e3) 925 hPa stream function anomalies (shaded color, units: 106 m2 s−1) regressed onto the standardized JAS Niño3.4 index(after 10-year high pass filtering and detrending) of HadISST SST and ERA_Interim data (left column), AMIP simulation (middle column) and Historical simulation (right column). The dotted areas in left column represent the regressions pass the test at a confidence level of 95%The dotted areas in middle column represent at least 80% of members in AMIP simulations passing the test at a confidence level of 95%The dotted areas in right column represent regression passing the test of the same sign at a level of 80% for Historical simulations
图 12 (a–o)1979~2010年ERA_Interim资料(左列)、Historical试验(中间列)和AMIP试验(右列)中北非地区7~9月El Niño发展年水汽收支各项异常(公式3和4)的空间分布(填色,单位:mm d−1
$ \mathrm{m}\mathrm{m}{\mathrm{d}}^{-1} $ ):(a–c)降水异常(P′);(d–f)垂直水汽平流项异常($-{\langle{\omega {\partial }_{p}q}\rangle}'$ );(g–i)水平水汽平流项异常($-{\left\langle{{\boldsymbol{V}}_{h}\cdot {\nabla }_{\mathrm{h}}q}\right\rangle}'$ );(j–l)直水汽平流动力项异常($-\langle{{\omega }'{\partial }_{p}\overline{q}}\rangle$ );(m–o)垂直水汽平流热力项异常($-\langle{\overline{\omega }{\partial }_{p}{q}'}\rangle$ )。1979~2010年7~9月季节平均的(p)萨赫勒与(q)北非季风区区域平均的水汽收支异常项(公式3和4)柱状图Figure 12. (a–o) Spatial distributions of JAS seasonal-mean water vapor budget component anomalies (equations 3 and 4) in El Niño developing years over North Africa (units: mm d−1
$ \mathrm{m}\mathrm{m}{\mathrm{d}}^{-1} $ ) from ERA_Interim data (left column), Historical simulations (middle column), and AMIP simulations (right column) during 19792010: (a–c) Precipitation anomalies; (d–f) vertical moisture advection anomalies ($-{\langle{\omega {\partial }_{p}q}\rangle}'$ ) ; (g–i) horizontal moisture advection anomalies ($-{\left\langle{{\boldsymbol{V}}_{h}\cdot {\nabla }_{\mathrm{h}}q}\right\rangle}'$ ); (j–l) dynamic term of vertical moisture advection anomalies ($-\langle{{\omega }'{\partial }_{p}\overline{q}}\rangle$ ) ; (m-o) thermodynamic term of vertical moisture advection anomalies ($-\langle{\overline{\omega }{\partial }_{p}{q}{{'}}}\rangle$ ). Histogram of JAS seasonal-mean water vapor budget components anomalies (equations 3 and 4) averaged over the (p) Sahel and (q) NASM regions during 1979–2010 -
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